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LIBRARY
Michigan State
University

 

 

 

This is to certify that the

dissertation entitled

Growth Responses of Corn (Zea mays L.)

to Intermittent Soil Water Deficits

presented by

Dennis Scott NeSmith

has been accepted towards fulfillment
of the requirements for

PhD. degree in Crop and Soil Science

 

 

QM]. EM;

 

 

y Major professor

Date March 19, 1990

 

MSU is an Affirmative Action/Equal Opportunity Institution 0-12771

PLACE N RETURN BOX to remove this checkout from your record.
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[—7

MSU Is An Affirmative Action/Equal Opportunity Inditution

GROWTH RESPONSES OF CORN (ZEA MAYS L.) TO
INTERMITTENT SOIL WATER DEFICITS

 

BY

Dennis Scott NeSmith

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Crop and Soil Sciences

1990

Q9C355¢AC{\<:

ABSTRACT

GROWTH RESPONSES OF CORN (ZEA MAYS L.) TO
INTERMITTENT SOIL WATER DEFICITS

BY

Dennis Scott NeSmith

An increased understanding of corn responses to
intermittent water deficits is a pmerequisite to achieving
goals of maintaining production and protecting the environment
in humid regions where supplemental irrigation is used. A.
rain shelter was employed to impose periodic drought on corn
at various growth stages in a field environment in Michigan,
and whole plant responses were examined. Results indicated
yield losses due to 18 to 21 day water deficits on a sandy
soil were 15 % to 25 % when the water shortage occurred during
pre-anthesis growth, were as great as 90 % when the deficit
occurred during anthesis, and were 25 95 to 40 % when the
deficit occurred during the grain filling period. A notable
correlation between water absorption from the upper 0.25 m of
soil and plant extension growth was observed. Reduction in
extension growth resulted in reduced size of leaves,
internodes, and ears that were expanding during the deficit
period, and the smallness was primarily attributable to
decreased. growth rate rather than shortened duration of
growth. Above ground biomass accumulation was less under
deficit conditions at all growth stages and was largely

attributable to reduced production of leaf area or increased

loss of green leaf area due to early senescence. Limited data
indicated leaf rolling, alteration in light interception, and
increased root growth at deeper soil depths also contributed
to the decline in above ground crop growth rate. Tasseling,
silking, and.beginning grain.fill were.delayed.by pre-anthesis
water deficits. Water shortages during anthesis caused as
much as 80 95 barren plants. The period of time from just
before anthesis until beginning linear grain filling was
determined to be critical.in obtaining substantial kernel set.
Maximizing grain number' per ‘unit area was important in
maintaining favorable yields, as little compensation in grain
weight was observed for plants with lower numbers of kernels.
Water deficits during grain filling reduced the duration of
linear filling more than the rate. Grain size distributions
demonstrated deficit plants had a larger percentage of grains

weighing less than 100 mg seed.1 than did irrigated plants.

ACKNOWLEDGEMENTS

I would like to extend a sincere appreciation to the many
people that have been involved in the various processes
leading up to this event in my life. First, there is my
advisor Dr. Joe T. Ritchie. He has allowed me opportunities
for personal and professional growth I feel I could have
obtained few places. He has often remained at arms length,
but that was so that I could learn the needed independence it
will take to set off on a scientific career of my own.
However; he has always been willing to take the time to listen
to my ideas as well as my gripes and grievances. -I am certain
that having him as a mentor will enhance my scientific
endeavors for many years to come. Thanks Dr. Ritchie.

In addition to my advisor, I would like to thank the
members of my graduate committee. These are Dr. Jim Flore,
Dr. Bernie Knezek, and Dr. Al Smucker. I feel that each of
these have added to my professional training in their own way.
I found the diversity intellectually stimulating and
rewarding.

I would like to thank those that assisted.me technically,

and that supported my projects financially over the past four

iv

years. First, I would like to recognize the help of the many
people at the Kellogg Biological Station that added to my
program. These are indeed too numerous to name, but I would
especially like to mention Mr. Jim Bronson as one of the
people that stands out clearly. I also appreciate the
support received through the MECP organization. I have
enjoyed being part of this program and group. Additionally,
I would like to acknowledge the financial support of Pioneer
Hi-Bred International, Inc. I would especially like to thank
their representative Dr. Bob Palmer who has given me
professional encouragement in addition to the Pioneer funds.

I need to extend gratitude to the many colleagues of the
Homer Nowlin Chair. Working with this group has been a great
joy and scientifically inspiring. The diversity of the group
has lent an education in itself. These are of course too
numerous to name, but.I‘want.to mention.Abelardo Nunez-Barrios
in particular. He made the work at KBS during the summers
much more enjoyable, especially the long rides down. Also, I
appreciate the hard work that Sharlene Rhines has put in for
me and the entire group. She certainly should not be over
looked.

I would like to thank my family including my parents,
brothers, and in-laws for their prayers and encouragement
through these past few years. Their support has made this
experience pleasant. I especially appreciate the values that

my parents taught me which have helped me to meet the many

challenges through the past few years. I appreciate their
leading me to Christ at an early age most of all. The
relationship with Him has been my source of strength, love,
and wisdom, all of which I needed to complete this task, or
any other which I may encounter. He is my Rock.

I would like to offer thanks in the only way I know how,
which is not nearly enough, to the most special person through
all of this endeavor. Suzanne, I love you. Once again you
have ventured along with me offering support beyond measure,
as well as comfort and companionship. There is no doubt in my
mind that without you in all of this, it would have little
meaning. II especially thank you for the birth of our son
Matthew Scott. He certainly helped to break the monotony of

it all, and he helps me keep everything in perspective.

vi

TABLE OF CONTENTS

List of Tables ......... ..... ........ . ........ .. ....... ...ix
List of Figures. ............. . ............. ....... ........ x
Introduction............. ................. . ............... 1
List of References ....... ......... ................... 7
Chapter 1. Pre-anthesis soil water deficit effect on

Chapter 2.

Chapter 3.

Chapter 4.

corn (Zea mays L.). I. Vegetative growth

and development......................... ...... 9
Abstract..................... ........ . ..... 9
Introduction....................... ...... .10
Materials and Methods.......... .......... .12
Results and Discussion.......... .......... 21
List of References.................. ...... 53

Pre-anthesis soil water deficit effect on
corn (Zea mays L.). II. Reproductive growth

and development....................... ...... .56
Abstract................... ............... 56
Introduction.................. .......... ..57
Materials and Methods......... ......... ...59
Results and Discussion ........... . ........ 61
List of References................. ....... 86

Pre-anthesis soil water deficit effect on
corn (Zea mays L.). III. Biomass and

nitrogen accumulation and partitioning ....... 88
Abstract...................... ........... .88
Introduction.............. ............. ...89
Materials and Methods.. ................. ..91
Results and Discussion....................94
List of References .......... . ........... .121

Effects of soil water deficits during
anthesis on field grown corn (Zea mays L.)..125

Abstract.......... ...... ............ ..... 125
Introduction............... ........ . ..... 126
Materials and Methods........... ..... ....127
Results and Discussion ................... 133
. List of References.. ..................... 146

vii

Chapter 5.

Corn (Zea mays L.) response to an

intermittent soil water deficit during

grain fillingOOOOOOOOOOO ..... 0.0.00.00000000148
Abstract... ..... . ............... . ........ 148
Introduction....... ........ ........ ...... 149
Materials and Methods ........... . ........ 153
Results and Discussion...................160
List of References ..................... ..200
Summary and Conclusions........... ............. . ........ 203
Appendix 1. Weather data for the 1987 growing season
at the Kellogg Biological Station .......... 207
Appendix 2. Weather data for the 1988 growing season
at the Kellogg Biological Station .......... 211
Appendix 3. Weather data for the 1989 growing season
at the Kellogg Biological Station .......... 215
Appendix 4. Relationship between above ground biomass
and height to the top leaf ligule from data
taken during 1989 .......................... 220
Appendix 5. Relationship between stem biomass and
height to the top leaf ligule from data
taken during l989............. ...... .. ..... 221
Appendix 6. Relationship between leaf biomass and
plant leaf area from data taken during
1989.... ................................... 222

viii

LIST OF TABLES

Table 4.1. Silking date, yield, grain number, grain
weight, and percent barren plants for treatments during

19870.......OOOOOOOOOOOOOOO...COOOOOOOOOOOOOO00.0.000000134

Table 4.2. Grain yield, grain number, grain weight,
percent barren plants, and harvest index for treatments
during 1988.............................................143

Table 5.1. Day of year (DOY) and thermal time after

planting (°Cd) when 50 % and 75 % Silking occurred for
treatments.................................. ..... .......161

Table 5.2. Nitrogen content of whole plants excluding
roots on July 31 (DOY 212) and of grain only on August

15 (DOY 227), September 6 (DOY 249), and September 27

(DOY 270)...............................................180

ix

LIST OF FIGURES

Figure 1.1. Soil water content of a Spinks soil at
different depths after saturation followed by three days
drainage and after more than forty days of drying by a
corn crop ..... ................ ................. . ......... 13

Figure 1.2. Thermal time accumulation during 1988 and
1989. There were two planting dates (P1 and P2) during
1989. Units were calculated using 8 °C as base

temperature .............................................. 16

Figure 1.3a. Irrigation amounts applied to treatments
during 1988. The region between vertical dashed lines
represents the period when no water was applied to pre-
anthesis deficit treatments .............................. 18

Figure 1.3b. Irrigation amounts applied to treatments
during 1989. The region between vertical dashed lines
represents the period when no water was applied to pre-
anthesis deficit treatments....... ...... . ....... ... ...... 19

Figure 1.4a. Soil water content of the 1.5 m profile
during 1988. Values are equivalent depth water. The
horizontal dashed line represents the estimated drained
upper limit of soil water, and the region between the
vertical dashed lines depicts the deficit period.........22

Figure 1.4b. Soil water content of the 1.5 m profile
during 1989. Values are equivalent depth water. The
horizontal dashed line represents the estimated drained
upper limit of soil water, and the region between the
vertical dashed lines depicts the deficit period ......... 23

Figure 1.5a. Relative extension growth of pre-anthesis
deficit plants during 1988 for hybrids 3540 and 3475 as
determined from leaves and from the height to the top

leaf ligule.... ..... .. ...... . ..... . ...................... 24

Figure 1.5b. Relative extension growth of pre-anthesis
deficit plants of the first planting date during 1989

for hybrids 3540 and 3475 as determined from leaves and
from the height to the top leaf ligule ................... 25

X

Figure 1.5c. Relative extension growth of pre-anthesis
deficit plants of the second planting date during 1989

for hybrids 3540 and 3475 as determined from leaves and
from the height to the top leaf ligule...................26

Figure 1.6a. Water absorption rates at depths of 0.00

to 0.25 m, 0.25 to 0.50 m, and 0.50 to 0.75 m during the
deficit period for the pre-anthesis deficit, first
planting date treatment during 1989 .......... .. .......... 28

Figure 1.6b. Water absorption rates at depths of 0.75

to 1.00 m, 1.00 to 1.25 m, and 1.25 to 1.50 m during the
deficit period for the pre-anthesis deficit, first
planting date treatment during 1989... .......... ... ...... 29

Figure 1.7a. Water absorption rates at depths of 0.00

to 0.25 m, 0.25 to 0.50 m, and 0.50 to 0.75 m during the
deficit period for the pre-anthesis deficit, second
planting date treatment during 1989.... ....... . .......... 30

Figure 1.7b. Water absorption rates at depths of 0.75

to 1.00 m, 1.00 to 1.25 m, and 1.25 to 1.50 m during the
deficit period for the pre-anthesis deficit, second
planting date treatment during 1989 ...................... 31

Figure 1.8. Relative extension growth of pre-anthesis
deficit, first planting date plants as a function of
water absorption rate at different depths during 1989....32

Figure 1.9. Relative extension growth of pre-anthesis
deficit plants as a function of relative water

absorption rate at the 0.00 m to 0.25 m soil depth

during 1988 and 1989......................... ............ 34

Figure 1.10a. Potential evaporation and measured total
water absorption from the 1.5 m soil profile during the
deficit period for the pre-anthesis deficit, first
planting date treatment during 1989 ...................... 35

Figure 1.10b. Potential evaporation and measured total
water absorption from the 1.5 m soil profile during the
deficit period for the pre-anthesis deficit, second
planting date treatment during 1989..... ....... ..........36

Figure 1.11. Leaf area accumulation for all treatments

of hybrid 3540 during 1989. The region between the
vertical dashed lines depicts the deficit period ......... 39

xi

Figure 1.12. Growth of individual leaves for all
treatments of hybrid 3540 during 1989 before (leaf 10),
during (leaf 14), and after (leaf 17) the pre-anthesis
deficit as a function of thermal time after planting.

The region between vertical dashed lines represents the
thermal time of the pre-anthesis deficit of the second
planting date, and the region between the vertical solid
lines represents the thermal time of the pre-anthesis
deficit of the first planting date.......... ............. 40

Figure 1.13a. Maximum area of individual leaves for
all treatments of hybrid 3540 during 1989.. ...... . ....... 41

Figure 1.13b. Final internode lengths for all
treatments of hybrid 3540 during 1988 .................... 42

Figure 1.13c. Final internode lengths for all
treatments of hybrid 3540 during 1989....... ............. 43

Figure 1.14a. Leaf tip number for all treatments of

hybrid 3540 during 1988 as a function of thermal time
after planting. The region between vertical dashed

lines represents the thermal time of the pre-anthesis
deficit treatment......... ....... .... ..... ... ............ 45

Figure 1.14b. Leaf tip number for all treatments of
hybrid 3540 during 1989 as a function of thermal time
after planting. The region between vertical dashed
lines represents the thermal time for the pre-anthesis
deficit of the second planting date, and the region
between vertical solid lines represents the thermal
time for the pre-anthesis deficit of the first planting

dateOOOOOOOOOOOOOOO......OOOOOOOOOOOOOO0.00.00.00.000000046

Figure 1.14c. Leaf ligule number for all treatments of
hybrid 3540 during 1989 as a function of thermal time
after planting. The region between vertical dashed

lines represents the thermal time for the pre-anthesis
deficit of the second planting date, and the region
between vertical solid lines represents the thermal

time for the pre-anthesis deficit of the first planting
date............................. ................ ........47

Figure 1.15a. Height to the top leaf ligule for all
treatments of hybrid 3540 during 1988. The region

between the vertical dashed lines depicts the deficit
period............................. ..... ..... ............ 49

Figure 1.15b. Height to the top leaf ligule for all
treatments of hybrid 3540 during 1989. The region

between the vertical dashed lines depicts the deficit
period... ..... ...................... ..... ... ............. 50

xii

Figure 1.16. Plant leaf area as a function of height
to top leaf ligule for a combination of cultivars,
planting dates, and water regimes during 1989 ............ 51

Figure 2.1a. Tasseling percentage of treatments as a
function of time for hybrid 3540 during 1989 ............. 62

Figure 2.1b. Tasseling percentage of treatments as a
function of time for hybrid 3475 during 1989....... ...... 63

Figure 2.2a. Silking percentage of treatments as a
function of time for both hybrids during 1988 ............ 64

Figure 2.2b. Silking percentage of treatments as a
function of time for hybrid 3540 during 1989 ............. 65

Figure 2.2c. Silking percentage of treatments as a
function of time for hybrid 3475 during 1989....... ...... 66

Figure 2.3a. Intact ear length of treatments for both
hybrids during 1988. ....... .... ..... . ....... ...... ....... 68

Figure 2.3b. Intact ear length of treatments for hybrid
3540 during 1989. The dashed line represents the

probable beginning date of ear appearance for the
respective treatment.. .......... .. ............. .. ........ 69

Figure 2.3c. Intact ear length of treatments for hybrid
3475 during 1989. The dashed line represents the

probable beginning date of ear appearance for the
respective treatment...................... ............... 70

Figure 2.4a. Grain filling as measured by single kernel
samples for treatments of hybrid 3540 during 1989........72

Figure 2.4b. Grain filling as measured by single kernel
samples for treatments of hybrid 3475 during 1989........73

Figure 2.5a. Grain yields, final grain weight, and
grain number for treatments of both hybrids during
1988...... ..... . ...... . .................................. 75

Figure 2.5b. Grain yields, final grain weight, and
grain number for treatments of hybrid 3540 during
1989.00.00.000000000000...... ..... O. ..... O. ..... O ........ 76

Figure 2.5c. Grain yields, final grain weight, and
grain number for treatments of hybrid 3475 during
1989.00.00.00000000000......OOOOOOOOOO OOOOOOOOOOOOOOOOOOO 77

xiii

Figure 2.6a. Grain size distribution of single ears at
harvest for the hybrid 3540 I P1 treatment during
1989...... ........ O ...... 0.0.00 0000000000 O OOOOOOOOOOOOOOO 79

Figure 2.6b. Grain size distribution of single ears at
harvest for the hybrid 3540 PAD P1 treatment during

198900..0......000000000000000...00.00000000000000000000.80

Figure 2.6c. Grain size distribution of single ears at
harvest for the hybrid 3540 PAD P2 treatment during
1989.....0.....00.00 ...... 00.0000... ..... 0... ............ 81

Figure 2.6d. Grain size distribution of single ears at
harvest for the hybrid 3475 I P1 treatment during

1989....0.00...00....0.00.0000.00000.0.....0..0.00..O....82

Figure 2.6e. Grain size distribution of single ears at
harvest for the hybrid 3475 PAD P1 treatment during
1989. ..... . OOOOOOOOOOOOOOOOOOOOOOOOOO 0 OOOOOOOOOOOOOOOOOOO 83

Figure 2.6f. Grain size distribution of single ears at
harvest for the hybrid 3475 PAD P2 treatment during
1989..0...0...00 0000000000000 00.0.0....00.0 ..... 0. ....... 84

Figure 3.1a. Above ground biomass for treatments
during 1988. The region between the vertical dashed
lines depicts the deficit period.................... ..... 95

Figure 3.1b. Above ground biomass for treatments
during 1989. The region between the vertical dashed
lines depicts the deficit period.........................96

Figure 3.2a. Daily solar radiation at the research
Site during 1988......00..000.0000.0.0.0....000 .......... 97

Figure 3.2b. Daily solar radiation at the research
site during 1989 ........ .. ........ ...

..... 000000....0000098
Figure 3.3a. Leaf biomass for treatments during 1989.
The weight includes sheathes. The region between the
vertical dashed lines depicts the deficit period. ....... 100

Figure 3.3b. Stem biomass for treatments during 1989.
The weight includes the tassel. The region between the
vertical dashed lines depicts the deficit period ........ 101

Figure 3.3c. Husk, silk, and cob biomass for

treatments during 1989. The region between the
vertical dashed lines depicts the deficit period ........ 102

xiv

Figure 3.3d. Grain biomass for treatments during
1989. The region between the vertical dashed lines
depicts the deficit period..............................103

Figure 3.4. Above ground crop growth rate (CGR) for
treatments during 1989. The region between the
vertical dashed lines depicts the deficit period.. ...... 105

Figure 3.5. Leaf area index (LAI) for treatments
during 1989. The region between the vertical dashed

lines depicts the deficit period ............. . .......... 106
Figure 3.6. Above ground net assimilation rate (NAR)

for treatments during 1989. The region between the
vertical dashed lines depicts the deficit period ........ 108

Figure 3.7a. Leaf rolling for leaves 10, 11, and 12
of pre-anthesis deficit plants of the first planting
date during 1989...0....0000......0.0.00.......0.. ...... 110

Figure 3.7b. Leaf rolling for leaves 10, 11, and 12
of pre-anthesis deficit plants of the second planting
dateduring1989.00.00.000000000000.0.00.0...00.0.000000111

Figure 3.8a. Minirhizotron root observations for
irrigated and pre-anthesis deficit plants on DOY 166 in
1988. This was before the deficit period.......... ..... 112

Figure 3.8b. Minirhizotron root observations for
irrigated and pre-anthesis deficit plants on DOY 182 in
1988. This was during the deficit period ............... 113

Figure 3.8c. Minirhizotron root observations for
irrigated and pre-anthesis deficit plants on DOY 203 in
1988. This was after the deficit period. ............... 114

Figure 3.9. Above ground plant nitrogen content (%)
and distribution in leaves, stems, and ears for all
treatments on DOY 212 in 1989................. .......... 117

Figure 3.10. Grain nitrogen content (%) on DOY 227,
DOY 249, and at harvest (DOY 270) for all treatments in
1989...00..0..0..00.0 00000000000000 0.00.... ............. 118

Figure 4.1. Soil water content of a Spinks soil at
different depths after saturation followed by three days
drainage and after more than forty days of drying by a

corn crop. . . 0 0 . . . . O . 0 . . 0 0 0 0 O . . O O . . . . . . . . 0 . . 0 O 0 . 0 0 0 0 0 O 0 O O 128
Figure 4.2. Irrigation amounts applied to treatment 1
during 1987 O 0 0 . O O . 0 . 0 0 O 0 0 0 . 0 0 O O O 0 0 0 . O . O 0 O 0 0 0 0 . ....... 0 0 O 1.30

Figure 4.3. Irrigation amounts applied to treatments
during 1988. The region between vertical dashed lines
represents the period when no water was applied to

flowering deficit (FD) treatment ........... . ............ 132
Figure 4.4. Silking percentage of treatments as a
function of time during 1988.. ......... ............ ..... 137
Figure 4.5. Intact ear length of treatments as a

function of time during 1988............................138

Figure 4.6a. Water absorption rates at depths of 0.00

to 0.25 m, 0.25 to 0.50 m, and 0.50 to 0.75 m during the
deficit period for the flowering deficit treatment

during 1988. ......... . .................................. 140

Figure 4.6b. Water absorption rates at depths of 0.75

to 1.00 m, 1.00 to 1.25 m, and 1.25 to 1.50 m during the
deficit period for the flowering deficit treatment

during 1988............. ................................ 141

Figure 4.7. Potential evaporation and measured total
water absorption from the 1.5 m soil profile during the
deficit period for the flowering deficit treatment

during 1988.............................................142

Figure 5.1. Soil water content of a Spinks soil at
different depths after saturation followed by three days
drainage and after more than forty days of drying by a
corn crop........ ....................................... 154

Figure 5.2. Thermal time accumulation during 1989.
There were two planting dates (P1 and P2). Units were
calculated using 8 C as base temperature...............156

Figure 5.3. Irrigation amounts applied to treatments.

The region between vertical dashed lines represents the
period when no water was applied to grain filling

deficit (GFD) treatments............ ...... . ............. 157

Figure 5.4a. Water absorption rates at depths of 0.00

to 0.25 m, 0.25 to 0.50 m, and 0.50 to 0.75 m during the
deficit period for the grain filling deficit, first
planting date treatment........ ........... . ............. 163

Figure 5.4b. Water absorption rates at depths of 0.75

to 1.00 m, 1.00 to 1.25 m, and 1.25 to 1.50 m during the
deficit period for the grain filling deficit, first
planting date treatment......................... ........ 164

xvi

Figure 5.5a. Water absorption rates at depths of 0.00

to 0.25 m, 0.25 to 0.50 m, and 0.50 to 0.75 m during the
deficit period for the grain filling deficit, second
planting date treatment.................................165

Figure 5.5b. Water absorption rates at depths of 0.75

to 1.00 m, 1.00 to 1.25 m, and 1.25 to 1.50 m during the
deficit period for the grain filling deficit, second
planting date treatment.... ............................. 166

Figure 5.6. Potential evaporation and measured total
water absorption from the 1.5 m soil profile during the
deficit period for the grain filling deficit
treatments.................. ......... . .................. 167

Figure 5.7a. Leaf area index (LAI) for treatments of
hybrid 3540. The region between the vertical dashed

lines represent the water deficit period, and the V

marks silking date of irrigated control.................168

Figure 5.7b. Leaf area index (LAI) for treatments of
hybrid 3475. The region between the vertical dashed

lines represent the water deficit period, and the V

marks silking date of irrigated control ....... ..........169

Figure 5.8a. Above ground biomass for treatments of
hybrid 3540. The region between the vertical dashed
lines represents the water deficit period, and the V
marks silking date of irrigated control.................171

Figure 5.8b. Above ground biomass for treatments of
hybrid 3475. The region between the vertical dashed
lines represents the water deficit period, and the V
marks silking date of irrigated control............ ..... 172

Figure 5.9a. Above ground crop growth rate (CGR) for
treatments of hybrid 3540. The region between the
vertical dashed lines represents the water deficit

period, and the V marks silking date of irrigated
control.... .............. .............. ...... ...... ..... 173

Figure 5.9b. Above ground crop growth rate (CGR) for
treatments of hybrid 3475. The region between the
vertical dashed lines represents the water deficit

period, and the V marks silking date of irrigated
control. ......... . ......... . .................. . ......... 174

Figure 5.10a. Grain biomass for treatments of hybrid
3540. The region between the vertical dashed lines
represents the water deficit period................ ..... 176

xvii

Figure 5.10b. Grain biomass for treatments of hybrid
3475. The region between the vertical dashed lines
represents the water deficit period.....................177

Figure 5.11a. Whole plant grain growth rate (GGR) for
treatments of hybrid 3540. The region between the
vertical dashed lines represents the water deficit
period............................................. ..... 178

Figure 5.11b. Whole plant grain growth rate (GGR) for
treatments of hybrid 3475. The region between the
vertical dashed lines represents the water deficit
period..... ......... ............................... ..... 179

Figure 5.12a. Crop growth rate (CGR) to grain growth
rate (GGR) ratios for treatments of hybrid 3540 during
linear grain filling00000.000....000000.0.00.00.00.00000182

Figure 5.12b. Crop growth rate (CGR) to grain growth
rate (GGR) ratios for treatments of hybrid 3475 during
linear grain filling ............... . .................... 183

Figure 5.13a. Single kernel weights for treatments of
hybrid 3540. Samples were from the middle of the ear.

The region between the vertical dashed lines represents

the water deficit period................................185

Figure 5.13b. Single kernel weights for treatments of
hybrid 3475. Samples were from the middle of the ear.

The region between the vertical dashed lines represents

the water deficit period ..... ............ ............... 186

Figure 5.14a. Grain filling rate of single kernels for
treatments of hybrid 3540. Samples were from the middle

of the ear. The region between the vertical dashed

lines represents the water deficit period.. ............. 187

Figure 5.14b. Grain filling rate of single kernels for
treatments of hybrid 3475. Samples were from the middle

of the ear. The region between the vertical dashed

lines represents the water deficit period....... ........ 188

Figure 5.15a. Grain yields, final grain weight, and
final grain number per ear for treatments of hybrid
3540......0OOOOIOOOOOO0.0.00.00.00.0000000. ..... O ....... 190

Figure 5.15b. Grain yields, final grain weight, and

final grain number per ear for treatments of hybrid
3475.00...000..00000.0.0.0....0...0...0. OOOOOOOOOOOOOOOO 191

Figure 5.16a. Grain size distribution on single ears at
harvest for the hybrid 3540 I P1 treatment .............. 192

xviii

Figure 5.16b. Grain size distribution on single ears at
harvest for the hybrid 3540 GFD P1 treatment ............ 193

Figure 5.16c. Grain size distribution on single ears at
harvest for the hybrid 3540 GFD P2 treatment ..... . ...... 194

Figure 5.16d. Grain size distribution on single ears at
harvest for the hybrid 3475 I P1 treatment..............195

Figure 5.16e. Grain size distribution on single ears at
harvest for the hybrid 3475 GFD P1 treatment..... ....... 196

Figure 5.16f. Grain size distribution on single ears at
harvest for the hybrid 3475 GFD P2 treatment ............ 197

xix

INTRODUCTION

Record yields of important agronomic crops are three to
seven times greater than those obtained on average, even in
more developed agricultural regions (Boyer, 1982; Ritchie,
1983). Diseases and insects account for only a small fraction
of the deviation from the high yields, whereas physicochemical
problems make up 70 % of the difference (Boyer, 1982). Among
the environmental factors responsible for drastic crop yield
reductions, drought, or water deficit conditions, is the main
one. Boyer and McPherson (1975) stated that no other factor
limits grain yield so extensively and unpredictably. Water
deficits are not confined to dry regions. Decker (1983)
reminded that drought is not a rare event even in humid
regions, and Ritchie (1983) viewed an important avenue for
world. wide improvement. of“ crop jproductivity' was through
reduction of short drought periods in humid regions.

Decker (1983) suggested three ways of defining drought
with a definition based on; 1) climatic expectation, 2) long
term.impact of "dry" weather such as reservoir water levels or
yields of major crops, and 3) dryness of agricultural soils

using a pre-set value relating to plant available water. The

2

first two definitions have been used in a broad sense to
describe production limitations of rather large agricultural
regions, however, as Ritchie (1983) pointed out these
definitions are restricted in making resource and management
decisions. The third definition approaches that needed for
decisions on state, county, or even individual grower levels,
yet it is important only as related to weather and yields.
Functional crop 'models attempt. to incorporate all three
aspects such that management and resource decisions can be
made on any desired level. However, these models are useful
only if they can. predict yields reasonably’ well for a
diversity of environmental conditions. This requires the
support of continued research into the mechanisms of how
plants respond to water deficits.

Solving production limitations due to water deficiencies
in more humid regions is not as simple as a mass change to
irrigated agriculture in these regions, especially in the
United States. Ritchie (1983) reminded that principles of
humid region irrigation are different than those of drier
regions. He suggested that technology has to be sought that
minimizes excess water movement through the soil which lends
to chemical leaching, while maintaining a favorable nutrient
and water supply in the root zone. While economic incentives
have dominated U.S. production agriculture in the past, an age
where this may no longer be true is likely eminent. There is

a growing concern for the environment as well as maintaining

3
production, and this poses great challenges. Boyer (1982)
remarked, "Responding effectively to mounting world food
demands, economic pressures, and the need for conservation
are dilemmas for farmers and legislators alike." One could
add that pressure has been put on agricultural scientists as
well to seek ways of maintaining this balance.

Michigan is a state which holds potential for increased
crop production with supplemental irrigation. According to
Lucas and Vitosh (1978), Michigan has the lowest summer
rainfall of any state east of the Mississippi River. They
reasoned there is about a 40 % probability of at least a mild
drought occurrence during the months of June, July, and
August" Their’ definition ‘used. for' drought incorporated
definitions one and three of Decker (1983) as discussed
previously; Soils ranging in texture from sandy to sandy loam
were depicted by Lucas and Vitosh (1978) as running out of
water in 4 to 14 days under crop production. They indicated
75 % of the plant available water in the upper 0.9 m of soil
as the threshold depletion value. Corn grain yields were
estimated to increase as much as 90 % to 300 % under irrigated
conditions on these soils.

Algozin et al. (1988) reported about 162,000 hectares of
irrigated cropland in Michigan with about 50 % of this being
dedicated to corn production. Their work analyzed irrigation
strategies based on yield, as well as water use and energy

consumption. Based on a somewhat crude definition of water

4

use efficiency (WUE) which is defined as unit of economical
yield.per unit of water applied (Bolton, 1981), the results of
Algozin et a1. (1988) demonstrated that irrigation application
rates of 6 mm, 13 mm, and.25 mm.per application.had.WUE values
of 69, 65, and 59 kg mmq, respectively, for the supplemental
water. Therefore, the smaller volume but more frequent
irrigation applications were the most efficient in terms of
water and energy as opposed to traditional applications of 25
mm or more. While this analysis was based on simulated
results using a crop model, their results were within the
range of real values which they reported.

The aim of the scenario presented by Algozin et a1.
(1988) was to encourage irrigation scheduling on the basis of
profit and efficiency instead of maximum yields. Field
research often leans toward.the latter'point, therefore, there
exists the need for exploring yield compromises in exchange
for reduced applications of water. Begg and Turner (1976)
discussed several important aspects to consider when studying
water deficit effects on plants, and these would fit well in
to the planning of irrigation strategies as well. An
increased understanding of crop water deficits is a
prerequisite to achieving the previously mentioned goals of
maintaining production and resources. One of the 'most
important factors to consider is the crop growth stage.
Ludlow and Muchow (1988) stated that management and cultivar

selection should match crop phenology with expected water

5
supply in the most efficient way. They presented several
avenues to explore in improving crop production per unit of
given water under conditions prone to either terminal or
intermittent drought. Those given for intermittent drought
regions included leaf growth, water extraction, developmental
patterns, and hybrid differences under deficit conditions.

Shaw (1983) reviewed yield reductions of corn due to
water deficits. A general concept presented showed potential
yield reductions due to a water shortage were as much as 3 %
per day of stress when it occurred 30 days either side of
silking. A more critical time from a few days prior to
silking to 10 to 12 days past could result in yield losses as
great as 8 % per day of stress. These broad concepts lend
areas of focus for discerning crop water needs, however, it
is difficult to incorporate these ideas into the more careful
management strategies that have been presented in the
preceding discussion. Begg and Turner (1976) suggested that
sensitivity of crops to stress at any growth stage varies and
depends on degree, duration, and timing of the stress.

More detailed investigations as to whole plant responses
to water deficits at different growth stages are needed,
especially at the field level. Several investigations in
controlled environments with container grown plants have been
used for this purpose also. MUch of our understanding of
plant water relations has evolved from container experiments,

however, the information gained must eventually be proven

6

useful under field environments. Ritchie (1973) emphasized
differences between container grown plants and those in the
field. He viewed that a major difference between the two
environments was that of an unrealistic rooting volume for
container plants. Begg and Turner (1976) supported this idea
as well. They surmised that water deficits developed so
rapidly when containers were used that plant adaption to
stresses could not occur as it might in the field. Also, Shaw
(1983) indicated that under field conditions fertility stress
is often combined with water deficit conditions as nutrients
are concentrated in the surface soil layers which are often
dry.

The objective of this research was to investigate whole
plant responses of corn to intermittent water deficits at
different stages of growth. under field conditions. .An
auxiliary’goal is to utilize the results to lend understanding
and improvement to the prediction of corn performance under
deficit conditions using crop models. The integration of this
knowledge with that of experiments being conducted by others
will help in developing the needed decision and management
tools to achieve sustainable, productive, and profitable

farming of corn in more humid regions such as Michigan.

LIST OF REFERENCES

Algozin, K.A., V.F. Bralts, and J.T. Ritchie. 1988.
Irrigation strategy selection based on crop yield, water, and
energy use relationships: A Michigan example. J. Soil Water
Conservation 43: 428—431.

Begg, J.E. and N.C. Turner. 1976. Crop water deficits. Adv.
Agron. 28:161-217.

Bolton, F.E. 1981. Optimizing the use of water and nitrogen
through soil and crop management. In Monteith and Webb (ed.)
Soil water and nitrogen in Mediterranean-type environments.
pp. 231-247. Martinus Nijhoff/Dr. W. Junk Publishers. The
Hague, The Netherlands.

Boyer, J.S. 1982. Plant productivity and environment.
Science 218: 443-448.

Boyer, J.S. and H.G. McPherson. 1975. Physiology of water
deficits in cereal crops. Adv. Agron. 27: 1-23.

Decker, W.L. 1983. Probability of drought for humid and
subhumid regions” .IQIRaper and Kramer (ed.) Crop reactions to
water and temperature stresses in humid, temperate climates.
pp. 11-19. Westview Press. Boulder, Colorado.

Lucas, R. and M. Vitosh. 1978. High corn yields with
irrigation. Cooperative Extension Service Bulletin E-857.
Michigan State University, East Lansing, Michigan.

Ludlow, M.M. and R.C. Muchow. 1988. Critical evaluation of
the possibilities for modifying crops for high production per
unit of precipitation» .IQIBidinger‘and.Johansen (ed.) Drought
research priorities for the dryland tropics. pp. 179—211.
International Crop Research Institute for the Semi-Arid
Tropics. Patancheru, India.

Ritchie, J.T. 1973. Influence of soil water status and
meteorological conditions on evaporation from a corn canopy.
Agron. J. 65: 893-897.

8

Ritchie, J.T. 1983. Reduction of stresses related to soil
water deficit. In Raper and Kramer (ed.) Crop reactions to
water and temperature stresses in humid, temperate climates.
pp. 329-340. Westview Press. Boulder, Colorado.

Shaw, R.H. 1983. Estimates of yield reductions in corn
caused by water and temperature stress. In Raper and Kramer
(ed.) Crop reactions to water and temperature stresses in
humid, temperate climates. pp. 49-65. Westview Press.
Boulder, Colorado.

CHAPTER 1

PRE-ANTHESIS SOIL WATER DEFICIT EFFECT ON CORN (ZEA MAXS L.).
I. VEGETATIVE GROWTH AND DEVELOPMENT

A§§IBAQI

An increased interest in scheduling irrigation in more
humid regions in order to conserve water and prevent ground
water contamination while maintaining favorable crop
production lends to the necessity of determining effects of
intermittent water deficits on crop growth. A plausible
growth stage for reduced irrigation applications is pre-
anthesis. Research was conducted in Michigan during 1988 and
1989 utilizing a rain shelter to control water regimes in a
field environment. Objectives were to determine immediate and
subsequent responses of corn to periods of soil water deficit
prior to anthesis. An 18 to 21 day period without water on
a sandy soil was initiated as the 8th or 9th leaf emerged from
the whorl of plants for two corn hybrids. Results of
vegetative growth and development reported here indicated

plant extension growth was highly correlated with water

10
absorption from the upper 0.25 m of soil. When relative water
absorption (actual divided by potential maximum) from the
surface soil layer fell to 85 % to 90 96, relative plant
extension growth of deficit plants declined linearly reaching
zero at 25 96 to 30 % relative water absorption. The reduction
in extension growth resulted in delayed leaf tip emergence,
reduced leaf area, and shortened internodes. Height to the
top leaf ligule was determined to be a much less laborious
plant measurement than individual leaf measurements, and it
proved to be just as useful in evaluating extension growth and
leaf area to some degree. Additional results on reproductive
growth and development and on biomass and nitrogen
accumulation and partitioning are presented in companion

papers.

INTRODUCTION

There has been an increasing interest in scheduling
irrigation applications in order to conserve water and to
prevent excess water movement through the soil which might
lend to ground water contamination. This has been especially
true in more humid regions where irrigation is supplemental,
and the soil profile is often fully recharged at the beginning
of the growing season. A corn growth stage plausible for
reduced water applications is pre-anthesis, as vegetative

water deficits have been found to be less detrimental to final

11

yield than flowering and grain filling water deficits
(Claassen and Shaw, 1970: Denmead and Shaw, 1960: Grant et
al., 1989: Robins and Domingo, 1953). Nevertheless, leaf and
stem elongation have been determined to be among the most
sensitive plant processes to shortages of water (Hsiao, 1973) ,
and these processes have been shown to be reduced as plant
water status declines (Acevedo et al., 1979: Boyer, 1970;
Michelena and Boyer, 1982: Sharp and Davies, 1979). If the
goal of reducing irrigation applications is to be met, pre-
anthesis water deficits need to be examined more carefully to
circumscribe the overall influence on plant growth and yield,
and to improve the predictability of this influence.

Agronomically, soil water has been a frequently measured
parameter. Grant et al. (1989) indicated that the status of
soil water was more predictable and obtainable than that of
plants on a field level, and Ludlow (1987) suggested that the
lack of a unique relationship between plant water potentials
and physiological processes has led to the use of soil water
status to simulate shoot performance in many crop growth
models. Recent experiments have demonstrated stomatal
conductance and leaf and stem elongation were reduced in
response to soil drying before there was any appreciable
influence on shoot water status (Blackman and Davies, 1985:
Davies et al., 1986: Gollan et al., 1986; Schulze, 1986).
Additional information on the dynamics of soil water and its

influence on plant growth processes in the field is needed.

12

Field water deficit experiments are difficult to conduct
in humid regions due to the untimeliness of rain. This is
especially true when the study of drought during a specific
growth stage is desired. IRain shelters have aided in reducing
the risk of rain interfering with water deficit experiments
(Foale et al., 1986; Upchurch et al., 1983). This, along with
controlled water applications, can provide judicious
scheduling of crop water supply (NeSmith et al., 1990). The
objectives of this research were to utilize a rain shelter to
determine the immediate and subsequent effects of corn growth
and development in response to a pre-anthesis soil water
deficit in a field environment. Results of vegetative growth
and development are reported here, while results of
reproductive growth and development, and of biomass and
nitrogen accumulation and partitioning are reported in

companion papers.

flfIEBIALé AND METHODS

This research was conducted during 1988 and 1989 at the
Kellogg Biological Research Station near Kalamazoo, Michigan,
USA. Corn was grown in an area that could be covered by a
rain shelter. This facility has been described elsewhere by
Martin et al. (1988). The soil was a Spinks sand (sandy,
mixed, mesic Psammentic Hapludalf). Figure 1.1 illustrates

the water content of the soil profile after near saturation

l3

 

 

0.25
A ‘ — DrySoil
T It -- Droined Soil
g 0.20‘
to .
E .
V 0.15-
., .
CI .
o .
‘E .
O 0.10-
L) .
3 1
+6 .
3 °-°5‘1
7'5 I
.m .
0.00 Ut1i'fitfir11fi1 t',~"fj'

 

 

 

0.0 0.5 1.0 -115. 2.0 2.5
Soil Depth (m)

Figure 1.1. Soil water content of a Spinks soil at different
depths after saturation followed by three days drainage and
after more than forty days of drying by a corn crop.

14
followed by three days of drainage and after more than forty
days of drying by a corn crop with no additions of wateru The
rain shelter did not cover plots from September to April each
year, and as a result the soil water profile was near the
drained equilibrium status at the beginning of the growing
season because of snow and rain.

Due to limited space at the rain shelter site, the first
year experiment consisted of a single replication for each
treatment. A completely randomized split-plot experimental
design was used in which water regime was the main plot and
corn cultivar was the sub-plot. Main plot size was 4.3 m x
6.2 m. Pioneer corn hybrids 3540 and 3475 were planted at a
higher than desired density on 5 May (day of year, DOY, 126)
in 0.71 m rows at a depth of 0.05 m. These hybrids were chosen
because there had been some observed differences between them
in response to drought during certain years but not others.
Part of this investigation was to determine potential reasons
for such variability. Emergence occurred on 15 May, and
plants were thinned to a population of 7.9 plants In.2 on 25
May. Fertilizer applications were 150 kg ha.1 K on 20 April,

60 kg ha1

N on 25 May, 300 kg ha'1 P and 160 kg ha.1 N on 6
June, and 75 kg ha.1 N on 15 July.

In 1989, the experiment was enlarged to include two
replications for each treatment. There were two planting

dates“ The reason for this was that there was a difference in

leaf number of one leaf between the two cultivars during 1988,

15
as well as a two to three day difference in tasseling and
silking. It was hypothesized that this could be linked to
some of the differences in observed responses to drought, as
plants would.have been at different developmental stages (e.g.
hybrid 3475 flowered 2 to 3 days before hybrid 3540). It was
planned that around 50 degree days.(°Cd) would elapse between
the first and second planting dates to provide a thermal time
separation so that the two genotypes would end their
vegetative growth nearer the same time. This was to provide
hybrid comparisons of plants nearer in development (i.e. the
second planting date of hybrid 3475 would be similar in
development to the first planting date of hybrid 3540). Water'
deficits were imposed at the same time for both planting
dates. Plot size, row width, and seeding depth were the same
as in 1988. Main plots were water regime and planting date,
\—-~.
and again sub-plots were corn cultivars. Planting dates were
3 May (DOY 123, this will be referred to as P1 indicating
first planting) and 17 May (DOY 137, this will be referred to
as P2 indicating second planting) which were separated by 64
°Cd (Figure 1.2). Emergence occurred on 18 May and 25 May,
and plants were thinned on 26 May and 30 May for P1 and P2,
respectively. Fertilizer was applied.at planting at a rate of
63 kg ha1 N, 230 kg ha.1 P, and 63 kg ha.1 K.' Additional
fertilizer applications for P1 and P2 were 96 kg ha'1 N on 1*

1

June, 53 kg ha. N on 23 June, and 45 kg ha.1 N on 20 July.

Weeds were controlled manually during both years.

16

2000

 

d--- 1988
1800-; 1939p1
: -- 1989P2
16001
1400{
12005
1000{
800{
600{
400{
200{

Thermal Time After Plonting (OCd)

 

 

 

 

q ..'
O ijl‘rit' ITT‘IIIIIIIj "j'U‘Ilr‘Ul'

120 140 100 180 200 220 240 260 280
Day of Year

Figure 1.2. Thermal time accumulation during 1988 and 1989.

There were two planting dates (P1 and P2) during 1989. Units
were calculated using B‘Tras base temperature.

17

Water regimes were similar for both years. There were
two treatments, an irrigated control (I) and a pre-anthesis
water deficit (PAD). Water applications were the same for
treatments except during the deficit period (Figures 1.3a and
1.3b). The PAD began near the appearance of the tenth leaf
tip and ended before tassel emergence of the irrigated
control. The deficit was 21 days (300 °Cd) in 1988 and 18
days (265 °Cd) in 1989.

Sample plants for nondestructive measurements of leaf
area and extension growth were selected one month after
planting. Eight and four plants per plot were tagged and
monitored throughout the growing season during the first and
second year, respectively. During both years leaf extension
was determined by measuring the growth of upper leaves that
did not have a visible ligule. Relative leaf extension was
calculated for the water deficit plants by dividing their
extension rate by that of the control plants. Height from
the soil surface to the top leaf ligule was measured several
times weekry. Relative extension was also calculated from
this measurement for water deficit plants by dividing by the
rate of control plants. The PAD P2 plants during 1989 were
compared to P2 control plants, as there was a treatment in
another experiment with the same planting date which was
irrigated until after silking. Final internode lengths were

measured on plants at the end of the growing season.

l8

 

 

1888

illtl‘tl1lii'l.l

|Il|1|t||lu|i1lqll|ltlu

l'lll|ll|||lllu
'I'll‘ll'll

illilllltllI-Illllllllu'l

lill't‘l‘l"

 

Illllfll.’
I'Illlilllll‘l

 

140 160

120

 

d‘d‘ddd‘d-I‘ddddd‘I-d‘dd_‘ddd.d‘dq-iddd-(GG‘CdIIIdC‘I

.-
50505050
fiwfiw332211

AEEV E3088. c0509:

Day of Year

Irrigation amounts applied to treatments during

The region between vertical dashed lines represents the
period when no water was applied to pre-anthesis deficit

treatments.

Figure 1.3a.
1988.

19

 

280

I101

260

 

illitlllllllllllllllilll‘ld

llilllllllli'll'l'lllll

1989

l'ltlllllllll

220

1I1I'11IIIII'IIIlIII'lIIIlII-Inl

lllllllllllll."|||'ll|

200 "

Day of Year

Itlttltlll'litiluilOIIIa-‘llllll

Ihfli
Pub!
l
1
1
11
11
.1
11
11
1
1
11
11
11
11
I
1-0

lllllllllliltill'llllll1ll1'lsrtvl'lllrll"

 

140

  
  

 

120

 

“-‘dil.ddid-11“.G‘II‘I‘IG‘Cddd“ddddddd‘q‘dflddd

505050505050
5544332211

AEEV assoc}. caboott

Irrigation amounts applied to treatments during

. The region between vertical dashed.lines represents the
period when no water was applied to pre-anthesis deficit

Figure 1.3b.
1989.
treatments.

20

During 1988, leaf appearance was determined by recording
when1a respective leaf tip was visible. In 1989, visible leaf
tip number was recorded four to six times weekly for all the
sample plants, and these values were averaged and plotted as
a function of thermal time. Leaf ligule appearance rate was
assessed similarly during the second year. Leaf area was
determined two or three times weekly during 1989, beginning

7:233“

with the fourth leaf. Leaf length, taken as the distance from
the uppermost leaf ligule to the tip of a growing leaf, was
multiplied by the maximum exposed leaf width, and 75 96 of this
product was assumed to approximate the area of an individual
leaf (see Johnson and Tanner, 1972; Linvill et al., 1978).
Leaf area was considered maximum when its respective leaf
ligule appeared.

Soil water content was measured both years using the
neutron scattering technique. Sampling was in 0.25 m
increments to a depth of 1.5 m. There was one access tube in
the center row of each sub-plot the first year and two the
second. In 1988, weekly measurements did not begin until
after the deficit treatment had been imposed. However, in
1989 measurements began shortly after planting and were taken
one or two times weekly until near physiological maturity of
the crop. The water content during the 1989 deficit period
was plotted and a line fitted through the data for each

sampled depth. The slope of this line was taken as water

 

21
absorption rate, with the assumption that upward soil water

flux was negligible.

S S ON

Figures 1.4a and 1.4b depict the water content of the
1.5 m soil profile each year in units of equivalent depth.
The soil water data were averaged for both hybrids as there
were no detectable differences between them. Similar patterns
of profile drying occurred during the two years for deficit
treatments, except that the soil was drier at the end of the
deficit period in 1988. This was primarily attributable to
a longer deficit period during the first year. Irrigated
control plots were maintained at a favorable water content
both years.

Plant extension growth declined in response to the soil
water deficits for the two hybrids similarly both years
(Figures 1.5a through 1.5c). .A 'measurable decrease in
extension of PAD plants was obtained in less than five days
after withholding water, indicating the sensitivity of this
process to shortages of soil water. The assessment of
relative extension growth from leaf length and from the height
to the top leaf ligule gave comparable results. After
irrigation resumed, extension rate of PAD plants rapidly
returned to that of I plants. Continued comparisons were not

valid after the deficit period because I plant extension

22

 

 

245': E :r HI
235' ' ' HPAD
(“A " : :
E 215-* ------------- :- ---- | ........
m ‘1 1 ..
v: 205- : ..fl,‘
‘ I 1'
g 195. : i,
é 185- : 1 :
a; 175- : E
*5 1651 g '
3 " .H
:: 155- :
o ‘ . .. .
(f) 1451 : :
135- : ‘1
‘ 1
125 .. , . 1.

 

 

 

1'1"1'r1'1"1Trrrrr"r"
120 135 150 165 180 195 210 225 240 255 270
Doyoneor

Figure 1.4a. Soil water content of the 1.5 m profile during
1988. Values are equivalent depth water. The horizontal
dashed line represents the estimated drained upper limit of
soil water, and the region between the vertical dashed lines
depicts the deficit period.

23

 

245%
2355
2253
2153
205J
1955
1853
1753
1653
1553
1455
135J

125JT. r.

120 135 '150

 

Soil Water (mm 1.5m_1)

 

 

------------.--¢-

1

I
I
I
l

 

.e,..,e.,..,..,..,r.
165 180 195 210 225 240 255 270
Doyoneor

Figure 1.4b. Soil water content of the 1.5 m profile during
1989. Values are equivalent depth water. The horizontal
dashed line represents the estimated drained upper limit of
soil water, and the region between the vertical dashed lines
depicts the deficit period.

24

 

 

 

 

c
.9
m
c
a
...:
x
Lu
0
.2
...:
2
a
at
A BothLigules
O1~ a 3475 Leaf A
‘ o 3540me
0.0 Tl! UifllUUITIIjII—IIIUV'

 

160 165, I70 175 180 185 190 195 200
Day of Year

Figure 1.5a. Relative extension growth of pre-anthesis
deficit plants during 1988 for hybrids 3540 and 3475 as
determined from leaves and from the height to the top leaf
ligule.

25

 

 

 

 

 

1.1
1.0: -------- -I---§fi- ----------------------------
0.9-
C -
.9 0.8q
2 OJL-
0 .
3'2 05‘ PAD P1
uJ 4
q, 0.5-
.2 ‘
‘9': 0.4-:
d)
a: (13:
0.2- x 3475 Ligulo
< A 3540 Ligulo
0.1- o 3475 Leaf
‘ f
0.0 ML W

160 165 170 175 180 1&5 190 195 200
Day of Year

Figure 1.5b. ‘Relative extension growth of pre-anthesis
deficit plants of the first planting date during 1989 for

hybrids 3540 and 3475 as determined from leaves and from the
height to the top leaf ligule.

26

 

 

 

 

 

1.1
1.0« -------- -I---I--- --------------------------
0.9-
1
C -
.9 0.8‘
2 0.7-
a) r
'3; 0.6-1 PAD P2
DJ .
g, 0.5-
.2 ‘
35 DEFT
Q)
a: (13:
0.2- x 3475 Ligule
1 A 3540 Ligule
0.“ a 3475 Leaf
‘ a 3540 Leaf
0.0 TUWIIIITUITfFVIITrfIUrjrrjjijjrtij 'U'U
160 165 170 175 180 185 190 195 200
Day of Year
Figure 1.5c. 'Relative extension. growth of pre-anthesis

deficit plants of the second planting date during 1989 for
hybrids 3540 and 3475 as determined from leaves and from the
height to the top leaf ligule.

27
growth had began to decline due to the approach of vegetative
maturity.

Water absorption rates at different soil depths during
the 1989 deficit period are depicted for PAD Pl plants and
PAD P2 plants in Figures 1.6a and 1.6b and Figures 1.7a and
1.7b, respectively. Shortly after the deficit began there
was a rather rapid decline in water absorption rate in the
upper 0.25 m of soil, while there was a marked increase
followed by a continuous decrease at soil depths from 1.0 m
to 1.5 m for both planting dates. Water absorption at depths
between 0.25 m and 1.0 m remained nearly steady until DOY 187.
After this, there was generally a decline in water absorption
rate at depths between 0.25 m and 0.75 m, while there was an
increase at the depth from 0.75 m to 1.0 m. These changing
water absorption rates followed changes in root growth as
reported by several researchers which indicated decreased
surface rooting and increased.root.proliferation at lower soil
depths in response to water deficits (Blum and Ritchie, 1984;
Davies et al., 1986; Hoogenboom et al., 1987: Sharp and
Davies, 1979). Taylor and Klepper (1973) noted an increased
effectiveness of deeper roots of maize as upper soil layers
dried out. .A companion paper includes root growth data of the
current experiment (NeSmith et al., 1990).

Figure 1.8 depicts the relationship between relative
extension growth and water absorption rates at different

depths for PAD P1 plants during the deficit period of 1989.

28

 

 

 

 

14
13; 0-0 0.00 to 0.25 m
o O «B—BO.25tOO.50m
w 0 12-
c, o ‘H 0.50 to 0.75 m
D: F. ”- PAD P1
c L
.9 :10.
‘é" 9:
8' 81
o d
2 P 71
to 6i
3' 5«
o E «
i: C) 4:
4410 34
8 e 9
o 2‘
a: V 1.
0‘

 

 

 

TT'rjrfiT‘1'1'1T1'rj
175 177 179 181 183 185 187 189 191 193 195
Day of Year

Figure 1.6a. Water absorption rates at depths of 0.00 to
0.25 m, 0.25 to 0.50 m, and 0.50 to 0.75 m during the deficit
period for the pre-anthesis deficit, first planting date
treatment during 1989.

29

 

 

 

14
13; e—o 0.75t01.00 m
a) O . a—a 1.00t01.25 m
*5 8 ‘2: H 1.25 to 1.50m
c d
o X 10+
23," 9.
e. -
C) )‘ 8‘
(D o 7‘
.0 '0 "
< u
L.") 6-
0 I 5.:
...1
o E -
g o 4-
+4” 3- "‘
8 E :
o 2
[K V 1. = . 9
ol ‘ ‘ ‘

 

 

‘ ' I ' I ' I ' I ' I ' F' I j I ‘
175 177 179 181 183 185 187 189 191 193 195
Day of Year

Figure 1.6b. Water absorption rates at depths of 0.75 to
1.00 m, 1.00 to 1.25 m, and 1.25 to 1.50 m during the deficit

period for the pre-anthesis deficit, first planting date
treatment during 1989.

30

 

14
13; (9-9 0.00 to 0.25 m
o O lo—aO.25toO.50m
*5 8 12‘H0.50t00.75m
Cr .— 11.. PAD P2
c: .I
.9 :10‘
8v- 91
8' 8:
.o 8 7-
< .
L."7 61
0' 5_
+1
0 E <
3 o 4j
aura 3-
o .
8 E 2-
V ..
1-
D

 

 

 

’ I ' I r I fl I ' T ' I ' I r I 1 I ‘
175 177 179 181 183 185 187 189 191 193 195
Day of Year

Figure 1.7a. Water absorption rates at depths of 0.00 to
0.25 m, 0.25 to 0.50 m, and 0.50 to 0.75 m during the deficit
period for the pre-anthesis deficit, second planting date
treatment during 1989.

31

 

 

14
1310-0 0.75to1.00 m
o o -o—a1.00to 1.25m
‘5 8 12'jm—e1.25to1.50m
m P 11_ PAD P2
c J
.9 :10.
‘9' 9‘-
8' 8‘.
.o S 7-
< 6‘
L") 1
3| 5-
o E 4
g 0 4'1
44") 3-1
8 E j
o 2
a: V 1.
O:

 

 

 

 

' I r T v I ' 1 ' r ' I r I ""'T"""“
175 177 179 181 183 185 187 189 191 193 195
Day of Year

Figure 1.7b. Water absorption rates at depths of 0.75 to
1.00 m, 1.00 to 1.25 m, and 1.25 to 1.50 m during the deficit

period for the pre-anthesis deficit, second planting date
treatment during 1989.

32

 

   

 

H 1.50 m
v—v 1.25m
x—x 1.00 m
H 0.75 m
8-9 0.50 m

(9—0 0.25 m ‘
l U I I 1 I ‘ Y I I l r I ‘U 1 fir I 1 1 1

Relative Extension

 

 

 

OOO'T‘
0123456789101112

Root Water Absorption Rate

(cm?) cm—3 day-.1) x 1000

Figure 1.8. Relative extension growth of pre-anthesis
deficit, first planting date plants as a function of water
absorption rate at different depths during 1989.

33

There was little correlation with any depth other than the
0.0 m to 0.25 m increment. Combinations of the first two
depths and all depths did not correlate better than the first
depth alone. Relative water absorption rate was calculated
by dividing the respective rate by the maximum rate measured.
Relative extension growth for PAD plants from both years was
plotted as a function of the relative water absorption rate
from the 0.00 m to 0.25 m soil layer (Figure 1.9). Relative
extension growth declined linearly when relative water
absorption fell to 0.85 to 0.90 and approached zero at
relative water absorption values of 0.25 to 0.30. Rosenthal
et al. (1987) studied relative extension rates of container
grown cotton and grain sorghum leaves in response to decreases
in plant available water (PAW). They observed rapid, near
linear'decreases in extension growth as PAW’of the entire soil
volume fell from 50 % to 0 %.

Calculations of total absorption from the 1.5 m profile
demonstrated there was enough water to meet transpiration
demand at least until DOY 183, and probably beyond this from
water below the 1.5 m depth (Figures 1.10a and 1.10b).
Therefore, the influence of soil drying on extension growth
was not due to insufficient water for transpiration. Other
investigators have shown that leaf growth was decreased under
deficit conditions before any appreciable influence on

transpiration was observed (Meyer and Green, 1980; Rosenthal

et al., 1987).

34

1.1
1.0-e ...................................
0.9:
0.8;
0.7;
0.6:-
0.53
0.4;
0.3;
0.21

 

Reiotive Extension

 

. A PAD 1988
0.1-I o a PAD P2 198i

‘ A o PAD P1 198
0.0

..j . . . . ...,.,..
0.0 0T1 01.2 oi: oil. ois 036 037 0.8 0.9 1.0 1.1

 

 

Relative Water Absorption Rate

Figure 1.9. Relative extension growth of pre-anthesis deficit
plants as a function of relative water absorption rate at the
0.00 m to 0.25 m soil depth during 1988 and 1989.

35

 

‘ o-o Potential
«5‘ 9- H Measured PAD P1

Evaporation Rate (mm doy

 

 

 

. . . . . . 1 . , . , . . .
1115 157 159 181 183 185 187 189 191 193 195
Day of Year

Figure 1.10a. Potential evaporation and measured total water
absorption from the 1.5 111 soil profile during the deficit

period for the pre-anthesis deficit, first planting date
treatment during 1989.

36

 

o—o Potential
9- H Measured PAD P2

)

-

Evaporation Rate (mm day

011‘1'11111‘1rl'1'1'
175177179181183185187189191193195

 

 

 

Day of Year

Figure 1.10b. Potential evaporation and measured total water
absorption from the 1.5 111 soil profile during the deficit

period for the pre-anthesis deficit, second planting date
treatment during 1989.

37

The idea of a root-to-shoot signal in response to soil
drying has been the subject of several recent research reports
and reviews (Blackman and Davies, 1979; Davies et al., 1986:
Gollan et al., 1986; Schulze, 1986; Turner, 1986). The exact
signal responsible for modified shoot behavior has not been
identified, however, candidates have included abscissic acid
and cytokinins as well as other unknown growth substances.
Davies et al. (1986) indicated that further investigations
were needed in this area, as soil drying can reduce root
supply of many substances, including plant nutrients. They
proposed a complex signal involving several chemical
compounds. The current study seems to support the idea of a
signaled response of soil surface drying. Results of nitrogen
uptake presented in a companion paper (NeSmith et al., 1990)
indicated this may have been linked to some of the growth
reductions reported here.

According to Barlow (1986), under severe water deficit
conditions expansion growth of plants ceases and osmotic
adjustment serves to ensure survival of meristematic tissue.
He proposed this plant adaption to the stress as a means by
which young leaves remain viable while suppressing growth.
This osmotic adjustment and halting of growth would require
continued water absorption. The relationship between
extension growth and water absorption in Figure 1.9 tends to
support this, as extrapolation indicated extension growth

would have ceased before water absorption.

38

The influence of the reduced leaf extension rates during
1989 on leaf area expansion is depicted in Figure 1.11.
There were no treatment differences between hybrids, and
results for only one hybrid (Pioneer 3540) are presented.
Observed decreases of PAD P1 and PAD P2 treatments began
between DOY 182 and DOY 185. After resuming irrigation of the
PAD treatment, leaf area expansion rate increased rapidly, but
the slope was less than that of the I treatment. The result
was irreversibly reduced leaf area of PAD plants.

Figure 1.12 delineates leaf growth.(measured.as the leaf
emerged from the whorl) for a single leaf growing before,
during, and after the PAD during 1989. Growth was plotted as
a function of thermal time to normalize the two planting
dates. These data indicated that duration of growth was
altered only slightly by the water deficit, whereas, growth
rate was reduced considerably more as evident by the expansion
rate of leaf 14 which was growing during the deficit. This
suggests that "windows of time" exist.for growth of individual
plant organs which are primarily a function of thermal time.
The delayed appearance of leaf 17 for PAD treatments depicted
in Figure 1.12 indicated that the reduction in expansion rate
for this leaf occurred while the blade was growing inside the
leaf sheathes or whorl of the plant.

Final leaf size during 1989 and final internode lengths
during'both.years are depicted in Figures 1.13a through 1.13c.

All leaves after leaf 10 for the PAD P2 treatment and leaf 11

—1
Accumulated Leaf Area (cm2 plant )

Figure 1.11.
hybrid 3540 during 1989.

39

 

 

 

 

9000‘ r .
800043-3869-le :. : ”I"
T];t HM)P2 : 1
7000-? : | W
6000? :- :
1 i i
. I
5000: :
. I
4000€ : :
j i 1
3000: : :
.. l I
.. I
20001 I :
" I
1000-1 / . i
j t 1 1
0‘ : 1
150'150 110 190 190 200 210 220 230 240

Day of Year

Leaf area accumu
The

lation for all treatments of
region between the vertical

dashed lines depicts the deficit period.

4O

 

o—oIP1
¢ H PAD P2

Lufl14

LaflIO

2)

 

 

Lufl17

 
 

\-.----—--

 

Leaf Area (cm

 

 

 

 

 

200 300 400 500 600 700 800 ' 900 r1000
. 0
Thermal lime After Plantlng ( Cd)

Figure 1.12. Growth of individual leaves for all treatments
of hybrid 3540 during 1989 before (leaf 10), during (leaf l4),
and after (leaf 17) the pre-anthesis deficit as a function of
thermal time after planting. The region between vertical
dashed lines represents the thermal time of the pre-anthesis
deficit of the second planting date, and the region between
the vertical solid lines represents the thermal time of the
pre-anthesis deficit of the first planting date.

41

 

 

 

 

 

A 1000
v— . o—e I|P1
"_ 900- a—a PAD P1
0 ‘ A—A PAD P2
.9 800-
N .
E 700-
0 d
V 600-
o .
8 500—
<( .
“5 400-
0 .,
—' 300-
E ..
:3 200-
E’ .
'§ 100-
O .
2 O 1'1'111'1r'1'1r1'
2 4 6 8 10 12 14 16 18 20 22
Node Number
Figure 1.13a. Maximum area of individual leaves for all

treatments of hybrid 3540 during 1989.

42

 

o—ol
o—aPAD

l L

l A

d
O
..l

 

Final lnternode Length (cm)
.3”. . ‘f‘

 

 

 

I fl I

I Ifr'I'l
246810121416

I r 1 I I
18 20 22
Node Number

Figure 1.13b. Final internode lengths for all treatments of
hybrid 3540 during 1988.

43

(A
C

 

.o—olP1
:o—aPADPl
A—APADPZ

N
U"
1

1o
‘1’

l A

a...
O
Alli

 

Final lnternode Length (cm)
‘7’“

 

 

 

I

11 I‘I‘T‘I I1Ir
2 4 6 8 10 12 14 16 18 20 22

Node Number

Figure 1.13c. Final internode lengths for all treatments of
hybrid 3540 during 1989.

44
for the PAD P1 treatment were smaller than the I P1 treatment
during 1989, although, the difference for the final leaf was
negligible. Internades above number 11 were not reduced by
the water deficits, and in fact some compensation growth was
apparent. ‘While the fact that.more leaves were growing during
the deficit period than internodes caused some of the
difference between these two plant components, there also may
be different and more flexible windows of time for internode
expansion than those of leaves.

Acevedo et a1. (1971) found that a mild deficit did not
influence final leaf size of corn, rather it simply postponed
growth. On the other hand, Jordan (1983) presented similar
results for sorghum leaves in response to a water deficit as
those observed in the current study for corn leaves. He also
reported a reduction in leaf number, suggesting that water
deficits before floral initiation. may reduce final leaf
numberu IRitchie and Hanway (1984) indicated floral initiation
occurs in corn around stage V5 (fifth leaf ligule present).
There was no difference in leaf numbers in the present study
probably because floral initiation was completed before the
PAD treatments were imposed.

The linear response of leaf appearance to temperature is
well documented in the absence of stress (Hesketh and
Warrington, 1989; Tollenaar et al., 1979: Warrington and
Kanemasu, 1983). Figures 1.14a through 1.14c portray leaf

tip appearance during both years and leaf ligule appearance

45

22 1
a I
20“ :1 PAD

 

I
I
I
I
O

O U D

o-------------
0

Leaf Tip Number
E3

 

 

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
L
I

O
.r-------——-

 

d
o I I I I I I I I f r I 1 I I

0 200 400 600 800 1000
Thermal Time After Planting (°Cd)

1200

Figure 1.14a. Leaf tip number for all treatments of hybrid
3540 during 1988 as a function of thermal time after planting.
The region. between ‘vertical dashed lines represents the
thermal time of the pre-anthesis deficit treatment.

46

 

 

 

 

 

 

 

22 r 1
201 a 1P1 : 1
. 2 :12; E i use“
18% 1 1 +0°%
‘ i 0: ° AADD
L- 16- .
4) 0° ' a
‘g 14.: 5 311.19?
3 . . age .
2 12~ 1 [if 1
I I
(1 1
- 10-1
1- . g: :
“a 8- Age :— :
3 5- 9‘0 l i
. .6 : :
4- m : :
‘ I I
29 g :
. 1 '
O I ' t—Iflr ' If? ' ' ' r '1 ' fl T U I I r r
0 200 400 600 800 1 000 1 200

Thermal Time After Planting (°Cd)

Figure 1.14b. Leaf tip number for all treatments of hybrid
3540 during 1989 as a function of thermal time after planting.
The region. between. vertical dashed lines represents the
thermal time for the pre-anthesis deficit of the second
planting date, and the region between vertical solid lines
represents the thermal time for the pre-anthesis deficit of
the first planting date.

47

 

1 o 1P1
20' a 91091

. 83°"
18" A PAD P2 -

 

3
1
--Q—--------d
90

“$0

 

Leaf Ligule Number
D

03
e I
D
ah

 

 

 

O I I I II I I j I I I I I I I I I

o 200 400 . 600 800 1000 11200
Thermal Time After Planting (°Cd)

J

 

 

1
d.----

Figure 1.14c. Leaf ligule number for all treatments of hybrid
3540 during 1989 as a function.of thermal time after planting.
The region Ibetween 'vertical dashed lines represents the
thermal time for the pre-anthesis deficit of the second
planting date, and the region between vertical solid lines

represents the thermal time for the pre-anthesis deficit of
the first planting date.

48

during 1989. A linear response to thermal time was observed
for all treatments until 500 to 550 °Cd. Treatments
experiencing water deficits began to deviate at this point,
which corresponded to the real time (see Figure 1.2) at which
extension growth began to decrease. After irrigation resumed,
leaf appearance returned to the same rate as it was prior to
the deficit. Leaf tip and ligule appearance responded
similarly to the shortage of water.

Measurement of individual leaf growth is time consuming
for a large number of plants. However, extension growth has
potential value in evaluating crop water needs, especially in
irrigation scheduling. An alternative to measuring whole leaf
growth was examined in this study. Figures 1.15a and 1.15b
portray dynamics of height to the top leaf ligule for all
treatments during 1988 and 1989. This measurement can.be made
rapidly on several plants. The time at which values for
deficit plants began to deviate from those of control plants
was similar to that found with leaf expansion measurements.
The relationship between height to the top leaf ligule and
accumulated leaf area is illustrated in Figure 1.16 for a
combination of planting dates, water regimes, and cultivars
from the 1989 experiment. While the absolute value of the
ligule measurement may be of little consequence, a
correlation with leaf growth and leaf area development was
possible. Also, as described previously, relative extension

growth was easily determined from the ligule heights.

49

 

240‘ 0—0 I'
220: H PAD

 

..A
.5
O

1

Height to Top Leaf Ligule (am)
$23
0
l

4 I

l
o TIII IITI'I'IIITI'T III I'IIIT'IFIIIIIIII IIII IIII

150 160 170 180190 200 210 220 230 240

 

 

 

Day of Year

Figure 1.15a. Height to the top leaf ligule for all
treatments of hybrid 3540 during 1988. The region between the
vertical dashed lines depicts the deficit period.

50

 

o—olPl
270 a—aPADPl
‘HPADPZ

__————---——————-—-1

      

  

Height to Top Leaf Ligule (cm)
£9
I I n

I
l
1
L

 

 

. "’ |
c 1
I I llTIII

Day of Year

Figure 1.15b. Height to the top leaf ligule for
treatments of hybrid 3540 during 1989. The region between

vertical dashed lines depicts the deficit period.

150 'iéo"iio"i§6"iéo"é66"21o 2&0"éio

 

240

all
the

‘ -1
Leaf Area (cm2 plant )

Figure 1.16.

51

 

4000-

3000- '

1

2000-

q

1000-

 

0

8

1‘

as
.f

V

+

ODDQX-I-

 

3475 PAD P
3475 PAD P
3475 1 P1
3540 PAD P
3540 PAD P
3540 1 P1

 

'TII‘ITI'I'I'I'I'ITI‘T'
0 20 40 60 80 100 120 140 160 180 200 220
Height to Tap Leaf Ligule (cm)

Plant leaf area as a function of height to top
leaf ligule for a combination of cultivars,
and water regimes during 1989.

planting dates,

52

In summary, results have indicated water absorption rate
in. the surface soil was strongly correlated. with. plant
extension growth. Reductions in extension growth caused by
soil water deficits resulted in small leaves and shortened
internodes as the effects were irreversible. Leaf appearance
was modified under deficit conditions from the generally
reported linear response to temperature. The use of height
to the top leaf ligule in evaluating plant extension growth
was effective and has advantages over the more tedious leaf

measurements.

LIST OF REFERENCES

Acevedo, E., E. Ferres, T.C. Hsiao, and D.W. Hendersona 1979.
Diurnal growth trends, water potential, and osmotic adjustment
of maize and sorghum leaves in the field. Plant Physiol. 64:
476-480.

Acevedo, E., T.C. Hsiao, and D.W; Henderson. 1971. Immediate
and subsequent growth responses of maize leaves to changes in
water status. Plant Physiol. 48: 631-636.

Barlow, E.W.R. 1986. Water relations of expanding leaves.
Aust. J. Plant Physiol. 13: 45-58.

Blackman, P.G. and. W.J. Davies. 1985. Root to shoot
communication in maize plants of the effects of soil drying.
J. Exp. Bot. 36 (162): 39-48.

Blum, A. and J.T. Ritchie. 1984. Effect of soil surface
water content on sorghum root distribution in the soil. Field
Crops Res. 8: 169-176.

Boyer, J.S. 1970. Leaf enlargement and metabolic rates in
corn, soybean, and sunflower at various leaf water potentials.
Plant Physiol. 46: 233-235.

Claassen, M.M. and R.H. Shaw. 1970. Water deficit effects
on corn. II. Grain components. Agron. J. 62: 652-655.

Davies, W.J., J. Metcalfe, T.A. Lodge, and A.R. da Costa.
1986. Plant growth substances and the regulation of growth
under drought. Aust. J. Plant Physiol. 13: 105-125.

Denmead, O.T. and R.H. Shaw. 1960. The effects of soil
moisture stress at different stages of growth on the
development and yield of corn. Agron. J. 52: 272-274.

Foale, M.A., R. Davis, D.R. Upchurch. 1986. The design of
rain shelters for field experimentation: A review. J. Agric.
Eng. Res. 34: 1-16.

53

54

Grant, R.F., B.S. Jackson, J.R. Kiniry, and G.F. Arkin. 1989.
Water deficit timing effects on yield components in maize.
Agron. J. 81: 61-65.

Gollan, T., J.B. Passioura, and R. Munns. 1986. Soil water
status affects the stomatal conductance of fully turgid wheat
and sunflower leaves. Aust. J. Plant Physiol. 13: 459-464.

Hesketh, J . D. and I .J . Warrington. 1989 . Corn growth
response to temperature: rate and duration of leaf emergence.
Agron. J. 81: 696-701.

Hoogenboom, G., M.G. Huck, and C.M. Peterson. 1987. Root
growth rate of soybean as affected by drought stress. Agron.
J. 79: 607-614.

Hsiao, T.C. 1973. Plant responses to water stress. Ann.
Rev. Plant Physiol. 24: 519-570.

Johnson, D.R. and.J.W. Tanner. 1972. Comparison of corn (Zea
mays L.) inbreds and hybrids grown at equal leaf area index,
light penetration, and population. Crop Sci. 12: 482-485.

Jordan, W.R. 1983. Whole plant response to water deficits:
An overview. In Taylor, Jordan, and Sinclair (ed.)
Limitations to efficient water use in crop production. pp.
289-317. ASA, CSSA, SSSA, Madison, WI.

Linvill, D.E., R.F. Dale, and H.F. Hodges. 1978. Solar
radiation. weighting for' weather' and. corn. growth. models.
Agron. J. 70: 257-263.

Ludlow, M.M. 1987. Defining shoot water status in the most
meaningful way to relate to physiological processes. In Hanks
and Brown (ed.) Measurement of soil and plant water status.
Proc. Inter. Conf., Logan, UT. 6 July - 10 July 1987. Utah
State University, Logan, UT, USA.

Martin, E.C., J.T. Ritchie, S.M. Reese, T.L. Loudon, and B.
Knezek. 1988. A large-area, light-weight rainshelter with

programmable control. Trans. Am. Soc. Agric. Eng. 31: 1440-
1444.

Meyer, W.S. and G.C. Green. 1980. Water use by wheat and

plant indicators of available soil water. Agron. J. 72: 253-
257.

Michelena, V.A. and J .S. Boyer. 1982. Complete turgor
maintenance at low water potentials in the elongating region
of maize leaves. Plant Physiol. 69:1145-1149.

55

NeSmith, D.S., A. Miller, and J.T. Ritchie. 1990. An
irrigation system for plots under a rain shelter. Agric.
Water Management (In press).

NeSmith, D.S., J.T. Ritchie, and A.J.M. Smucker. 1990. Pre-
anthesis soil water deficit effect on corn (gaa mays I").
III. Biomass and nitrogen accumulation and partitioning.
(companion paper).

Ritchie, S.W. and J.J. Hanway. 1984. How a corn plant
develops. Iowa State Univ. Coop. Ext. Ser. Spec. Rep. 48.

Robins, J.S. and C.E. Domingo. 1953. Some effects of severe
soil moisture deficits at specific growth stages in corn.

Rosenthal, W.D., G.F. Arkin, P.J. Shouse, and W.R. Jordan.
1987. ‘Water'deficit effects on transpiration and leaf growth.
Agron. J. 79: 1019-1026.

Schulze, E.D. 1986. Whole-plant responses to drought. Aust.
J. Plant Physiol. 13: 127-141.

Sharp, R.E. and W.J. Davies. 1979. Solute regulation and
growth by roots and shoots of water-stressed maize plants.
Planta 147: 43-49.

Taylor, H.M. and.B. Klepperx 1973. Rooting density and.water

extraction patterns for corn (Zaa mays L.). Agron. J. 65:
965-968.

Tollenaar, M., T. Daynard, and R. Hunter. 1979. Effect of
temperature on rate of leaf appearance and flowering date in
maize. Crop Sci. 19: 363-366.

Turner, N.C. 1986. Adaption to water deficits: A changing
perspective. Aust. J. Plant Physiol. 13: 175-190.

Upchurch, D.P., J.T. Ritchie, and M.A. Foale. 1983. Design

of a large dual-structure rainout shelter» .Agron. J. 75: 845-
848.

Warrington, I.J. and E.T. Kanemasu. 1983. Corn growth
response to temperature and photoperiod. II. Leaf initiation
and leaf-appearance rates. Agron. J. 75: 755-761.

CHAPTER 2

PRE-ANTHESIS SOIL WATER DEFICIT EFFECT ON CORN (ZEA M L.) .
II. REPRODUCTIVE GROWTH AND DEVELOPMENT

Water deficits during the flowering and pollination
period of determinate species such as corn are often
devastating to crop yields, however, those occurring prior to
anthesis generally have the greatest impact on leaf and stem
growth. An increased interest in irrigation water savings
through reduced applications contributes to the need for
further understanding of how intermittent water deficits
effect the whole crop. Research was conducted during 1988
and 1989 in Michigan utilizing a rain shelter to impose a pre-
anthesis soil water deficit on two corn hybrids under field
conditions to determine the immediate and subsequent responses
of the crop to the paucity of water. Planting dates and
hybrids provided a range in developmental patterns.
Treatments consisted of an irrigated control and an 18 to 21

day water deficit which was ended a week or more prior to

56

57
tassel emergence of control plants. Results demonstrated that
tassel and silk.emergence.as*well as beginning grain fill were
delayed 2 to 3 days for water deficient plants. Intact ear
size was reduced under deficit conditions, as were yields by
15 % to 25 %. Grain number was the component most responsible
for yield loss, however, examination of grain size
distribution revealed a higher percentage of seeds weighing
less than 100 mg were present on ears of water deficit plants.
The impact of the water shortages on vegetative growth and
development and on biomass and nitrogen accumulation and

partitioning are presented in companion papers.

lHIBQDQQIIQE

Water deficits during or shortly after anthesis are
considered to be among the most devastating to crop yields,
especially for determinate species such as corn (Begg and
Turner, 1976). The reduction in yield depends on the severity
and duration of the deficit (Robins and Domingo, 1953). The
primary component responsible for yield decreases during this
growth stage has been found to be grain number (Claassen and
Shaw, 1970b; Grant et al., 1989), and this has been
attributed, in part, to poor synchronization in emergence of
male and female flower components (Hall et al., 1982: Herrero

and Johnson, 1981).

58

Pre-anthesis water deficits have been shown to reduce
leaf growth substantially (Acevedo et al., 1971: Boyer, 1970:
Rosenthal et.al., 1987: Van Volkenburgh and Boyer, 1985). The
ensuing effects on reproduction and yield were not reported
for these experiments. Hall et al. (1981) found that a water
shortage just prior to tasseling reduced leaf area 13 96,
delayed silk emergence six days, and reduced yields 50 % as
compared to irrigated plants. Claassen and Shaw (1970a and
1970b) included a pre-anthesis deficit treatment in their
experiment and observed leaf dry weight decreases followed by
yield reductions of 12 96 to 15 96. Grant et al. (1989)
reported no yield loss due to a soil water deficit during
vegetative growth.

Water savings through reduced irrigation do not seem
feasible during the flowering period in corn, however, there
may be savings potential before anthesis. An increased
understanding of the impact of water shortages on plant growth
and yield during this growth stage is needed. An experiment
was conducted to examine immediate and subsequent effects of
corn growth and development in response to pre-anthesis soil
water deficits in a field environment. Results of
reproductive growth and development are reported here, while
results of vegetative growth and development, and of biomass
and nitrogen accumulation and partitioning are reported in

companion papers.

59

MAIEBIAL§_AHD_NEIEQD§

Corn.was grown in an area that could be covered by a rain
shelter at the Kellogg Biological Station near Kalamazoo, MI,
‘USA, during 1988 and 1989. There ‘were two irrigation
treatments, an irrigated control (I) and a pre-anthesis
deficit (PAD), and two cultivars, Pioneer hybrids 3540 and
3475, during both. years. Additionally, there were two
planting dates in 1989 (P1 and P2). Treatments and
experimental establishment were further described in a
companion paper (NeSmith et al., 1990). The deficit period
during 1988 was from day of year (DOY) 168 to DOY 189, and
during 1989 it was from DOY 175 to DOY 193.

Silking measurements were made on eight sample plants
per plot during 1988, and tasseling and silking measurements
were made on ten random plants per plot in 1989. Tasseling
was declared.when the tassel tip was clearly visible emerging
from the whorl of the plant, and silking was determined as the
day when there were any visible silks for a respective plant.
Recordings were made every two or three days, and percentages
of the population were calculated.

A compounded measurement of elongation of husks, shanks,
and ears (referred to as intact ear length) was determined for
eight and four sample plants per plot during the first and
second year, respectively. During 1988, a point of reference

was marked on a stem at the node just above where an ear was

60
attached to the plant. During 1989, the point of reference
was the node at which the respective ear'was attached” Length
was determined by recording the distance between the reference
point and the tip of the visible husk.

During 1989 single kernels were taken from two plants
per sub-plot twice weekly after grain filling began. Husks
were gently pulled back on sample ears, and five individual
kernels were removed from the center portion using a small
knife and were placed in an envelope. After oven drying at
60 °C, weight was determined for each grain individually.
After each sampling, ears were covered by the husks which were
then held in place with a rubber band. The same plants were
used for all the sampling dates.

Single ears were harvested both years from which yield,
grain numbers, and final grain weight were determined. on
19 September 1988, four plants were harvested in each plot,
and on 27 September 1989, twenty plants were harvested. Ears
were placed in an oven at 60 °C for four days. After drying,
grain was removed from each ear manually and was weighed and
counted. During 1989, grain size distribution was determined
for a sub-sample of ears. This was accomplished by weighing
individual kernels of an 80 cm3 (ca. 200 kernels) sample from
single ears. These kernels were categorized in 50 mg

increments for three ears of each plot.

61

BE§QLI§_AHD_DI§QH§§IQE

Results of a companion paper (cited previously)
describing vegetative growth and water absorption rates
demonstrated that leaf extension rate was reduced in response
to the PAD treatments, resulting in decreased leaf area and
delayed emergence of leaves from the whorl of the plant that
continued after irrigation resumed. The influence of the
deficit was not on leaves only, however. Figures 2.1a and
2.1b depict tasseling for Pioneer hybrids 3540 and 3475 during
1989, and Figures 2.2a through 2.2c portray silking for the
hybrids during both years. Pioneer 3475 flowered about two
days before 3540, and this was attributable to a developmental
difference of one leaf between the hybrids. There was,a delay
in appearance of tassels and silks of PAD plants during both
years. The two hybrids were affected similarly, with
generally a three to four day difference between the I‘and RAD
treatments. The second planting date during 1989 provided a
more extensive range of flowering dates. It was hypothesized
that plants further away from the time of flowering when the
PAD‘was imposed would be affected less by the treatment" This
was not the result, however, as tassel and silk appearance of
plants from the PAD P2 treatments were delayed similar to the
PAD P1 treatment. There was a trend for PAD plants in general
to take longer to reach 100 % tasseling once it began,

indicating an increased variation among stressed plants.

62

 

100 o—o 3540 I P1
‘ H 3540 PAD P1
90" H 3540 PAD P2

   

Tasseling Percentage

 

 

 

 

0 TUrUIU' "j TIFT'U‘FU IIUV

190 195 200 205 210 215 220
Day of Year

Figure 2.1a. Tasseling percentage of treatments as a function
of time for hybrid 3540 during 1989.

63

 

100- 0—0 3475 I P1
‘ H 3475 PAD P1
90" H 3475 PAD P2

804

Tasseling Percentage

 

 

 

 

 

C
O I I U j I I I ' I 1 I ‘ T I I V

190 195 200 ~ 205 ': 210 215 220
Day of Year

Figure 2.11:. Tasseling percentage of treatments as a function
of time for hybrid 3475 during 1989.

64

 

100 0-0 3540 Irrigated
' s—a JSflJPMD

90" H 3475 Irrigat-o
80; v—v 3475 PAD ‘

Silking Percentage

  

 

   
  
 

 

 

o rivrTfir ‘II'IIIIIIIU

_. . I
190 195 200 205 210 21

   

Day of Year

'UUIIFU'

5 220

VIT'UI

225

 

230

Figure 2.2a. Silking percentage of treatments as a function

of time for both hybrids during 1988

65

 

 
 
  

100 o—o 3540 I P1
‘ s—a 3540 PAD P1
90‘ H 3540 PAD P2
0 80"
.c» .
3 70-
g 4’
o 60‘
L. .
33 50-
c» 1
.5 4°“.
éé 130-
U) .
20-
19-
‘o . . . . . ,

 

 

 

 

I - ' -~ , -- 1 I I U I ’ I
190 155 200 205 210 215 220
Day of Year

Figure 2.2b. Silking percentage of treatments as a function
of time for hybrid 3540 during 1989.

66

 

100- e—a 3475 1 P1
‘ ai—a 3475 PAD P1
90: H 3475 PAD P2

Silking Percentage

 

 

 

 

 

l
OIIIWIVT-fitf1fim*tvtirivit

190 195 200 205 210 215 _ 220
Day of Year

Figure 2.2c. Silking percentage of treatments as a function
of time for hybrid 3475 during 1989.

67

Tassel and silk emergence were delayed for deficit plants
in the current study even though irrigation had resumed.a‘week
or more before tassel emergence of control plants. Other
researchers have reported delayed silk emergence of one to
eight days as a result of a water deficit during, or a few
days prior to, anthesis (Grant et al., 1989: Herrero and
Johnson, 1981; Hall et al., 1981; Robins and Domingo, 1953;
Vincent and Woolley, 1972). Unpublished data of the current
authors have shown that tassel and silk emergence can be
delayed as much as fourteen days on a sandy soil by such
deficits. Poor synchronization in emergence of male and
female reproductive components occurred in several of the
aforementioned experiments. This was not observed in the
current study, as therewwas generally the same time separation
between tasseling and silking of PAD plants and I plants.

Figures 2.3a through 2.3a delineate intact ear length
for treatments during 1988 and 1989. There was a postponed
appearance of ears for PAD plants which was proportional to
delays previously described for leaves, tassels, and silks.
Ritchie and Hanway (1984) indicated.that ear shoots are formed
around stage V5 (fifth ligule visible). The deficits of the
current study occurred well after this growth stage and should
not have influenced ear initiation. The smaller ears of PAD
plants were a result of reduced growth rate rather than a

shortened duration of growth. According to Ritchie and

68

 

  
        

 

 

25
0—0 3540 Irrigated
:s—a 354D PAD
A . H 3475 Irrigated
E 201 H 3475 PAD
U 1
v
{5 .
c» 15-
C J
a) .
—J .
a 4
Lu ~10?
H .
o .
£3 .
s. 5-
O UIjVITU' 'i‘l UUFV1TY'I1III1

 

 

190 195 200 ' 2D5 250 215 220 225 230
Day of Year

Figure 2.3a.

Intact ear length of treatments for both hybrids
during 1988.

69

 

8

9—0 3540 I P1
s—a 3540 PAD P1
H 3540 PAD P2

61
S"

(:4
<3
.1.

N
‘f‘

llLLll

d
U‘
I

I

Alli

Intact Ear Length (cm)
215 B

1-1

01

Llll‘ll

I
I
I
I
I
I
I
I
I
I

'.

 

o .

 

 

 

 

UIU'T—UVTT' TYFU 'YrUlIV'I 1'11

190 195 200 205 2io 215 220 225 230
Day of Year

Figure 2.3b. Intact ear length of treatments for hybrid 3540
during. 1989. The dashed line represents the probable
beginning date of ear appearance:for the respective treatment.

70

 

40 ‘
1 0—0 3475' P1
35; s—a 3475 PAD P1
A 1H3475PADP2
Esme
‘~/ .
£3 25$
0‘ I
C: . h
.23 201
E; I
m15—j .
+4 j ”
C) . r
C) 10- I
J-I ‘ 1
CI 1 I
__ ‘ '
51 ;
‘ r
j I
O U‘Ir IIYWI VjUIlYTTTIIU‘T‘rI‘TU

 

 

 

 

190 195 200 205 210 215 220 225 230
. Day of Year

Figure 2.3c. Intact ear length of treatments for hybrid 3475
during 1989. The dashed line represents the probable
beginning date of ear appearance for the respective treatment.

71

Hanway (1984) water and nutrient deficiencies at growth stage
V12 (twelfth ligule visible) can result in reduced ear size.
Figures 2.4a and 2.4b portray single grain weight for
all treatments of the current experiment during 1989. There
was a delay in beginning grain filling of three to four days
for PAD plants which was similar to postponements in other
developmental events such as leaf appearance and flowering.
The linear phase of grain filling tended to end at the same
time regardless of treatment, resulting in a slightly
shortened grain filling period for the PAD plants. There was
no apparent influence on the rate of grain filling for hybrid
3475 due to the PAD, however, there was an observed increase
in the rate for hybrid 3540. Several investigators have
studied the influence of a variety of post-flowering stresses
on grain filling (Barnett and Pearce, 1983: Frey, 1981; Jones
and Simmons, 1983; Tollenaar and Daynard, 1978), but the
impact of stress prior to flowering on subsequent grain
filling has not been as widely reportedr Lorens et al. (1987)
observed a seed growth rate decrease of 7 % for one hybrid and
an increase of 2 % for another in response to a vegetative
water deficit. They also calculated slight differences in
effective grain filling period in response to the paucity of

water.
Reported yield decreases due to pre-anthesis water
shortages range from no reduction to over 70 % loss (Claassen

and Shaw, 1970b; Grant et al., 1989; Hall et al., 1981;

72

350

 

1 0—0 3540 I P1
1 s—a 3540 PAD P1
. H 3540 PAD P2

—1
)
u
o
‘1’

N
U‘
‘?

llLl

Grain Weight (mg seed
‘5:
C
l

50-:

 

 

 

C
o TIT‘IUUFY—IT‘I

YUWII‘ITU1FUYIIfYUT

210 220 230 ‘2}.0' 250 260 270 280
Day of Year

Figure 2.4a. Grain filling as measured by single kernel
samples for treatments of hybrid 3540 during 1989.

73

 

 

 

 

350
: H 3475 1 P1
A : s—a 3475 PAD P1 .
T 300‘. H 3475 PAD P2 .- 31g
8 1”
0 250:_ 1 :91“
(D «1
a] a:
E 200-;
V .
43 I
.c 150-
.9 i
Q) .
3 10.0-
.E 3
E I
o 50:
0 YVFUITTUT'V'UU VUTII UYTIU'UYIT"

 

1 1
21 0 220 230 240 250 260 270 280
Day of Year

Figure 2.4b. Grain filling as measured by single kernel
samples for treatments of hybrid 3475 during 1989.

 

74

Lorens et al., 1987). This variation is attributable to
differences in deficit severity and timing in the various
experiments. Results of the current study generally showed
a yield reduction of 15 % to 25 95 in response to PAD
treatments for hybrids and years overall (Figures 2.5a through
2.5c). The component most responsible for yield decrease was
grain number. This agreed with findings of Claassen and Shaw
(1970b), Hall et al. (1981), and Lorens et a1. (1987).

Grant et al. (1989) observed no influence of pre-anthesis
water deficits on grain number and indicated the interval of
sensitivity to this yield component began some time after
silking. Kiniry and Ritchie (1985) concluded that such a
post-silking interval was the time when grain number was most
responsive to stresses, however, their data revealed that
reductions could be caused as early as thirty days prior to
flowering depending on the hybrid. Sadras et al. (1985)
constructed a model in which kernel set was not affected by
stress if it was relieved five days or' more prior to
pollination. The data from 1989 of the current study did not
indicate largest reductions in.grain.number for’plants nearest
flowering when deficits were imposed, instead the opposite was
found. Grain numbers were 12 %, 14 %, 14 %, and 18 % less
than control plants for 3475 PAD P1, 3540 PAD P1, 3475 PAD P2,
and 3540 PAD P2 treatments, respectively.

Reduction in grain weight caused by PAD treatments was

observed, but there were varying responses. Hybrid 3475

75

  
  
 
 
   

300
12335401
ans 122134751
"|" T 250 EMPAD
$533475PAD
'8 ‘5 225
83200
0’ (11175
E E
...: v
€; 12 125
g 3100
.S .5

   

Yield Grain Wt. Grain No.

Figure 2.5a. Grain yields, final grain weight,
number for treatments of both hybrids during 1988.

0| 0| (3 0'
CDC 0 O

N
8
Grain Number per Ear

and grain

76

300 3540 1 P1
1::

275 a 3540 PAD P1

250 1:53 3540 PAD P2

225
200
- 175
1 50
1 25
100
75
50
25

Grain Weight (mg seed
Grain Yield (gms plant

 

Yield Grain Wt.

Figure 2.5b. Grain yields, final grain weight,
number for treatments of hybrid 3540 during 1989.

 

Grain No.

600
550
500
450
400
350
300
250
200
1 50
1 00
50

  

and grain

Grain Number per Ear

77

 

 

  

300 600
2 C3 3475 I P1 550
A E 3475 PAD P1
.- .." 250 1:53 3475 PAD P2 500
I
'3 I‘é’ 225 450
8 ~31 200 400
CE” 111 175 . 350
V g 150 30°
41-0
'5, '2 125 250
'5 3 100 200
3 )- 150
.E .E
E g 100
0 50
0 Yield Groin Wt. Grain Na.
Figure 2.5c. Grain yields, final grain weight, and grain

number for treatments of hybrid 3475 during 1989.

Grain Number per Ear

78

appeared more sensitive to reductions in this yield component
than hybrid 3540. Generally, grain weight is determined by
weighing a large sample of seed and then dividing by the
numberu This assumes an equal distribution of seed size among
treatments. Figures 2.6a through 2.6f demonstrate dissimilar
seed.size1distributions occurred among treatments.during 1989.
PAD plants had a greater proportion of seeds under 100 mg than
I plants. If seeds weighing less than 100 mg were discarded,
distributions and average grain weight were the same for
treatments. These small seeds added little to the total ear
weight and would probably not have been.retained.in mechanical
harvesting.

Claassen and Shaw (1970b) demonstrated that grain weight
was reduced.during'a‘vegetative'water'deficit when all kernels
were considered. However, when they adjusted for small, less
developed seeds they calculated no difference in weight. The
criteria they used for classifying seeds was diameter. Seed
diameter can be useful, but the variation in shape of kernels
among hybrids may pose problems“ Separating seeds on.a‘weight
basis in the current investigation was laborious, however,
this method was determined to be less biased. Furthermore,
weight is generally considered when modeling grain growth.

The data from this experiment and that of Claassen and
Shaw (1970b) indicate that a threshold seed size needs to be
developed for determining effective yield components. This

lack of a standard may be a source of variability among

79

50

 

45.. 3540 1 P1

 

35-

30-

25- A 'l/

2, / 1-
15—

 

10-1

/ 7
5d 7/127/2 Wm, mm %% %///1%///1 maxi/1.

0"o 50 100 150 200 250 - 300 350 400

-1
Grain Size Class (mg seed )

 

Percentage of Grains per Ear

 

 

Figure 2.6a. Grain size distribution of single ears at
harvest for the hybrid 3540 I Pl treatment during 1989.

 

    

 
      
   

 

 
    

it; 20: %%

 
  

   

 

O 50 100 150 200 250 300 350 400 -

Grain Size Class (mg seed-1)

 

 

81

 

0'
O

- 3540 PAD P2

M3

'/,’//
¢

/%
. 7 l, I //
2 0027/1. 71% %%//A%///I%//2 Ill/III.

100 150 200 250 300 350 400
. . -1
Gram Slze Class (mg seed )

(A
O

....- 4—0
O m
l l I

 

Percentage of Grams per Ear
N N
O 01

 

W

 

Figure 2.6c. Grain size distributio '
. n of Single ears at
harvest for the hybrid 3540 PAD P2 treatment during 1989.

82

U1
0

 

3475 I P1

U-F-h
91??

%%
’/////.,,.....,,. Wfl%%/fl///A% WM

0 50 100 150 200 250 300 350 400
1

dNNU
9°C.”?
ll

 

Percentage of Grains per Ear
'15

U"
l

 

 

 

D

-1
Grain Size Class (mg seed )

Figure 2.6d. Grain size distribution of single ears at
harvest for the hybrid 3475 I P1 treatment during 1989.

U!
D

83

 

rEar

(at-#45

8880190.
[1111]

—o
0‘
l

10

 

Percentage of Grains pe

Figure 2 . 6e .

Z

100 150 200 250 300 350

3475 PAD P1

 

'7

1
i
l

‘A A

-1
Grain Size Class (mg seed )

V22

 

 

27272

400

Grain size distribution of single ears at
harvest for the hybrid 3475 PAD Pl treatment during 1989.

84

 

.0 —b N N (A U
D U. 0 U! C 01
I l l l l l

 

Percentage of Grains per Ear

5
0

Figure 2 . 6f .

100 150 200 250 300 350 400

3475 PAD P2

7/

 

27

/.

'///"

1

Grain Size Class (mg seed- )

Grain size

distribution of a s
harvest for the hybrid 3475 PAD P2 treatment during 1989.

single e

 

 

85
research reports which differ in the yield component most
sensitive to stresses. If all kernels are regarded weight
may be biased, and if certain ones are discarded grain number
may not be represented accurately. These factors need to be
considered when developing crop models that reliably predict
yield components.

In summary, results have shown that tassel emergence,
silk emergence, and beginning grain fill were delayed by pre-
anthesis water deficits even though irrigation resumed at
least a week prior to flowering of control plants. There was
no apparent synchronization problems between tassels and
silks. Intact ear size was reduced due to the water
shortages. Yields of deficit plants were 15 % to 25 % less
than irrigated plants. Grain number was the yield component
most reduced when mechanically harvestable seeds were
considered, although, examination of grain size distributions
revealed a higher percentage of seeds less than 100 mg were

present on ears of water deficient plants.

LIST OF REFERENCES

Acevedo, E., T.C. Hsiao, and D.W. Hendersona 1971. Immediate
and subsequent growth responses of maize leaves to changes in
water status. Plant Physiol. 48: 631-636.

Barnett, R.H. and R.B. Pearce. 1983. Source-sink ratio
alteration and its effect on physiological parameters in
maize. Crop Sci. 23: 294-299.

Begg, J.B. and N.C. Turner. 1976. Crop water deficits. Adv.
Agron. 28: 161-217.

Boyer, J.S. 1970. Leaf enlargement and metabolic rates in
corn, soybean, and sunflower at various leaf water“potentials.
Plant Physiol. 46: 233-235.

Claassen, M.M. and R.H. Shaw. 1970a. Water deficit effects
on corn. I. Vegetative components. Agron J. 62: 649-652.

Claassen, M.M. and R.H. Shaw. 1970b. Water deficit effects
on corn. II. Grain components. Agron J. 62: 652-655.

Frey, N.M. 1981. Dry matter accumulation in kernels of
maize. Crop Sci. 21: 118-122.

Grant, R.F., B.S. Jackson, J.R. Kiniry, and G.F. Arkin. 1989.
Water deficit timing effects on yield components in maize.
Agron J. 81: 61-65.

Hall, A.J., J.H. Lemcoff, and N. Trapani. 1981. Water stress
before and during flowering in maize and its effects on yield,
its components, and their determinants. Maydica XXVI: 19-38.

Hall, A.J., F. Vilella, N. Trapani, and C. Chimenti. 1982.
The effects of water stress and genotype on the dynamics of

pollen-shedding and silking in maize. Field Crops Res. 5:
349-363.

Herrera, M.P. and R.R. Johnson. 1981. Drought stress and

its effects on maize reproduction systems. Crop Sci. 21: 105-
110.

86

 

 

87

Jones, R.J. and S.R. Simmons. 1983. Effect of altered
source-sink ratio on growth of maize kernels. Crop Sci. 23:
129-134.

Kiniry, J.R. and. J.T. Ritchie. 1985. Shade-sensitive
interval of kernel number of maize. Agron J. 77: 711-715.

Lorens, G.F., J.M. Bennett, and L.B. Loggale. 1987.
Differences in drought resistance between two corn hybrids.

II. Component analysis and growth rates. Agron J. 79: 808-
(813.

NeSmith, D.S., J.T. Ritchie, and A.J.M. Smucker. 1990. Pre-
anthesis soil water deficit effect on corn (Zea mays L.). I.
Vegetative growth and development. (companion paper).

Ritchie, S.W. and J.J. Hanway. 1984. How a corn plant
develops. Iowa State Univ. Coop. Ext. Ser. Spec. Rep. 48.

Robins, J.S. and C.E. Domingo. 1953. Some effects of severe
soil moisture deficits at specific growth stages in corn.
Agron. J. 45: 618-621.

Rosenthal, W.D., G.F. Arkin, P.J. Shouse, and W.R. Jordan.
1987. ‘Water deficit effects on transpiration.and leaf growth.
Agron. J. 79: 1019-1026.

Sadras, V.0., A.J. Hall, and T.M. Schlichter. 1985. Kernel
set of the uppermost ear in maize: I. Quantification of some
aspects of floral biology. Maydica XXX: 37-47.

Tollenaar, M. and T.B. Daynard. 1978. Effect of defoliation

on kernel development in maize. Can. J. Plant Sci. 58: 207-
212.

Van‘Volkenburgh, E. and J.S. Boyer. 1985. Inhibitory effects

of water deficit on maize leaf elongation, Plant Physiol. 77:
190-194.

Vincent, G.B. and D.G. Woolley. 1972. Effect of moisture
stress at different stages on growth: II. Cytoplasmic male-
sterile corn. Agron. J. 64: 599-602.

 

 

CHAPTER 3

PRE-ANTHESIS SOIL WATER DEFICIT EFFECT ON CORN (ZEA MAYS L.).
III. BIOMASS AND NITROGEN ACCUMULATION AND PARTITIONING

Aw

Biomass accumulation and nitrogen uptake patterns in corn
are similar. Usually 65 % to 70 % of the total season
nitrogen is taken up by the mid-silking growth stage, hence,
interruption or alteration of pre-anthesis nitrogen
acquisition is potentially detrimental to dry matter
production and yield. Research was conducted during 1988 and
1989 in Michigan utilizing a rain shelter to impose an
intermittent water deficit on corn in a field environment
prior to anthesis. Biomass accumulation and partitioning
results indicated an 18 to 21 day water deficit during
vegetative growth reduced above ground dry matter production
of deficit plants 35 9s to 45 % as compared to irrigated
control plants. The greatest reduction was at the end of the
deficit period which was a week or more prior to tassel

emergence of control plants. Examination of crop growth rate

88

89
revealed there was a reduction for water deficit plants as
great as 65 %. Reduced leaf area as well as leaf rolling was
the major causal factor of the crop growth rate differences,
although, increased partitioning to roots of deficit plants
was observed as well. There were proportional reductions in
drwaeight of all above ground plant organs of deficit.plants.
Assessment of above ground nitrogen status 10 to 12 days past
silking revealed little difference in the percentage of this
element among treatments, although, absolute uptake was less.
Subsequent evaluation of grain nitrogen revealed similar
results. Results of vegetative and reproductive growth and

development are presented in companion papers.

OD N

Plant nitrogen status is important agronomically and has
-received considerable attention among experimenters. Hanson
and Hitz (1983) divided nitrogen economy into two phases, the
acquisition. phase and. the reallocation. phase, with some
overlap between phases. They indicated the acquisition phase
was nearly completed for cats shortly after anthesis.
Researchers have shown that 50 % to 90 % of corn's total
nitrogen was acquired by flowering, with most reports
indicating it was in the range of 70 % (Friedrich et al.,
1979; Hanway, 1962b: Karlen et al., 1987; Tsai et al., 1984:

Wolfe et al., 1988). Hanway (1962b) found that. grain

90

contained 65 % of the total nitrogen at harvest, and that this
was equal to the amount of nitrogen taken up at silking. In
an experiment with n N, Friedrich and Schrader (1979)
concluded that almost the entire amount of grain nitrogen was
that. acquired. prior' to silking. 131 fact, post silking
nitrogen deprivation did not reduce grain nitrogen content
even though the capacity for uptake still existed.

Interruption or alteration of pre-anthesis nitrogen
uptake can decrease biomass and grain yield significantly
because dry matter production and nitrogen uptake patterns
are similar (Hanway, 1962a and 1962b: Hanway and Russell,
1969). Verasan and Phillips (1978) reported plant dry weight
and nutrient accumulation were highly correlated with
evapotranspiration. Similar responses have been observed for
plants deprived of either water or nitrogen, which include
delayed flowering and reductions in leafWextension, leaf area,
biomass production, and. yield (Claassen and Shaw, 1970:
Denmead and Shaw, 1960: Greenwood, 1976: Hall et al., 1981;
Hanway, 1962a: Lorens et al., 1987: Radin and Boyer, 1982:
Wolfe et al.,1988). Kevlen (1981) discussed research innwhich
plant growth reductions seemingly caused by water shortage
were corrected by nitrogen applications deeper in the soil,
indicating that surface drying had reduced nitrogen uptake.
Rhoads (1984) reviewed.some interactions of‘water and nitrogen
stresses and suggested that water deficits reduce nitrogen use

efficiency.

91

The objective of this research was to utilize a rain
shelter to impose a soil water deficit prior to anthesis to
determine immediate and subsequent effects on corn growth and
development under field conditions. Vegetative and
reproductive growth and development responses have been
presented by the current authors in companion papers. Results
of biomass production, growth analysis, leaf area index, root

growth, and plant nitrogen status are presented here.

MAIEBIAL§_AND_MEIHQD§

Corn was grown in an area that could be covered by a rain
shelter at the Kellogg Biological Station near Kalamazoo, MI,
USA, during 1988 and 1989. There ‘were two irrigation
treatments, an irrigated control (I) and a pre-anthesis
deficit (PAD), and two cultivars, Pioneer hybrids 3540 and
3475, during both.years. Planting date in 1988 was 5 May (DOY
126). In 1989, there were two planting dates referred to as
P1 and P2, which were 3 May (DOY 123) and 17 May (DOY 137),
respectively. Plants were thinned. to a population of 7.9
plants mq‘at the fourth leaf stage. Row spacing was 0.71 m.
The deficit period was from DOY 168 to DOY 189 and from DOY
175 to D0! 193 during 1988 and 1989, respectively; .Additional
description of treatments and experimental establishment was

in a companion paper (NeSmith et al., 1990a).

92
Biomass for the above ground portion of the plants was
determined several times during the growing season each year
by a combination of nondestructive estimates and destructive
sampling. Biomass (BIOM) for 1988 was estimated from height
to the top leaf ligule (LIG) for the period from DOY 168 to
D0! 200 using the following equation which was fitted from

sampling in 1989:

BIOM = 16.2 + 0.46(LIG); r2 = .84 [1]

(30 cm < LIG < 160 cm)

After DOY 200, biomass was determined by harvesting four
plants per treatment and oven drying them at 60 °C until no
further weight loss occurred.

During 1989, leaf and stem biomass (LFBIOM and STMBIOM)
were estimated from plant leaf area (PLA) and height to the
top leaf ligule (LIG) for the period from DOY 166 to DOY 187

using the following equations fitted from sampling in 1989:

LFBIOM = 6.15 x 10‘3(PLA) - 2.83; r2 = 0.94 [2]

(2000 cm2 plant‘1 < PLA < 7000 cm2 plant'l)

STMBIOM = 3.02 x 10'1(LIG) + 0.89; r2 = 0.87 [3]

(30 cm < LIG < 160 cm)

93

Leaf biomass was for visible blades and sheathes only. The
stem biomass included leaves which had not emerged from the
whorl of the plant, as well as internodes. Beginning DOY 195,
biomass was obtained by harvesting four plants per treatment
and oven drying as in 1988. Individual plants were separated
into leaves (including sheath), stems (including tassel),
husks-silks-cobs, and grain on each sampling date the second
year.

Additionally for 1989, crop growth rate (CGR) was
calculated from the derivative of smooth fitted lines to
biomass data (see Brown, 1984: Radford, 1967), and leaf area
index (LAI) was estimated from leaf length, width, and
senescence measurements (see Johnson and Tanner, 1972; Linvill
et al., 1978). Net assimilation rate (NAR) was computed by
dividing CGR by LAI on a given day. CGR, LAT, and NAR were
calculated on a land area basis. Leaf rolling was assessed
between 1100 h and 1200 h on DOY 186 through DOY 188. These‘
were clear days with little or no wind. Measurements were
made on leaves 10, 11, and 12. The rolled width was measured
first, followed by the fully open width.

During 1988, root observations were made using a
minirhizotron system similar to that described by Upchurch
and Ritchie (1984), with modifications as described by
Ferguson and Smucker (1989) . There were six observation tubes
installed in each plot at a 45° angle. Root images were

recorded with a VHS video recording system to a vertical depth

94

of 1 m on three dates occurring before, during, and after the
water deficit period. Root observations were averaged for
each 0.1 m vertical depth increment.

During 1989, nitrogen content of plants sampled on 31
July (DOY 212) was determined by micro-Kjeldahl procedures
for leaves, stems, and ears. There was no appreciable grain
on this date, so the whole ear (husks, cob, silks) was
aggregated as a single sample. ZNitrogen content of grain only
was determined for DOY 227, DOY 249, and harvest (DOY 270)

plant samples.

D S 8 ON

There were no appreciable differences between hybrids in
the data presented here, and the averaging of them did not
influence statistical significance. Therefore, results for
hybrid 3540 only are discussed. Figures 3.1a and 3.1b depict
above ground biomass for treatments during 1988 and 1989, and
Figures 3.2a and 3.2b show solar radiation for the first and
second. year, respectivelyu The accumulation curves for
irrigated plants was similar to typical curves as described
by Hanway (1962a). The PAD plants deviated from this pattern
during the deficit period and never recovered fully after
irrigation had resumed. Maximum biomass reduction of PAD
plants as compared to ijlants during 1988 occurred at the end

of the deficit period, and it was 35 %. At harvest PAD

95

 

 

 

 

A
T 330 . I

"E 3001 ° H :

2 1 ° ”9 i

a 2701 i 1

g 240‘ : :

" 1 l .....

3 210: : : b
(0 : : : 0”, O

8 180: E i ’1’ ’IO’ ..... u
S 150-3 : :

.- ‘ 1 1 I I

P 120- : : x ,D

U j i l I, I”

g 90': i i o”

0 j I I I I

L 60" : :I’ 1’

0 : ' ’orI’IB

0)) 30-: 'u’ég’v’dr

0 1 1 J

n OIIIIrrrrU—Itltrllrtrlvir I
< 1 50 1 70 90 210 230 250 270

Day of Year

Figure 3.1a. Above ground biomass for treatments during
1988. The region between the vertical dashed lines depicts
the deficit period.

 

96

 

 

 

A
'1' 33° ,, 1 :

... 0 I .

g 300% a pm 911 : i

'5 270$ ‘ PAD“? : """ 4,
m 1 : : [I

g 240- . . ,z i ......
as I ' ' I ,2’

v 210.. : 3 ’¥ 2’ x} ......

. ' 2
8 180': : : I” I I’
(E) : | I I, ”1‘
150‘ I I ’ I, ’

..o. : : : I” I C?

CD 120: : i I, ",/I

2 90-3 i l f

3 J 1 19’ ," ’5

g 50.“ : exit/”I

a 30-5 if’ég”?

3 0- at. 1

D " T I I I I I I 1 I I I I I I I l 1 I I
< 150 170 1 90 21 0 230 250 270

Day of Year

Figure 3.1b. Above ground biomass for treatments during

1989. The region between the vertical dashed lines depicts
the deficit period.

 

97

 

 

 

 

 

 

 

 

 

40.
‘,\
I
>‘ 35 1988
(J
13
(r 30
ES 25%
-a i
.55 20{ l
s 1 '
:3 ‘5‘.
.9 :
'E3 10{
0‘ :
.5. 5%
<> :
01 0.
. . . ,. .. . .1 . A, . .. . ..

 

 

 

. .. , , ,. ..
120 110 150 180 200 220 240 260 280
Day of Year

Figure 3.2a. Daily solar radiation at the research site
during 1988.

98

 

I 35 1989

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

an.
01 0
¢
‘:
c:

 

Solar Radiation (Md m
a;

 

 

orYV'Ifi'T IYTTVT Trj‘UrU'TWU

. I. .,
120 140 1&0 180 260 220 240 250 280
Day of Year

Figure 3.2b. Daily solar radiation at the research site
during 1989.

99

biomass was 20 % less than I plants. During 1989, maximum
biomass reduction as compared to the I P1 treatment was again
at the end of the deficit period and was 32 % and 45 % for the
PAD P1 and PAD P2 treatments, respectively. At harvest PAD
P1 plants had 14 % less biomass than I P1 plants, and PAD P2
plants had 25 96 less. These results were in the range of
reductions found by other experimenters in response to pre-
anthesis water deficits.

Claassen and Shaw (1970) reported 15 % to 17 % less dry
matter at harvest caused by water deficits during vegetative
growth, and Lorens et al. (1987) observed 25 % to 30 % less.
Results of Grant et al. (1989) and, Hall et al. (1981)
indicated 12 % and 38 % biomass reductions, respectively, at
harvest. Wolfe et al. (1988) found a 40 % reduction in total
biomass on a two year average for nonirrigated corn as
compared to irrigated. Their results also showed a similar
biomass reduction for plants which received irrigation but no
nitrogen.

Figures 3.3a through 3.3d portray the distribution of
biomass to the various above ground portions of the plant
during 1989. There was a trend at the end of the deficit
period for stem weight to be reduced more than leaf weight for
PAD plants of both planting dates. Reductions at harvest,
however, were proportional for the different components,
indicating no significant influence of the PAD treatments on

above ground biomass partitioning. Stem weight and

100

 

e—e lPl'
135- s—a PAD P'l
j e—e HM)F9

50L Leaves

..--————-—-—-———------—-1

   
  

Biomass (gms plant—

 

 

 

I I I T W U 1 1’le I

150 170 190 210 230 250 270
Day of Year

Figure 3.3a. Leaf biomass for treatments during 1989. The
weight includes sheathes. The region between the vertical
dashed lines depicts the deficit period.

 

101

 

] G-O IPI '
13510—0 PAD P.1
. H PADPZ

60- Stem

I ‘\

   

Biomass (gms plant—

 

 

 

I
I
I
I
I
I
I
I
I
I
I
I
l
I
I
I
I
I
I
I
I
I
I
I
/
l
t

0 I I r r U—T T I D 1 r ‘ I I f1 I I I I r

150 170 t1§0 210 230 250 270
Day of Year

Figure 3.3b. Stem biomass for treatments during 1989. The
weight includes the tassel. The region between the vertical
dashed lines depicts the deficit period.

102

 

:o-alPi'
135:3—aPADP'1
J a—a HMDFQ

50: Husk +
3 Silk +
45: Cob

Biomass (gms plant— 1)

  

--...---------------------—-----4

q—------——--’------

 

 

 

  

 

q
0 frl ITT1UV—UTUUr

150 150 mic 210 230 250 2io'
Day of Year

Figure 3.3a. Husk, silk, and cab biomass for treatments
during 1989. The region between the vertical dashed lines
depicts the deficit period.

103

150

 

jo-alPi'
1351HPADF11
a—e BM)PQ

A

1

—b —l
:3 no
Ln :3
41 I

\I (D
"‘ ‘3
l l l A

50-: Grain

 

Biomass (gms plant—

'_
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
1

 

 

T.-..---------—----

l
f
0 It rt Ifi

f] r ' ' I ' ' ' If F.
150 I70 190 210 230 250 270

 

 

v Day of Year

Figure 3.3d. Grain biomass for treatments during 1989. The
region between the vertical dashed lines depicts the deficit
period.

104

husk-silk-cob weight declined for all treatments near the end
of the growing season, whereas leaf weight remained fairly
constant. In general, harvest percentages of total above
ground biomass were 17 %, 22%, 11%, and 50 $5 for leaves,
stems, husk-silk-cobs, and grain, respectively, for all
treatments. Hall et al. (1981) also found no effect of pre-
anthesis water deficits on post silking above ground dry
matter partitioning as compared to fully irrigated plants.
These results suggest that all plant parts are reduced in size
by a soil water deficit that occurs before anthesis.

Figure 3.4 illustrates crop growth rate (CGR) during
1989 for the current study. There was a maximum reduction in
CGR of 55 % and 65 % near the end of the deficit period for
PAD P1 and PAD P2 plants, respectively, compared to the
control. After irrigation resumed, CGR for PAD P1 plants
remained 18 % less than I P1 plants, and CGR for PAD P2 plants
remained 26 % less until DOY 230. This marked the end of the
linear biomass accumulation period. In comparison to these
results, Lorens et al. (1987) observed a 12 9s to 15 96
reduction in CGR during the linear biomass accumulation period
caused by a 12 day water deficiency.

Examination of CGR alone did not define the cause of
biomass reductions. McCree (1986) indicated that leaf
expansion reductions due to stress were important for whole-
plant carbon balance. Details of leaf growth for the current

study were discussed in a companion paper, however, Figure 3.5

105

 

A
7' 5° *F
-‘e—olP1'
5‘ 45 s—aPADFiI
'0 HPADRZ
4D '

U
01

------------

 
 
 

 

N
U'I

(A
O
LlllllllLJAlJLLLllllllllij‘leAlll I

N
O

 

 

 

Crop Growth Rate (gms m
Bi

I I I U r I V I U I l fi W f l

150 150 190 (zio' 230 250 270
Day of Year

Figure 3.4. Above ground crop growth rate (CGR) for
treatments during 1989. The region between the vertical
dashed lines depicts the deficit period.

 

106

 

     

 

 

 

7.0 r u
1 9-0 IP1 : :
A I a—a PAD 91 I
T 5-01 H PAD d2 1
4 . ~
E 50:
CV I ° :
é :
4.0-
x q
a, J
13 ‘ I
E 3.04; :
8 1 i
L- 20; I
< - . .
u— ‘ I
a I '
a, _ I
y I I
a I I
0.0 r r I I 1r r 1—IL1’r T I t I t I 1 I l I I I I I
1 50 170 190 21 0 230 250 270

Day of Year

Figure 3.5. Leaf area index (LAI) for treatments during
1989. The region between the vertical dashed lines depicts
the deficit period.

107

delineates leaf area index (LAI) for the treatments during
1989. There was a marked difference caused by the PAD
treatments, and this remained after irrigation had resumed.
Senescence was not different due to the deficit period, in
fact, PAD plants seemed to maintain green leaf area longer
late in the season. Hall et al. (1981) and Lorens et al.
(1987) reported leaf area reductions of 13 % and 35 96,
respectively, due to vegetative water deficits. In addition
to water deficit influence on leaf area, Greenwood (1976)
proposed that leaf growth in monacots was a sensitive
indicator of nitrogen, deficiency. Wolfe et al. (1988)
observed 30 % reductions in green leaf area over two years for
water deficit and nitrogen deficit plants alike.

Net assimilation rate (NAR) accounts for differences in
crop growth rate due to leaf area. Figure 3.6 illustrates
NAR for treatments during 1989. Whereas maximum CGR
reductions were 55 % to 65 % for PAD plants as compared to
the control, maximum NAR reductions were only 40 % to 45 %
near the end of the deficit period. Also, after irrigation
resumed there was little difference between NAR among
treatments. Radin (1983) reported a 25 % decrease in NAR for
barley resulting from decreased leaf area. The lack of leaf
area in that experiment was caused by a reduction in nitrogen
accumulation rate rather than by a water shortage.

While NAR assessment in the current study explained some

of the differences in above ground biomass accumulation, there

108

1>

 

3‘ §3L33.3i
133v
EEiETE
32-

 

 

 

q--------

 

 

V U I

250 2io'

 

Net Assimilation Rate (gms mm2 day
‘1”

Day of Year

Figure 3.6. Above ground net assimilation rate (NAR) for
treatments during 1989. The region between the vertical
dashed lines depicts the deficit period.

109

was still a substantial reduction in this value for PAD
treatments. This would seem to suggest a reduced
photosynthetic capacity for the water deficit plants, however,
this was not believed to be the case. Figures 3.7a and 3.7b
show leaf rolling on three successive clear days for the PAD
plants during the deficit of 1989. The rolled width was on
average 50 % to 60 % less than the fully open width. All
leaves were not measured, but if one assumes an overall
rolling of 40 %, and also takes into account the change in
leaf angle, then the "effective LAI" would have been
considerably less than that measured" 'This could have
accounted for the difference in NAR values without loss in
photosynthetic capacity. A midday light interception
assessment on 7 July (DOY 188) indicated 25 % to 30 % of the
light measured above the canopy was intercepted by PAD plants
as compared to 65 % to 70 % by I P1 plants. Jordan (1983)
cited a light interception value of 52 % for water deficit
sorghum plants as compared to 96 % for irrigated plants. He
discussed. the beneficial role of leaf rolling as being
twofold: (i) less radiation load due to smaller exposed leaf
area, and (ii) less transpiring surface. He indicated more
research was needed to quantify the influence on crop growth.

The effects of above ground biomass production have been
considered thus far. Figures 3.8a through 3.8a depict root
growth.before (DOY 166), during (DOY 182), and after (DOY 203)

the water deficit period during 1988. A decrease in root

110

d

[2:] Leaf 10
90 E Leaf 11
ZZZ Leaf 12

      

Day 186 Day 187 Day 188

Leaf Rolling (rolied width/unroiled width x 100)

Figure 3.7a. Leaf rolling for leaves 10, 11, and 12 of pre-

anthesis deficit plants of the first planting date during
1989.

111

§

 
   

[:3 Leaf 10
E Leaf 11
EB Leaf 12

8

(D

Day 186 Day 187 Day 188

Leaf Roiiing (roiled width/unrolled width x 100)

Figure 3.7b. Leaf rolling for leaves 10, 11, and 12 of pre-

anthesis deficit plants of the second planting date during
1989.

112

 

 

 

A 2.4
N ‘ o-o Irrigated

I 22" a—a PAD

§ 2.0-

% 1.8-:

%; ‘LB:

2 1.4-

8 1.2-

13 .

:3 ‘L0:

3,; 0.8-

2 0.6- .

Q) ‘ .

o 0.4- .- - .

u . .

o 0.2‘ ' ~<
C) . -' ' .

 

0.01011VOI2j0I3TOI4‘OI5'0f6‘OJ 0.3 0.9 1.0 1.1
Soil Depth (m)

Figure 3.8a. Minirhizotron root observations for irrigated

and pre-anthesis deficit plants on DOY 166 in 1988. This
was before the deficit period.

113

 

o—o Irrigated
I 22‘ a—a PAD

 

Root Density (observations cm
23
l

0.0 .waw .- ., 1— .
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
Soil Depth (m)

 

 

 

Figure 3.8b. Minirhizotron root observations for irrigated
and pre-anthesis deficit plants on DOY 182 in 1988. This
was during the deficit period.

)

Root Density'(observations cm

' 0.8:

N
...

114

 

2.2:
2.o~

J
1.84
1.6-1
1.4-
1.2-
1.0a

0.6-
0&4"

J
0.2-

0-0 irrigated
s—a PAD

 

\

..l

 

 

0.0

0.

Figure 3.8c.

and pre-anthesis deficit plants on DOY 203 in 1988. This
was after the deficit period.

 

' 1 r i "r r I r r 1*1‘3 l ”I 3*1 ' u '
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
Sail Depth (m)

Minirhizotron root observations for irrigated

115

observations in the upper 0.3 m of soil was present during
the deficit period, along with a substantial increase in roots
from 0.4 m to 0.8 m for PAD plants. Examination of the whole
profile indicated a net increase in root observations for the
PAD plants overall during the deficit period as compared to
I plants. Thus, a greater percentage of carbon was allocated
to the root system during the deficit period. This could have
accounted for some of the observed differences in above ground
biomass accumulation reported earlier. After the deficit
period the root distribution became more similar, although,
the PAD treatment still had less roots from 0.2 m to 0.3 m.

Increased root proliferation at deeper depths and
decreases in the surface soil in response to water deficits
has been observed by several researchers, including
unpublished data of the current authors. Hoagenboom et al.
(1987) demonstrated nonirrigated soybeans produced more roots
at depths of 0.6 m to 1.4 m than irrigated soybeans. Mayaki
et al. (1976) reported both soybeans and corn produced more
roots from 0.9 m to 1.5 m under nonirrigated conditions than
under irrigated conditions. They observed a 70 % reduction
in corn yield with only a 25 % reduction in total root weight.
Thus, the shoot to root ratio was not the same under water
deficit conditions. Further, Sharp and Davies (1979)
confirmed a rapid decrease in leaf extension with a
simultaneous increase in root length and dry ‘weight in

response to a water shortage. These various results suggest

116
that reports on shoot to root ratios for corn by Foth (1962)
and Fairey and Daynard (1978) under more normal conditions
cannot be used to estimate whole plant carbon balance under
a diversity of environments and stress conditions.

Data presented thus far have indicated similar responses
of 'water' deficit. plants and. those experiencing' nitrogen
shortages. These factors cannot be considered independently,
especially under field conditions. Sanchez et al. (1982)
indicated that the whole-plant nitrogen uptake was sensitive
to water deficits. The reduced surface rooting and water
uptake under deficit conditions as described in the current
study and companion.papers should.have had an influence on the
nitrogen status of plants. Observations by the current
authors over several years in the field have indicated plants
suffering from pre-anthesis water deficits were also suffering
from nitrogen problems. Invariably, after irrigation resumed
plants would remain pale-yellow for three to four days as
though there were nitrogen deficiencies. In order to evaluate
this, plants were sampled in 1989 for nitrogen content on 31
July (DOY 212), which was about a week after anthesis of
irrigated plants. In addition, grain nitrogen uptake was
monitored through three subsequent samplings.

Figures 3.9 and 3.10 depict whole-plant nitrogen and
grain nitrogen, respectively, for all treatments. There was
no significant difference in percent nitrogen for the

treatments other than. An exception was grain nitrogen of

117

'8

Nitrogen Content (7.)

O

 

0.00

Total Stem Leaf Ear
Plant Part

Figure 3.9. Above ground plant nitrogen content (%) and

distribution in leaves, stems, and ears for all treatments
on DOY 212 in 1989.

118

2.50
2.25
2.00
1 .75
1 .50
1 .25
1 .00
0.75
0.50
0.25
0.00

Grain Nitrogen Content (75)

 

Day 227 Day 249 Harvest

Sampling Date

Figure 3.10. Grain nitrogen content (%) on DOY 227, DOY
249, and at harvest (DOY 270) for all treatments in 1989.

119

PAD P2 plants on DC! 227. Grain for this treatment on this
date was small and not very developed as PAD P2 plants were
the latest flowering (see NeSmith et al., 1990b). Therefore,
nitrogen constituted a greater percentage of the grain dry
weight. Total nitrogen by weight was dissimilar for
treatments as it was proportional to the differences in
biomass. The final amount of grain nitrogen (on a weight
basis) was similar to that amount in the above ground portion
of the plant when sampled on DOY 212. The exception was the
PAD P2 treatment, which apparently had additional uptake that
was to become grain nitrogen under this treatment. Again,
this was the latest flowering treatment. These results
compare to those of Hanway (1962b) and Friedrich and Schrader
(1979) who reported that the nitrogen amount in the grain at
harvest was nearly that present shortly after silking.

Wolfe et al. (1988) observed no difference in nitrogen
uptake at anthesis and at the end of the growing season for
water deficient and nitrogen.deficient plants, although, both
were different from plants which received adequate water and
nitrogen. Davies et al. (1986) postulated an interactive
effect between nutrient supply and root cytokinin supply on
shoot growth rate. These results and those of the current
study indicate that a major influence of pre-anthesis water
deficits may be on the nitrogen uptake of plants, and that

this has resulting effects on biomass production. Dry weight

120
was proportional to the amount of nitrogen and so was yield
and grain number as reported in a companion paper.

Hawkins and Cooper (1981) concluded from examination of
several sets of data that grain number, and thus yield, of
corn was determined by pre-flowering growth rate. They
indicated that a static value of plant size was also
correlated with grain number, however, they argued that the
dynamic process of grain number determination would not be
linked to such a fixed value. They further postulated that
a mechanism yet determined was responsible for the influence
of biomass accumulation on grain number. The current results
suggest that nutrient uptake and status of plants may be
linked to such a mechanism. The quantification here is not
enough to merit a conclusion as to this. Additional research
on water deficit influence on nutrition of plants is needed,
especially in the area of nitrogen acquisition and how pre-

anthesis water deficits influence this.

LIST OF REFERENCES

Brown, R.H. 1984. Growth of the green plantw In Tesar (ed.)
Physiological basis of crop growth and development. pp. 153-
174. American Society of Agronomy, Madison, WI.

Claassen, M.M. and R.H. Shaw. 1970. Water deficit effects
on corn. I. Vegetative components. Agron. J. 62: 649-652.

Davies, W.J., J. Metcalfe, T.A. Lodge, and A.R. da Costa.
1986. Plant growth substances and the regulation of growth
under drought. Aust. J. Plant Physiol. 13: 105-125.

Denmead, O.T. and R.H. Shaw. 1960. The effects of soil
moisture stress at different stages of growth on the
development and yield of corn. Agron. J. 52: 272—274.

Fairey, N.A. and T.B. Daynard. 1978. Quantitative
distribution of assimilates in component organs of maize
during reproductive growth. Can. J. Plant Sci. 58: 709-717.

Ferguson, J.C. and A.J.M. Smucker. 1989. Modifications of
the minirhizotron video camera system for measuring spatial
and temporal root dynamics. Soil Sci. Soc. Amer. J. 53:
1601-1605.

Foth, H.D. 1962. Root and top growth of corn. Agron. J.
54: 49-52.

Friedrich, J.W. and L.B. Schrader. 1979. N deprivation in
maize during grain-filling. II. Remobilization of u N and
35 S and the relationship between N and S accumulation. Agron.
J. 71: 466-472.

Friedrich, J.W., L.B. Schrader, and E.V. Nordheim. 1979. N
deprivation in maize during grain-filling. I. Accumulation
of dry matter, nitrate-N, and sulfate-S. Agron. J. 71: 461-
465.

121

122

Grant, R.F., 8.8. Jackson, J.R. Kiniry, and G.F. Arkinn 1989.
Water deficit timing effects on yield components in maize.
Agron. J. 31: 61-65.

Greenwood, E.A.N. 1976. Nitrogen stress in plants. Adv.
Agron. 28: 1-35.

Hall, A.J., J.H. Lemcoff, and.N. Trapani. 1981. Water stress
before and during flowering in maize and its effects on yield,
its components, and their determinants. Maydica XXVI: 19-
38.

Hanson, A.D. and W.D. Hitz. 1983. Whole-plant response to
water deficits: Water deficits and nitrogen economy. In
Taylor, Jordan, and Sinclair (ed.) Limitations to efficient

water use in crop production. pp. 331-343. ASA, CSSA, SSSA,
Madison, WI.

Hanway, J.J. 1962a. Corn growth and composition in relation
to soil fertility: I. Growth of different plant parts and
relation between leaf weight and grain yield. Agron. J. 54:
145-148.

Hanway, J.J. 1962b. Corn growth and composition in relation
to soil fertility: II. Uptake of N,P, and K and their
distribution in different plant parts during the growing
season. Agron. J. 54: 217-222.

Hanway, J.J. and‘W.A. Russell. 1969. Dry-matter'accumulation

in corn (2;; gays L.) plants: Comparisons among single-cross
hybrids. Agron. J. 61: 947-951.

Hawkins, R.C. and P.J.M. Cooper. 1981. Growth, development,
and grain yield of maize. Expl. Agric. 17: 203-207.

Hoagenboom, G., M.G. Huck, and C.M. Peterson. 1987. Root
growth rate of soybean as affected by drought stress. Agron.
J. 79: 607-614.

Johnson, D.R. and.J.W. Tanner; 1972. Comparison of corn (Lg;
mays L.) inbreds and hybrids grown at equal leaf area index,
light penetration, and population. Crop Sci. 12: 482-485.

Jordan, W.R. 1983. Whole plant response to water deficits:
An overview. In Taylor, Jordan, and Sinclair (ed.)
Limitations to efficient water use in crop production. pp.
289-317. ASA, CSSA, SSSA, Madison, WI.

123

Karlen, D.L., R.J. Sadler, and C.R. Camp. 1987. Dry matter,
nitrogen, phosphorus, and potassium accumulation rates by corn
on Norfolk loamy sand. Agron. J. 79: 649-656.

Kevlen, H.V. 1981. Modelling the interaction of water and
nitrogen. Plant Soil 58: 205-229.

Linvill, D.R., R.F. Dale, and H.F. Hodges. 1978. Solar
radiation weighting for weather and corn growth models.
Agron. J. 70: 257-263.

Lorens, G.F., J.M. Bennett, and L.B. Loggale. 1987.
Differences in drought resistance between two corn hybrids.
II. Component analysis and growth rates. Agron. J. 79: 808-
813.

Mayaki, W.C., L.R. Stone, and I.D. Teare. 1976. Irrigated
and nonirrigated soybean, corn, and grain sorghum root
systems. Agron. J. 68: 532-534.

McCree, K.J. 1986. Whole-plant carbon balance during osmotic
adjustment to drought and salinity stress. Aust. J. Plant
Physiol. 13: 33-43.

NeSmith, D.S., J.T. Ritchie, and A.J.M. Smucker; 1990a. Pre-
anthesis soil water deficit effect on corn (Zea mayg L.). I.
Vegetative growth and development. (companion paper).

NeSmith, D.S., J.T. Ritchie, and A.J.M. Smucker. 1990b. Pre-
anthesis soil water deficit effect on corn (flea mays L.). II.
Reproductive growth and development. (companion paper).

Radford, P.J. 1967. Growth analysis formulae - their use
and abuse. Crop Sci. 7: 171-175.

Radin, J .W. 1983. Control of plant growth by nitrogen:
Differences between cereals and broadleaf species. Pdant,
Cell, Environ. 6: 65-68.

Radin, J.W. and J.S. Boyer. 1982. Control of leaf expansion
by nitrogen nutrition in sunflower: Role of hydraulic
conductivity and turgor. Plant Physiol. 69: 771-775.

Rhoads, F.M. 1984. Nitrogen or water stress: Their
interrelationships. In Hauck (ed.) Nitrogen in crop
production. pp. 307-317. ASA, CSSA, SSSA, Madison, WI.

 

124

Sanchez, R.A., A.J. Hall, N. Trapani, and R. Cohen de Hunau.
1982. Effects of water stress on the chlorophyll content,
nitrogen level, and photosynthesis of leaves of two maize
genotypes. Photosynthesis Res. 4: 35-47.

Sharp, R.B. and W.J. Davies. 1979. Solute regulation and
growth by roots and shoots of water-stressed maize plants.
Planta 147: 43-49.

Tsai, C.Y., D.M. Huber, D.V. Glover, and H.L. Warren. 1984.
Relationship of N deposition to grain yield and N response of
three maize hybrids. Crop Sci. 24: 277-281.

Upchurch, D.R. and J .T. Ritchie. 1984. Battery-operated
color video camera for root observations in mini-rhizotrons.
Agron. J. 76: 1015-1017.

Verasan, V. and R.B. Phillips. 1978. Effects of soil water
stress on growth and nutrient accumulation in corn. Agron.
J. 70: 613-618.

Wolfe, D.W., D.W. Henderson, T.C. Hsiao, and.A. Alvino. 1988.
Interactive water and nitrogen effects on senescence of maize.
I. Leaf area duration, nitrogen distribution, and yield.
Agron. J. 80: 859-864.

CHAPTER 4

EFFECTS OF SOIL WATER DEFICITS DURING ANTHESIS
ON FIELD GROWN CORN (ZEA MAXS L.)

Water deficits during flowering and pollination are the
most devastating to yields, especially those of determinate
crops such as corn. The objective of this research was to
gain a clearer understanding of how intermittent soil water
deficits influence.emergence of tassels and silks and what the
resulting effects on yield and yield components were. A rain
shelter was utilized to provide timely water deficits in a
field environment during 1987 and 1988 on a sandy soil in
Michigan. Yield reductions in excess of 90 % occurred when
a water deficit spanned the interval from floral component
emergence to beginning grain fill. Delayed emergence of
tassels and silks greater than two weeks was observed for some
water deficit plants. Water deficit treatments that impacted
plant extension growth such that emergence of tassels was

delayed until irrigation resumed were less detrimental than

125

126
deficits treatments in which there was tassel exposure. Grain
number was the yield component consistently reduced by the
intermittent water deficits, and there was both reductions and
increases in grain weight depending on the deficit severity

and timing.

ODUC ON

Water deficits during or shortly after anthesis are
considered to be among the most devastating to grain yields,
especially for determinate species such as corn (Begg and
Turner, 1976). Consistent observations of yield reductions
in excess of 50 % have been reported for several experiments
using plants grown in containers, and grain number has been
the primary component affected (Claassen and Shaw, 1970:
Denmead and Shaw, 1960: Grant et al., 1989: Hall et al.,
1981) . The lack of grain number due to water shortages during
flowering has been attributed, in part, to poor
synchronization in emergence of male and female flower
components (Freier et al., 1984: Hall et al., 1982: Herrera
and Johnson, 1981).

Field water deficit experiments are difficult to conduct
in more humid regions due to the untimeliness of rain.
However, field research is needed in order to verify responses
of crops grown in container systems. Rain shelters along with

controlled water applications can reduce precipitation

127
interferences and provide judicious scheduling of crop water
supply in field environments (Foale et al., 1986: NeSmith et
al., 1989: Upchurch et al., 1983). The objective of the
experiments reported here was to utilize a rain shelter to
impose soil water' deficits during anthesis of corn and
determine the influence on flowering, yield, and yield

components.

ALS AND METHODS

This research was conducted during 1987 and 1988 at the
Kellogg Biological Research Station near Kalamazoo, Michigan,
USA. Corn was grown in an area that could be covered by a
rain shelter when needed. This facility has been described
elsewhere by Martin et al. (1988). The soil was a Spinks sand
(sandy; mixed, mesic Psammentic iHapludalf). Figure 4.1
illustrates the water content of the soil profile after near
saturation followed by three days of drainage and after more
than forty days of drying by a corn crop with no additions of
water. The rain shelter did not cover plots from September
to April each year, and as a result the soil water profile was
near the drained status at the beginning of the growing season
because of snow and rain.

During 1987 a completely randomized experimental design
with two replications was used. Great Lakes hybrid 599 was

planted in 4.3 m x 6.2 m plots on 12 May (day of year,

128

 

 

 

 

 

0.25 .
"1“ fl "' DQISGI
I i - - Drained Sail
EE .
LI
n
E
L)
V
*1
Cl
C)
+a
CI
0'
o
L.
G)
Jul
C3
. 3
'6 I
m .
00m ' r I U I j r r V I I I r T I I Y 7r ' I 1 1 j r
0.0 0.5 1.0 1.5 2.0 2.5

Soil Depth (m)

Figure 4.1. Soil water content of a Spinks soil at
different depths after saturation followed by three days

drainage and after more than forty days of drying by a corn
crop.

129
DOY 132) in 0.71 m rows at a depth of 0.05 m. The plants

emerged on 17 May and were thinned two weeks later to a

was at a rate of 15 kg ha‘1 N, 60 kg ha'1 K, and 15 kg ha"1 P. 1

Additional nitrogen was applied at a rate of 120 kg ha‘1 N and

90 kg ha'1 N on 24 June and 1 July, respectively. Irrigation

\.

population of 8.3 plants mi. Fertilizer applied at plantingii

'l
l

l

i
l

'l

regimes of the various treatments were as follows:
Treatment 1 - Irrigated as depicted in Figure 4.2.
Treatment 2 - Not irrigated between 11 July (DOY 192)
and 23 July (DOY 204).
Treatment 3 - Not irrigated between 11 July (DOY 192)

and 30 July (211).

Treatment 4 Not irrigated between 11 July (DOY 192)
and 17 August (DOY 229).

Treatments 2 through 4 received an initial 40 mm of water when
irrigation resumed. Other than this one application the
irrigation schedule of treatment 1 was followed for these
treatments except during the deficit period. On 5 October,
1987 a 6.5 n? area was harvested for each plot. Plants with
and without ears were counted to determine barrenness. Yield
was calculated on a per plant basis from a composite sample,
and yield components were determined from.a subsample of ears.
These ears were oven dried at 60 °C and grain was removed

manually, after which it was weighed and grain number was

counted.

l

l
I

l

130

 

     

Irrigation Amount (mm)
N
01
Lilli l

o: i ,, ,..+,+.,fl,..
120 1:55 180 95 21 225 240 255 270

 

 

 

 

Figure 4.2. Irrigation amounts applied to treatment 1
during 1987.

131

During 1988 a completely randomized split-plot
experimental design with one replication was used in which
water regime was the main plot and corn cultivar was the sub-
plot. Main plot size was 4.3 m x 6.2 m. Pioneer corn hybrids
3540 and 3475 were planted at a higher than desired density
on 5 May (day of year, DOY, 126) in 0.71 m rows at a depth of
0.05 mm 'These hybrids were chosen because there had been some
observed differences between them in response to drought
during certain years but not others. Part of this
investigation was to determine potential reasons for such
variability. Emergence occurred on 15 May, and plants were
thinned to a population of 7.9 plants :mq' on 25 May.
Fertilizer applications were 150 kg ha"1 K on 20 April, 60 kg
had'N on 25 May, 300 kg haq'P and 160 kg haq'N on 6 June, and
75 kg ha’1 N on 15 July. There were two water regimes, an
irrigated control (I) and a flowering water deficit (FD).
Water applications were the same for treatments except during
the deficit period (Figure 4.3).

Plant measurements during 1988 included silking
determination which was made on eight sample plants per plot.
Silking was declared as the day when there were any visible
silks for a respective plant. A compound measurement of
elongation of husks, shanks, and ears (referred to as intact
ear length) was determined for the eight sample plants. A
point of reference was marked on.a stem at the node just above

where an ear was attached to the plant, and length was

132

 

2463551 '270

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Ev
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iff‘iilarfil’iii I‘
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P ivrril‘fliflflifl%
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iriff’lrfilfifllf
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aiifl’vf‘Jiffilrif
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mm “w nu Ru nU Eu nu Ru nu

1a 0‘ at
AEEV acaoE< cozooE.

Day Of Year

Irrigation amounts applied to treatments during

The region between vertical dashed lines represents
the period when no water was applied to flowering deficit

(FD) treatment.

Figure 4.3.
1988.

133

determined by recording the distance between the reference
point and the tip of the visible husk. (M1 19 September 1988,
four plants were harvested in each sub-plot from which yield,
grain number, grain weight, and harvest index were determined.
Ears and plants were separated and were placed in an oven at
60 °C for four days. After drying, grain was removed from
each ear manually and was weighed and grain number counted.
Barren plant number was determined in each plot from the
entire population.

Soil water content was measured during 1988 using the
neutron scattering technique. Sampling was in 0.25 m
increments to a depth of 1.5 m, and there was one access tube
in the center row of each sub-plot“ Measurements began.during
mid-vegetative growth and were taken one or two times weekly.
The water content during the deficit period was plotted and
a line fitted through the data for each sampled depth. The
slope of this line was taken as water absorption rate,

assuming negligible flow.

BESULT§ AND DISCUSSION

Table 4.1 depicts results from the 1987 experiment. The
water deficits began just before tassel emergence of treatment
1 plants. Cessation of extension growth of deficit plants
caused delayed tassel and silk emergence. When irrigation

resumed for treatments 2 and 3 emergence of tassels and silks

134

Table 4.1. Silking date, yield, grain number, grain weight,
and percent barren plants for treatments during 1987.

 

Treatment Number

 

1 2 3 4
75 % Silking 201 207 213 --- +
(Day of Year)
Yield * 88 69 46 26
(gms plant”) (7.7)** (7.5) (6.4) (8.8)
Grain Number 452 362 194 105
per Ear (33.7) (25.8) (24.9) (18.4)
Grain Weight 194 190 238 244
(mg seed”) (6.6) (9.6) (12.8) (52.1)
Barren Plants 7 8 4 80
(%)
Yield Based on 8039 6235 4338 511
Land Area ***
(kg ha“)

 

+ This treatment never achieved 75 % silking.
* Only plants with ears were used to calculate.

** Values in parenthesis () are standard errors of means
with n = 10 except treatment 4 where n = 6.

*** Calculated as 15.5 % moisture.

135

occurred within 2 to 3 days. Treatment 4 was under deficit
conditions long enough that only a few plants eventually
flowered. prior to resuming' irrigation. ‘When irrigation
resumed for treatment 4 tassels and silks emerged rapidly as
with other treatments, yet there was little pollen produced
by the tassels of these plants. Less than 50 95 of the
treatment 4 plants produced any silks. Delayed silk emergence
of 1 to 8 days has been reported by other researchers in
response to water deficits during or just prior to anthesis
(Grant et al., 1989: Herrera and Johnson, 1981; Hall et. al.,
1981: Robins and Domingo, 1953: Vincent and Woolley, 1972).
As with the current study, the length of the delay in these
experiments depended on the duration and degree of the
deficit.

Although treatment 1 was irrigated the mast, it did not
receive as much water as it needed due to problems with the
irrigation system. Therefore, its yield was less than that
observed for this and other cultivars under well-watered
conditions in other' years. Irrigated corn yields have
averaged around 110 gms plant'1 on this soil at the plant
population and fertilizer rates used. Yield losses due to
delayed flowering can be determined from these data, however.
Reductions in yields for treatments 2 and 3 on a per plant
basis were 22 % and 47 9s, respectively, as compared to
treatment 1. This corresponded to 6 and 12 day delays in

silking for these treatments. Treatment 4 resulted in 80 %

“v-31. D”;- M “Inn-.4... .—

136
barren plants, and even those with ears had drastic yield
reductions. Calculations on a land area basis for treatment
4 showed more than a 90 % reduction in yield as compared to
treatment 1.

Grain numbers during 1987 were reduced for the deficit
treatments relatively proportional to the delayed flowering.
This was not the case with grain weights. Average grain
weights for treatment 2 was not different than that of
treatment 1, however, treatments 3 and 4 had increased weights
of 25 %. The increased weights for the late flowering
treatments were somewhat of a compensation for the excessively
law grain numbers. These results agree with those of several
aforementioned investigations in that grain number was the
most affected parameter by the water deficits.

Results from the 1988 experiment differed somewhat from
those of the 1987 experiment. The water deficits hastened
beginning silk emergence slightly for both hybrids, however,
3540 FD plants did not exceed 75 96 silk emergence until
irrigation resumed (Figure 4.4). These influences on silking
were due to the developmental stage at which deficits caused
stress in the FD plants. The plants for 1988 overall were
closer to anthesis when the deficit began than were those in
1987, and hybrid 3475 was closer to anthesis than hybrid 3540
when the deficit began in 1988.

Intact ear measurements demonstrated results similar to

that of silking data for 1988 (Figure 4.5). Ear growth was

137

 

 

'22s

 

 

100-
904 a
o 80‘ :
0’. q ' r: :
3 70- ;
C « g
8 60- .‘~
I; ‘ l .’
‘1 5°: ::
.3 ‘°‘: :' :'
S :50- .’ .'
l" « :: ~
20- I r c H 3475 F0
. i i i H 3475:
10- .l ,' ,' a—a 3540 F0
‘ {j 1' 9-0 3540 l
0‘ l I ‘1 1 l' ij I I 1 j I I j I 1 j rj U
195 200 205 210 215 220
Day of Year
Figure 4.4. Silking percentage of treatments as a function

of time during 1988.

138

 

 

 

 

22
1 0435401
2019-9354010
A 18- H 34751
E . e-e 3475FD
éfl 15:
5 14-
? 4
0 12-
J I
L. 10-
0 J
Lu 3-
8 ‘ x
O 6- I: -1 (y
«H ‘ I /
E. 4- 1'
J I
2" I 1’!
I II
‘ I II
0- '{#...,.r..,....T....
195 200 205 210 21 5 220
Day of Year

Figure 4.5.

Intact ear length of treatments as a function

of time during 1988.

 

225

139

greater for 3475 FD plants than for 3540 PD plants as the
latter treatment was just beginning rapid ear elongation when
the water shortage caused extension growth reductions. These
results indicate the importance of considering developmental
stage of the plants in conducting water deficit experiments,
especially when comparing different cultivars. It is
imperative that even slight differences in development be
accounted for.

Water absorption rates at different soil depths for FD
treatments during the deficit period of 1988 are depicted in
Figures 4.6a and 4.6b. There was a rapid decline in water
absorption rate at the 0.00 m to 0.25 m depth paired with a
slight increase at the 0.25 m to 0.50 m depth shortly after
water was withheld. Water absorption rates at the other
measured depths remained nearly constant. Figure 4.7
demonstrates that transpiration was sustained by water
absorption from the upper 1.5 m of soil until around DOY 203.
The magnitude of the water deficit can be determined by
comparing these results with those of another experiment
(NeSmith. et al., 1990) in. which. plant extension. growth
essentially ceased when the surface soil water absorption.rate
reached a value of 3 (water absorption rate units).

Table 4.2 depicts harvest data for the 1988 experiment.
The harvest index values reflected there were large plants
with small ears under deficit conditions indicating there was

no appreciable influence on vegetative growth. Yield

140

 

14
13; 0—0 0.00to 0.25m

a) O «a—aO.25toO.50m

*5 8 121H0.50 to 0.75m

01 .- 11-

C >< -

.9 A10.

‘é'l' 9‘. x.

O )N 8'

3 ° 71

'o

<[ 6:

L.V3 ‘

3' 54

o E « -‘

g o 4- . ‘

an 3- ‘ .

8 s - - = = .

0 2" C ..

O: V 1. . . . . 1' §\

0 I I IT I Ufilj I If! I fl 1' I I ' T—F

 

 

 

' l
194 197 200 203 206 209 212 215 218
Day of Year

Figure 4.6a. Water absorption rates at depths of 0.00 to
0.25 m, 0.25 to 0.50 m, and 0.50 to 0.75 m during the deficit
period for the flowering deficit treatment during 1988.

141

 

 

 

14
13... 0-0 0.75t01.00 m
o O «Ia-91.00t0125m
*5 8 ‘21H1.25t01.50m
CK P11-
c
.9 : 10f
"é'.’ 9‘-
C> >~ 8:
i3 " 7~
.0
< 6;
t") .
3' 5-1
a E 4
g o 4-
Ens 3':
O o 2-
a: v .
‘1 M
o I I I I I I r I I I I I ‘

 

194 197 zaor 1253' 206 '269 212 215 213
Day of Year

Figure 4.6b. Water absorption rates at depths of 0.75 to
1.00 m, 1.00 to 1.25 m, and 1.25 to 1.50 m during the deficit
period for the flowering deficit treatment during 1988.

142

 

o—o Potential
9- a—a Measured

)

—1

Evaporation Rate (mm day

 

 

 

 

o I I I I I T I f

194 197 1260' 203 206 T262; 212 21r5 213
Day of Year

Figure 4.7. Potential evaporation and measured total water
absorption from the 1.5 m soil profile during the deficit
period for the flowering deficit treatment during 1988.

Table 4.2.
barren plants,

143

Grain yield, grain number, grain weight, percent
and harvest index for treatments during 1988.

 

 

 

Treatments

3540 I 3540 FD 3475 I 3475 FD
Grain Yield 128 29** 115 38**
(gms plant“) (11.9)* (10.0) (6.4) (11.1)
Grain Number 469 176** 519 287**
per Ear (40.4) (58.6) (69.4) (86.1)
Grain Weight 272 165** 222 133**
(mg seed“) ( 8.0) (14.5) (31.0) (22.1)
Barren Plants 0 15 0 40
(%)
Yield Based on 11,967 2305 10,751 2132
Land Area
(kg ha“) ***
Harvest Index 0.56 0.24** 0.53 0.32**
* Values in parenthesis () are standard errors of means

with n = 4.

** Only plants with ears were used in this calculation.

*** Calculated as 15.5 % moisture.

144

reductions for FD treatments as compared to their respective
controls were similar to the reductions caused by treatment
4 during 1987. On an area basis yields were 80 % less for
the FD treatments. Both grain number and average grain weight
were reduced. This was due to the deficit extending into the
grain filling period which has been shown to be a time when
grain weights are most reduced by stress (Grant et al., 1989;
Jurgens et al., 1978; NeSmith and Ritchie, 1990: Westgate and
Boyer, 1985).

Evaluation of results from these two experiments indicate
that flowering is indeed a critical time in which to avoid
water deficits. However, there were more drastic effects on
plants when deficits were experienced during the time when
tassels and silks were exposed, or when emergence of these was
delayed for more than two weeks. If deficits were prior to
emergence of tassel and silks such that these were delayed,
there was some benefit. This may be linked to increased
pollen survival under deficit conditions if the tassel is not
exposed to atmospheric conditions. Further research in this
area would be beneficial.

In summary, results have shown that yield reductions in
excess of 90 % can be caused by water deficits in a field
environment during the flowering period in corn. Delayed
emergence of tassels and silks in excess of two weeks was
observed. Grain number was the most reduced yield component

when water shortages were confined to the fertilization and

145
kernel setting period, however, if the deficit was extended
into the grain filling period average grain weight was reduced
as well. Results indicate that managing irrigation in a
manner that would obtain maximum kernel set through avoidance
of water deficits is necessary to maintain favorable yields
as grain weight compensation is insufficient to off-set loss

of grain numbers.

LIST OF REFERENCES

Begg, J.B. and N.C. Turner. 1976. Crop water deficits. Adv.
Agron. 28: 161-217.

Claassen, M.M. and R.H. Shaw. 1970. Water deficit effects
on corn. II. Grain components. Agron. J. 62: 652-655.

Denmead, O.T. and R.H. Shaw. 1960. The effects of soil
moisture stress at different stages of growth on the
development and yield of corn. Agron. J. 52: 272-274.

Foale, M.A., R. Davis, D.R. Upchurch. 1986. The design of
rain shelters for field experimentation: A review; J. Agric.
Eng. Res. 34: 1-16.

Freier, G., F. Vilella, and A.J. Hall. 1984. Within-ear
pollination synchrony and kernel set in maize. Maydica XXIX:
317-324.

Grant, R.F., 13.5. Jackson, J.R. Kiniry, and G.F. Arkin. 1989.
Water deficit timing effects on yield components in maize.
Agron. J. 81: 61-65.

Hall, A.J., J.H. Lemcoff, and N. Trapani. 1981” Water stress
before and during flowering in maize and its effects on yield,
its components, and their determinants. Maydica XXVI: 19-38.

Hall, A.J., F. Vilella, N. Trapani, and C. Chimenti. 1982.
The effects of water stress and genotype on the dynamics of

pollen-shedding and silking in maize. Field Crops Res. 5:
349-363.
Herrera, M.P. and R.R. Johnson. 1981. Drought stress and

its effects on maize reproduction systems. Crop Sci. 21: 105-
110.

Jurgens, S.R., R.R. Johnson, and J.S. Boyer. 1978. Dry
matter production and translocation in maize subjected to
drought during grain fill. Agron. J. 70: 678-682.

146

147

Martin, E.C., J.T. Ritchie, S.M. Reese, T.L. Loudon, and B.
Knezek. 1988. A large-area, light-weight rainshelter with
programmable control. Trans. Am. Soc. Agric. Eng. 31: 1440-
1444.

NeSmith, D.S., A. Miller, and J.T. Ritchie. 1990. An
irrigation system for plots under a rain shelter. Agric.
Water Management (In press).

NeSmith, D.S., J.T. Ritchie, and A.J.M. Smucker. 1990. Pre-
anthesis soil water deficit effect on corn (Zea mays L.). I.
Vegetative growth and development. (In review).

NeSmith, D.S. and J.T. Ritchie. 1990. Corn (fig; mays L.)
response to an intermittent soil water deficit during grain
filling. (In review).

Robins, J.S. and C.E. Domingo. 1953. Some effects of severe
soil moisture deficits at specific growth stages in corn.
Agron. J. 45: 618-621.

Upchurch, D.P., J.T. Ritchie, and M.A. Foale. 1983. Design

of'a large dual-structure rainout shelteru .Agron. J. 75: 845-
848.

Vincent, 6.8. and D.G. Woolley. 1972. Effect of moisture
stress at different stages on growth: II. Cytoplasmic male-
sterile corn. Agron. J. 64: 599-602.

Westgate, M.E. and J.S. Boyer. 1985. Carbohydrate reserves
and reproductive development at low leaf water potentials in
maize. Crop Sci. 25: 762-769.

CHAPTER 5

CORN (ZEA MAYS L.) RESPONSE TO AN INTERMITTENT SOIL
WATER DEFICIT DURING GRAIN FILLING

ABM

Grain filling is an important growth period to the
economical yield of many crops including corn. Rate and
duration of filling are the two basic components determining
final grain weight, and any alteration of these can be
detrimental to final yield. Research was conducted during
1989 in Michigan utilizing a large rain shelter to impose an
intermittent soil water deficit during the grain filling
period of two commercially grown corn hybrids. Objectives
were to determine the influence on crap and grain growth, rate
and duration of grain filling, grain numbers, grain size
distribution, and final yield as compared to an irrigated
control. Two planting dates and two hybrids provided a range
in the development stage at which deficits were imposed.
Results demonstrated deficit plants had less green leaf area

during grain filling, along with reduced crop and grain

148

149
growth. Crop growth rate was reduced.as much as 67 %, whereas
grain growth rate reductions were only about 30 % for deficit
plants as compared to irrigated control plants. Continuous
single grain samples showed duration of the linear grain
filling phase was shortened by as much as 8 days due to the
water shortages depending on the hybrid and planting date.
One hybrid had reductions in rate of single grain filling of
14 % to 24 % and the other was unaffected for this parameter.
Yield reductions were observed by all treatments experiencing
water deficits and were as great as 40 % loss. Examination
of grain size distributions showed a larger percentage of
seeds weighing less than 100 mg were ontears of deficit plants
along with fewer seeds in the range greater than 200 mg.
Percent nitrogen of the grain was not affected by the paucity
of water, but absolute grain nitrogen was. These results lend
to the importance of managing crop water supply through
irrigation when available in order to avoid water deficits
from flowering until linear grain filling so that maximum

kernel numbers can be achieved.

INIBQDQQIIQN

The period of grain filling is important to the overall
economic yield of grain crops. Johnson and Tanner (1972b)
described three distinct stages in the grain filling process

of corn following pollination. These stages were i) a lag

150

period at the beginning, ii) a linear dry matter accumulation
period, and iii) a leveling off period as maturity approached.
The second stage is commonly referred to as the effective
grain filling period and is considered the most important to
final yield. Duncan (1975) suggested that a simple way to
think of grain yield was to view it as a product of the rate
of photosynthesis during the grain filling period multiplied
by the duration of the period, plus the change in labile
reserves, with grain sink as the upper limit. He pointed out
that this was not entirely correct when the periods of slow
growth (lag and leveling off stages) were considered. In any
case, factors influencing rate, duration, or kernel capacity
impact grain yield.

Several investigations have centered on whether source
(current and stored photosynthates) or sink (kernel number
and filling capacity) limit yield the most during the grain
filling period with mixed results reported (Barnett and
Pearce, 1983; Egharevba et al., 1976: Frey, 1981: Hanway,
1969: Jones and Simmons, 1983: Tollenaar and Daynard, 1978a
and 1978c). In a review on the subject Tollenaar (1977)
indicated that both sink.and source limitations occur and that
combinations of genotypes and environmental conditions
determines the dominant one. An important environmental
factor at any crop growth stage is water supply.

Denmead and Shaw (1960) reported a soil water shortage

during the grain filling period caused a 21 % decrease in

151

yield, and Claassen and Shaw (1970) observed a 30 % yield
reduction in response to a water deficit three weeks after
silking. Jurgens et al. (1978) imposed a terminal drought
stress 10 days after silking and. noticed. a 58 % ‘yield
reduction with 48 % of the loss due to lower grain weight.
Westgate and Boyer (1985) withheld water from plants at early
grain filling (lag stage) and at mid-grain filling and found
yield decreases of 82 % and 36 % for the treatments,
respectively. Grain weight and number were reduced by the
early deficit, whereas only grain weight was reduced by the
mid-grain fill deficit. Grant et al. (1989) determined that
water shortages 16 to 22 days after silking decreased grain
yield 65 % with a 13 % decrease in grain number and a 48 %
decrease in grain weight. When the deficit occurred 22 to 26
days after silking, yield reductions were 47 % and were
attributable entirely to lower grain weight. These various
experiments were with container grown plants and generally
one cultivar was monitored.

In a field experiment with a single cultivar, Robins and
Domingo (1953) observed a 31 95 decrease in yield for a
treatment in which no irrigation was applied after tasseling
when. compared. to) one ‘which. received. three jpost-anthesis
irrigation applications. Investigations involving defoliation
of plants in the field during or shortly after silking have
shown that yields were often reduced similarly to the

aforementioned container water deficit experiments with

152

components responsible being grain size and/or grain number
depending on the hybrid as well as timing and severity of leaf
removal (Barnett and Pearce, 1983: Egharevba et al., 1976:
Frey, 1981: Hanway, 1969: Tollenaar and Daynard 1978c). lsrain
weight reduction due to defoliation stress has been attributed
to decreased rate of filling, shortened duration of filling,
and combinations of both (Hanway, 1969; Jones and Simmons,
1983: Tollenaar and Daynard, 1978c). Decreased grain numbers
have been determined to result from cessation of development
of fertilized kernels caused by stress.during the early stages
of grain filling (Frey, 1981; Kiniry and Ritchie, 1985).

Field water deficit experiments are difficult to conduct
in humid regions due to the untimeliness of rain. This is
especially true when drought during a specific growth stage
is desired. Rain shelters, which reduce the risk of
precipitation interferences, and controlled water applications
can provide judicious scheduling of crop*water supply in field
environments (Foale et al. , 1986: NeSmith et al. , 1989:
Upchurch et al., 1983). The objective of this experiment was
to utilize a rain shelter to impose an intermittent soil water
deficit during grain filling of corn and to determine what
influence there was on crop and grain growth rate, rate and
duration of grain filling, grain numbers, grain size
distribution, and final yield. Two hybrids and two planting

dates provided a range of times during grain filling when

drought occurred.

153

AND

This research was conducted during 1989 at the Kellogg
Biological Research Station near Kalamazoo, Michigan, USA.
Corn was grown in an area that could be covered by a rain
shelter. This facility has been described elsewhere by Martin
et al. (1988). The soil was a Spinks sand (sandy, mixed,
mesic Psammentic Hapludalf) . Figure 5.1 illustrates the water
content of the soil profile after near saturation followed by
three days of drainage and after more than forty days of
drying by a corn crop with no additions of water. The rain
shelter did not cover'plots from.September to April each year,
and as a result the soil water profile was near the drained
status at the beginning of the growing season because of snow
and rain.

A completely randomized split-plot experimental design
was used in which water regime and planting date was the main
plot and corn cultivar was the sub-plot. There were two
replications of each‘treatmentn Pioneer corn.hybrids 3540 and
3475 were used in this investigation because there had been
some observed differences between them in response to drought
during certain years but not others. There were two planting
dates. The reason for this was that there was a difference
in leaf number of one leaf between the two cultivars during
a 1988 experiment. It was hypothesized that this could be

linked to some of the differences in observed responses to

154

 

 

 

0.25 ,
r-s 4 -- DOVSUI
T f -- Drained Soil
E .
C)
n
E
C)
V
4.1
CI
G)
«H
CI
C)
O
L.
Q)
4"
C7
3
.3
0)
Com U T 1 T I T U V FD I r T T I ' V T I U

 

 

. 175 2.0 2.5

0.0 0.5 V 10
Soil Depth (m)

Figure 5.1. Soil water content of a Spinks soil at
different depths after saturation followed by three days

drainage and after more than forty days of drying by a corn
crop.

155

drought, as plants would have been at different developmental
stages during' a ‘water' deficit. period (e.g. hybrid 3475
flowered 2 to 3 days before hybrid 3540) . It was planned that
50 degree days (°Cd) would elapse between the first and second
planting dates to provide a thermal time separation in order
to have hybrid comparisons of plants nearer in development
(i.e. the second planting date of hybrid 3475 would.be similar
in tasseling and silking to the first planting date of hybrid
3540). Water deficits were imposed at the same time for both
planting dates.

Plot size was 4.3 m x 6.2 m, row width was 0.71 m, and
seeding depth was 0.05 m. Planting dates were 3 May (DOY 123,
this will be referred to as P1 indicating first planting) and
17 May (DOY 137, this will be referred to as P2 indicating
second planting) which were separated by 64 °Cd (Figure 5.2) .
Emergence occurred on 18 May and 25 May, and plants were
thinned on 26 May and 30 May for P1 and P2, respectively to
a population of 7.9 plants m4. Fertilizer was applied at a
rate of 63 kg ha'1 N, 230 kg ha'1 P, and 63 kg ha'1 K at
planting. Additional fertilizer applications for P1 and P2
were 96 kg ha'1 N on 1 June, 53 kg ha"1 N on 23 June, and 45 kg
ha"1 N on 20 July. Weeds were controlled manually. There were
two water regimes, an irrigated control (I) and a grain
filling water deficit (GFD) . Water applications were the same
for treatments except during the deficit period (Figure 5.3).

The GFD began on DOY 217 and ended on DOY 236. This

156

 

j ‘."" 1989 P1
1800-: ---- 1989 P2

Thermal Time After Planting (°Cd)
3
CD
.?..

 

 

 

T7T TYr 'TIYUr'T'jr

40 100 "150 200 220 240 260 280

 

O- +1....rr
120 1

Day of Year
Figure 5.2. Thermal time accumulation during 1989. There

were two planting dates (P1 and P2). Units were calculated
using 8 °C as base temperature.

157

 

 

5
5 .

 

Inll'llol'l‘l'Illl'l

||"lllllll|lll|ll‘

I‘ll'llllllll'll'llll
Il‘ll'l'lll'llllllll‘ll

I'll'll'-“ln||ll|lll|||l.'

Illl.‘l|l'|l|l"I'IIIII'III‘IIIII'I’IIIII

I'lll'lllll'le'l'lllaII-I'l

llllll'lll!l1|.

280

260

 

UI‘rTT

140 160

120

05050505050
11

5 4. 4. 3 3 2 2
AEEV uczoE< cozomtt

Day of Year

Irrigation amounts applied to treatments.

Figure 5.3.

The

(GFD)

region between vertical dashed lines represents the period

when no water was applied to grain filling deficit

treatments.

158

corresponded to 1055 °Cd and 1273 °Cd for the first planting
date and to 991 °Cd and 1209 °Cd for the second planting date.

Four sample plants per plot were selected for
nondestructive measurements one month after planting. Leaf
area was determined two or three times weekly beginning with
the fourth leaf. Leaf length, taken as the distance from the
uppermost leaf ligule to the tip of a growing leaf, was
multiplied by the maximum exposed leaf width, and 75 96 of this
product was assumed to approximate the area of an individual
leaf (see Johnson and Tanner, 1972a: Linvill et al., 1978).
Leaf area was considered maximum when its respective leaf
ligule appeared. Silking was determined on ten random plants
every two or three days until it was complete. Silking was
declared for a respective plant when any silks were visible.

Biomass for the above ground portion of the plants was
determined several times during the growing season by a
combination of nondestructive estimates and destructive
sampling. Leaf and stem biomass (LFBIOM and STMBIOM) were
calculated from plant leaf area (PLA) and height to top leaf
ligule (LIG) for the period from DOY 166 to DOY 187 using the

following equations:

LFBIOM = 6.15 x 10*(PLA) - 2.83: :3 = 0.94 [1]

STMBIOM = 3.02 x 10*(LIG) + 0.89; r2 = 0.87 [2]

159
Leaf biomass was for visible blades and sheathes only. The
stem biomass included leaves which had not emerged from the
whorl of the plant, as well as internodes. Beginning DOY 195,
biomass was obtained by harvesting four plants per treatment
and oven drying them at 60 °C until no further weight loss
occurred (usually 4 to 5 days). Prior to drying individual
plants were separated into leaves (blade and sheath included),
stems, husks-silks-cobs, and grain on each sampling date.
Crop growth rate (CGR) and grain growth rate (GGR) were
calculated from the derivative of smooth fitted lines.
Nitrogen content of plants sampled on 31 July (DOY 212) was
determined by micro-Kjeldahl procedures for leaves, stems, and
ears. There was no appreciable grain on this date, so the
whole ear (husks, cob, silks) was aggregated. Nitrogen
content of grain only was determined for DOY 227, DOY 249, and
harvest (DOY 270) plant samples.

Grain filling was monitored by sampling single kernels
from two plants per sub-plot twice weekly. Husks were gently
pulled back on sample ears, and five individual kernels were
removed from the center portion using a small knife and were
placed in an envelope. After oven drying at 60 °C, weight was
determined for each grain individually. After each sampling,
ears were covered by the husks which were then held in place
with a rubber band. The same plants were used for all the
sampling dates. This procedure was similar to a method

described by Tollenaar and Daynard (1978b). They determined

160
that there was no significant effect of husk and kernel
removal on the dry matter accumulation of remaining kernels.

On 27 September twenty ears per plot were harvested, and
yield, grain number, and final grain weight were determined
for each one. Ears were placed in an oven for four days at
60‘TL After drying, grain was removed from each ear manually
and was weighed and counted. Grain size distribution was
determined for a sub-sample of ears. This was accomplished
by weighing individual kernels of an 80 cm3 (ca. 200 kernels)
sample from single ears. These kernels were categorized in
50 mg increments for three ears of each plot.

Soil water content was measured using the neutron
scattering technique. Sampling was in 0.25 m increments to
a depth of 1.5 m. There were two access tubes in the center
row of each sub-plot. Measurements began shortly after
planting and were taken one or two times weekly until near
physiological maturity of the crop. The water content during
the deficit period was plotted and a line fitted through the
data for each sampled depth. Water absorption rate was

determined from the slope of the fitted line.

RESULTS AND DISCUSSION

Table 5.1 gives dates and degree days of 50 % and 75 %
silking for the various treatments. There was a range of four

days among the planting dates and hybrids. ‘Water was withheld

161

Table 5.1. Day of year (DOY) and thermal time after planting
(°Cd) when 50 % and 75 % silking occurred for treatments.

 

 

Treatment 50 % Silking 75 % Silking
--DOY-- --°Cd-- --DOY-- --°Cd--
3540 I P1 205 882 207 917
3540 GFD P1 206 899 207 917
3540 GFD P2 208 869 209 881
3475 I P1 204 864 205 882
3475 GFD P1 205 882 206 899

3475 GFD P2 207 853 208 869

 

162
after DOY 217 which was 9 to 12 days after 50 % silking. All
treatments had reached 100 % silking by this date. The soil
profile was at a substantial water content when irrigation
ceased, so stress did not occur for several days.

Soil water content differences were not detected between
hybrids, therefore these data were averaged. Figures 5.4a and
5.4b and Figures 5.5a and 5.5b depict water absorption rate
for the GFD P1 and GFD P2, respectively, during the deficit
period. Water content of the irrigated treatment was
favorable throughout the experiment. water absorption was
occurring at all depths at the beginning of the deficit which
indicated roots were distributed throughout the 1.5 m soil
profile. A rather rapid decrease in water absorption from the
0.00 m to 0.25 m depth occurred around DOY 223 for deficit
plants of both planting dates. This was generally coupled
with increased water absorption rate at depths below 0.50 m.

Water absorption from the 1.5 m profile of GFD treatments
was sufficient to meet transpiration requirements of plants
until at least DOY 227 (Figure 5.6). This was near the time
when LAI of GFD plants began to decline rapidly due to
senescence (Figures 5.7a and 5.7b). If the LAI decline, leaf
rolling, and potential water absorption at depths below 1.5
m were considered, transpiration was probably maintained
longer. Other research by the current authors with corn on
this soil revealed that when water absorption rate in the 0.00

m to 0.25 m layer of soil reached values of 3.0 to

163

 

 

 

 

14
13; e—a 0.00 to 0.25 m

a, o +H0.25t00.50m
*5 3 1212-20500: 0.75m GFD P1
0: .— 11-
C -
.9 Z: "’-
27 9?
C) )5 8:
.8 ° 7-

U
< 6‘
1.") '2
3 I 5..
o E -
g o 4-
44r0 3-
8 E .1

o 2
0: v 1.

0‘ .1

1 U I I I I I I I I I U I I I I I I I I
215 2i3 221 224 227 230 233 236 239
Day of Year

Figure 5.4a. Water absorption rates at depths of 0.00 to
0.25 m, 0.25 to 0.50 m, and 0.50 to 0.75 m during the deficit

period for the grain filling deficit, first planting date
treatment.

164

 

 

14
1310—0 0.75 to 1.00 m
0 8 12-9—01.00t01.25m
"" " H1.25t01.50 m
[2 2 ,1; cram
c .
.9 :1 101
‘é'.’ 9'1
a >~ 81
.o 8 74
< 6‘
I.” '2
d) l 5_
...:
o E -
g o 4-
6"}: 3‘.
o 2..
a: 3 .
1-
o 1 *rT I I

 

 

 

' ' f" ' ' ' I ' T I I ' l
215 2i6 221 224 227 230 233 236 239

Day of Year

Figure 5.4b. Water absorption rates at depths of 0.75 to
1.00 m, 1.00 to 1.25 m, and 1.25 to 1.50 m during the deficit

period for the grain filling deficit, first planting date
treatment.

165

 

 

14'

13: 0-0 0.00t0 0.25m
a) O -e—aO.25t00.50m
44 O 12‘
O O ‘ H 0.50 to 0.75 m
0: ‘_ 11. GFDPZ
c .I
.9 :10‘
‘07 9?
C) )5 8'
ml (3 7:
D “o
< u
w) 5:
.9 I 51
o E *
3 o 4:
44:0 3-
8 E i

o 2

0: V 1.

0‘ .

 

 

 

"lr’l 'l"l"1"l"Trrl
215 218 221 224 227 230 233 236 239

Day of Year

Figure 5.5a. Water absorption rates at depths of 0.00 to
0.25 m, 0.25 to 0.50 m, and 0.50 to 0.75 m during the deficit
period for the grain filling deficit, second planting date
treatment.

166

 

 

 

 

 

14
1310-0 0.75 to 1.00 m
0 8 12- e—a 1.00 to 1.25 m
...: ..
O O . H 1.25t01.50 m
n: ... 11.. GFD P2
C d
.9 f: “’9
"é'.’ 9‘-
O >‘ 8‘
m (J 7;
D ‘o
< .
L."7 6:
8 ' 5«
o E J
g 0 4"
+JN) 3-
O .
0 E5 2.
CE 8, .
1‘
O W U I I I I 1 I I I I I U I I I j I ‘ I r I V I
215 218 221 224 227 230 233 236 239

Day of Year

Figure 5.5b. Water absorption rates at depths of 0.75 to
1.00 m, 1.00 to 1.25 m, and 1.25 to 1.50 m during the deficit

period for the grain filling deficit, second planting date
treatment.

167

 

 

 

 

 

10
A o—o Potential
'- 9- a—a Measured GFD P1
'>~ ‘ H Measured GFD P2
0 8‘
‘O .l
E 7‘
E 6-
” .
2 5'-
4..
g .
:5 I!)9
O .
6 2-
Q d
C!
> 1-
U .
0 "IT'I*‘IF'IT'I'*I'*I"1
215 218 221 224 227 230 233 236 239
Day of Year
Figure 5.6. Potential evaporation and measured total water

absorption from the 1.5 m soil profile during the deficit
period for the grain filling deficit treatments.

168

 

 

7.0‘ . .
. o—o 3540lP1 : :
A Ila—a 3540 GFD P1 : :
‘7' 50? H 3540 cm 92 A ; :
E f : .
N 5.01 :
‘ l
5 : g .
4404 ,
x < , . ,
Q) J l ‘¥~\\
'0 1 u u -.
£5 31}— : :
o : . .
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i . I l
: i v 1 l
0.0 ...,..fi,fl.—.4.-j4_,- .,

 

 

 

., r
150 170 190 2i0 230 250 270
Day of Year

Figure 5.7a. Leaf area index (LAI) for treatments of hybrid
3540. The region between the vertical dashed lines represent

the water deficit period, and the V marks silking date of
irrigated control.

169

 

 

 

 

7.0‘ . .
. 0-0 3475 1 P1 : :
A I H 3475 GFD P1 : :
(r 5-0‘. H 3475 cm P2 -: : :
«l '. -\
E : .:/ I :
CV 51}? ', :1
E : i i ‘
4.0- : .. .
x I u
g . : . u .
5 1°: : l 1'
° : : :
2 2.01 l l
‘ 1 l
I... : l l
3 10-1 : i
.1 ' . I l
: . - v i l
J . I I
000 - r T T I f I I—I I I I I I1 I I I #1 1'1 fi fi 1 I
1 {>0 1 70 190 21 0 230 250 270
Day of Year

Figure 5.7b. Leaf area index (LAI) for treatments of hybrid
3475. The region between the vertical dashed lines represent
the water deficit period, and the V marks silking date of
irrigated control.

170
3.5 (absorption units) plant extension growth essentially
ceased (NeSmith et al., 1990). The magnitude of the stress
in this experiment can be discerned as water absorption rate
in the upper soil layer was between values of 1.0 and 2.0
(absorption units) by the end of the deficit period.

Above ground biomass accumulation began to decline for
GFD plants as compared to I plants about the same time LAI
declined rapidly (Figures 5.8a and 5.8b). Hybrid 3540 had
more leaf area and greater biomass overall than hybrid 3475.
The reduction in biomass was more apparent from the crop
growth rate (CGR) calculations (Figures 5.9a and 5.9b).
Maximum CGR reductions of GFD plants were near DOY 231 as the
I plants were still growing substantially. The decrease in
CGR at this time was 63 96 to 67 % for all GFD treatments
except 3475 GFD P1 which only had a reduction of 46 %. The
corresponding decrease in LAI of deficit plants was 20 % to
25 % for P1 plants and 30 % for P2 plants, indicating that
leaf area loss could not account totally for reductions in
biomass production. This would seem to suggest an effect on
photosynthesis in the deficit plants.

Several previous reports have indicated that dry matter
accumulation ceased due to impairment of photosynthesis under
water deficit conditions during grain filling (Jurgens et al. ,
1978; McPherson and Boyer, 1977; Westgate and Boyer, 1985).
This compares the with work of Frey (1981) in which a 20 % to

30 % reduction in CGR was observed when 50 % defoliation was

171

)

 

. o 35flJIP1
300: a 3540 cm P1
270-3 a 3540 cm 92

    
  

---------d

  

.\_.-

P--o-—----

 

 

 

 

J r'

Y I I 1 j V T 1 j

150 170 190 210 230 250 270

T Y—YTjT T

Above Ground Biomass (gms plant
2'5
0
Ail

Day of Year

Figure 5.8a. Above ground biomass for treatments of hybrid
3540. The region between the vertical dashed lines represents

the water deficit period, and the V marks silking date of
irrigated control.

172

')

 

330
o 3475 1 P1

300-3 a 3475 GFD P1
2701 A 3475 GFD P2

   

 

 

 

0" I r II TTY‘ITIW IYI‘IT

1
150 170 190 2io 230 250 270

Above Ground Biomass (gms plant
Efi
A l A

Day of Year

Figure 5.8b. Above ground biomass for treatments of hybrid
3475. The region between the vertical dashed lines represents

the water deficit period, and the V’nmrks silking date of
irrigated control.

173

 

A

" 50 r
I) -o-o354OIP1 ;
O45 H35406FDP1 :
P H354OGFDP2 .

ca 40 E

‘ " 3"»: um—

b‘ 00
C3 (9
lLlllhlllllllLL‘llllll l

     

'- ------—--d

BO ha
C3 (fl

AlllllllLllllAlljllLllLA

..a
C3

 

 

_--_-----_---

 

 

Crop Growth Rate (gms m
a:

5
V
O I I 1 I I r I T I 1 I I I I—v—w
150 170 190 210 230 250 270
Day of Year
Figure 5.9a. Above ground crop growth rate (CGR) for

treatments of hybrid 3540. The region between the vertical
dashed lines represents the water deficit period, and the V
marks silking date of irrigated control.

174

 

‘/\.
" 50 I
l 3 0—0 scusup1 :
5‘ 455-: H 3475 GFD P1 ;
'0 H 3475 GFD P2 1
(V 40 :
I
I

    

’-------—’-.--d

 

 

 

Crop Growth Rate (gms m
5?

o . T . ,
150 170 150 210 2:50 250 270
Day of Year
Figure 5.9b.* Above ground crop growth rate (CGR) for

treatments of hybrid 3475. The region between the vertical

dashed lines represents the water deficit period, and the V
marks silking date of irrigated control.

175
performed on plants at mid-silking. Recovery of deficit
plants in the current experiment after irrigation resumed was
difficult to determine because: I jplants had started to
decrease CGR sharply due to approaching maturity.

The influence of the water deficit was less pronounced
for grain dry matter accumulation, although, marked
differences occurred (Figures 5.10a and 5.10b). Examination
of grain growth rates (GGR) indicated that maximum reductions
of GFD plants as compared to I plants occurred around DOY 235
and were 27 % to 29 % for all treatments except 3475 GFD P2
which was decreased by over 50 % (Figures 5.11a and 5.11b).
These data indicated that translocation of stored assimilates
was less influenced by the water deficits than was current
assimilation. This agrees with results of McPherson and Boyer
(1977) and Westgate and Boyer (1985).

Nitrogen content of plants after silking and of grain on
three subsequent dates is given in Table 5.2. Data were
somewhat variable, but there was no discernable effect of
treatments on the percent of nitrogen in the grain. This
would support the hypothesis of continued translocation under
deficit conditions. Research has shown that nearly all grain
nitrogen is that which is accumulated prior to anthesis and
that deprivation of nitrogen during grain filling has little
effect on grain nitrogen content (Friedrich et al., 1979;
Friedrich and Schrader, 1979; Hanway, 1962). Therefore, even

though drying of the surface soil layer during the water

176

 

 
   

 

 

140 O p540| PI '
.1“ a 9540 cm P1 E ,,,,,
I“ . a 6540 cm P2 1
c 120‘ : : ’§’
0 I I I
a 1 : x
m 100- : . ,'
E i 1 i
3 so; i E
q, 2 i
I
‘6’ 60- g
E I I
O . '
a 40‘ : I
‘ I I
C ‘ I I
'- ‘ I I
3 2°: : :
I I l
cfi—IIIIIIIII'IIWiIIIIIfiIIIIIIIIIIIIIII
2‘ o 220 230 240 250 260 270 280

 

Day of Year

Figure 5.10a. Grain biomass for treatments of hybrid 3540.
The region between the vertical dashed lines represents the
water deficit period.

177

 

     

 

 

A 140: O F5475 I PI :
.- j n 9475611) P1 1 ....... I
I . A 6475 cm P2 I ’ ....
E 120‘ : : ’1’ ¥
2 : I I 1’
a 1001 : I
m . : L
J
S, 1 : I".
V 80‘i I I
. I I I
3’, i I ”we”
a 60- g , r’
E I I ,z”
o ‘ I /
E5 401 I
c . I
.- . .
g 20': :
d I
4 I
O 1‘VTg‘jtT—TTUYFTIUT'ITVYTwrrTT‘I'TY‘IV

 

21 O 220 230 240 250 260 270 280
Day of Year

Figure 5.10b. Grain biomass for treatments of hybrid 3475.

The region between the vertical dashed lines represents the
water deficit period.

178

 

 

 

 

 

'- 50. . T
'>. ”455401191 ;
a 45-Ea-aps4ocrop1 :
‘3 40;I.-.'e,.54oc;1=131=>2 :
N 1
I 1 I I
E 35-3 I I
1 I I
330-; I .
3 3 I :
251 I 1
.9 a i '
(g 201 I I
I I I
1: 15a: : :
E; j I I
a 10-3 I I
L 4 I I
o 53 I I
.5, : :
I. 0 I..‘.,11a.ITrHI.T..l.n.,.fT.1r.Tr
0 210 220 230 240 250 260 270 280

Day of Year

Figure 5.11an Whole jplant. grain. growth rate (GGR) for
treatments of hybrid 3540. The region between the vertical
dashed lines represents the water deficit period.

 

179

 

I) :o-OISUSIPI
O 451 H IG475 GFD PI
" :stcmpz

--_--d

 

N
O
h

 

 

 

0 fTYIUUUVT—Vrj‘IW'TT'Y—Y'V‘UjYV Uri?

210 220 230 240 250 260 270 280

Groin Growth Rate (gms m

Day of Year

Figure 5.11b. Whole plant grain growth rate (GGR) for
treatments of hybrid 3475. The region between the vertical
dashed lines represents the water deficit period.

180

Table 5.2. Nitrogen content of whole plants excluding roots
on July 31 (DOY 212) and of grain only on August 15 (DOY 227),
September 6 (DOY 249), and September 27 (DOY 270).

 

 

Whole
Plant Grain
Treatment DOY 212 DOY 227 DOY 249 DOY 270
*
3540 I P1 1.41 (.03) 1.70 (.08) 1.39 (.07) 1.39 (.04)

3540 GFD P1 1.23 (.02) 1.76 (.04) 1.47 (.08) 1.40 (.05)
3540 GFD P2 1.29 (.08) 1.81 (.07) 1.35 (.05) 1.41 (.01)
3475 I P1 1.25 (.07) 1.72 (.09) 1.23 (.03) 1.35 (.04)
3475 GFD Pl 1.28 (.06) 1.59 (.02) 1.31 (.07) 1.28 (.02)

3475 GFD P2 1.32 (.09) 1.92 (.04) 1.40 (.02)

...}

.39 (.03)

 

* Values in parenthesis () are standard errors of treatment
means where n = 4.

181
shortage could have potentially influenced nutrient uptake,
this would not have necessarily reduced transport of nitrogen
to the grain.

A comparison to determine simplistically to what extent
translocation contributed to grain filling in the different
hybrids and treatments is through the ratio of CGR to GGR
(Figures 5.12a and 5.12b). The days represented were during
the linear grain filling period. A value greater than one
(CGR. > GGR) indicates that. photosynthesis exceeded that
required by the growing grain, and a value less than one (CGR
< GGR) indicates that current assimilation did not meet the
grain growth requirement. This ratio does not consider root
growth or plant respiration. All GFD plants had ratios less
than one, but there was little difference between hybrids in
response to the deficit. These results compare with those of
Jurgens et al. (1978) which indicated that a terminal water
deficit during grain filling resulted in grain accumulating
2.7 times as much dry matter as the entire shoot. Irrigated
plants of the hybrids in the current study were different in
that hybrid 3540 maintained a higher ratio than hybrid 3475.
The significance of this is difficult to determine since
yields (presented later) were not different for the irrigated
hybrids. However, this suggests that this ratio, or some
modification, might be useful in selecting hybrids in a

breeding program.

182

 

.9

H

O

a:

3 :3 35401121
0 a 3540 cm P
0‘ 2221 3540 cm
L

...:

3

O

I.

o

.S

O

I...

o

0

a

O

o:

I:

...:

3

O

L.

O 0 0

8. ° Day 226 Day 234 Day 242
5

Figure 5.12a. Crop growth rate (CGR) to grain growth rate

(GGR) ratios for treatments of hybrid 3540 during linear grain
filling.

183

 

.9

4.1

O

a:

3 1:: 34751 P1
0 E 3475 cm P
0‘ :22! 3475 GFD
.5

+4

3

O

I.

o

.E

O

L.

o

(D

+0

0

0:

.C

4.:

3

O

L

o 00

8. ' Day 226 Day 234 Day 242
5

Figure 5.12b. Crop growth rate (CGR) to grain growth rate
(GGR) ratios for treatments of hybrid 3475 during linear grain
filling.

184

The grain growth results presented thus far have been
for the entire plant. While these data are useful in some
analyses, it is difficult to determine effects on rate and
duration of grain filling from them. Figures 5.13a and 5.13b
represent weight of individual kernels for the various
treatments, and Figures 5.14a and 5.14b depict the rate of
filling. For simplification, a linear extrapolation to zero
grain filling was made. While this did not give the exact
date of beginning grain fill because of the absence of the
lag period, it did permit estimates of duration differences
between treatments.

Water deficits did not affect the rate of linear grain
filling of hybrid 3540, but it did decrease the duration by
7 to 8 days. As for hybrid 3475, rate was decreased by 14 %
and 24 % for GFD P1 and GFD P2, respectively, and duration
was decreased by 4 days and 2 days, respectively. These
differences were apparently genetically related, as attempts
to correlate rate or duration with developmental patterns
(e.g. day of silking) were not successful. Also, there was
no correlation with LAI or CGR. Mixed results of stress due
to defoliation on grain filling rate and duration have been
found. Tollenaar and Daynard (1978c) reported rate and
duration were both affected, but there were little hybrid
differences. Frey (1981) observed no influence on rate of

filling for kernels in the middle position of the ear, and

185

 

    
 

 

 

350 . .
I o :35401P1 :
A : o psmcro P1 ;
T 300‘. A .0540 cm P2 :
U 3 ' ' -
I” 250- I I ’ “H
v -1 I I
"’ 2 I :
‘5” 200-; I E
“’ j I 1
‘ I I
1%, 150‘: I I
.6 :1 : I
3 100-: I II
.E . I I
O 2 I I
5 50-: I I
a E E
a ..L. W” 4.1.,sf.4,....,..1r ...
210 220 230 240 250 260 270 280

 

Day of Year

Figure 5.13a. Single kernel weights for treatments of hybrid
3540. Samples were from the middle of the ear. The region

between the vertical dashed lines represents the water deficit
period.

186

 

   
 

 

350 I I
o 5475 1 P1 :
A . a 0475 GFD P1 I
.- 300‘. A 0475 GFD P2 1 4,4
I . I I -
p ' ' : x’I
. I I
8 250‘. I I x '
m - I I
‘ I I
C” ‘ 1 I
E 200: : :
\’ ‘ 1 I
44 I I I
C 150- ' '
P . : I.
'6 l 1
3 100-' I
c I : :
'6 j 1 1
65 501 I E
‘ I
I , I
c 1 III III I I' I T7 I JV 7 I I Y Y 1 I Y I 7 I Y ‘ 1' I I Y Y T V
2‘ 0 22 230 240 250 260 270 280

 

 

Day of Year

Figure 5.13b. Single kernel weights for treatments of hybrid
3475. Samples were from the middle of the ear. The region

between the vertical dashed lines represents the water deficit
period.

187

 

 

 

 

 

A
P 10 j— T
I I I I
>~ I I
O 9- I I
U . I I
T 8‘ I I
‘ | I
3 u : ““f“’§“
0 I I I
I" 6- I I
°’ ‘ I I
E 5- : :
‘ I
8 4* 3 :
0 d | I
01 3_ I :
2’ ‘ ‘ I
= 2- I .
E ‘- I354OGFDP2 ”I
c 1“ — 3540mm I
'- ‘-- mm 1
e 0 VTYDrs‘fytttwvwi vrv YV‘fY’IVITIr—Vfiif
o

21 0 220 230 240 250 260 270 280
Day of Year

Figure 5.14a. Grain filling rate of single kernels for
treatments of hybrid 3540. Samples were from the middle of
the ear. The region between the vertical dashed lines

represents the water deficit period.

188

 

 

 

 

 

 

A
" 10 j I
I I I I
5‘ 9- I I
U i I I
T 8‘ I .......... I ------- I
p I I I
Q) 7‘ I I
Q) .I I :
m w I ----+_
g . : :
54 I I
v I I
‘ I I
3 4- I :
I2 ‘ . :
3‘ I I
2’ ‘ I I
E 2" I I
u: ‘- 3475sz I
c 1" —I347scroPI :
'5 0‘ -- p475IPI 1
L. YYYU‘IIYUV‘IYYW'VYITTTITITVYIVITTYT
O 210 220 230 240 250 260 270 280

Day of Year

Figure 5.14b. Grain filling rate of single kernels for
treatments of hybrid 3475. Samples were from the middle of
the ear: ‘The region. between 'the ‘vertical dashed lines

represents the water deficit period.

189
Jones and Simmons (1983) denoted rate reductions ranging from
20 % to 60 %.

Final grain yield and yield components for treatments
are depicted in Figures 5.15a and 5.15b. There was little
difference between yields of the hybrids in response to the
water deficits. Yield reductions for GFD P1 and GFD P2 plants
were 21 % to 23 96 and 35 96 to 40 %, respectively. These
results compared favorably to those reported for the field and
container grown experiments discussed earlier in this
manuscript. The yield component most reduced for GFD plants
overall was grain weight. Results of grain number were
variable, but generally P1 plants were less affected than P2
plants. This was due to P2 plants being nearer the critical
time for grain number determination when water was withheld.
Results from several experiments have indicated that stress
drastically reduced grain numbers up until beginning linear
grain fill, and after this, grain‘weight was the more affected
component (Claassen and Shaw, 1970; Egharevba et al., 1976;
Frey, 1981; Grant et al., 1989; Jones and Simmons, 1983:
Kiniry and Ritchie, 1985).

Generally, final grain size is determined by weighing a
large sample of seeds and then dividing by the count. This
does not expose effects on grain variability within a
treatment. Figures 5.16a through 5.16f depict grain size
distribution for all the treatments. Compared to irrigated

plants deficit plants in general had a larger number of seeds

190

300

c: 3540 I P1
275 E 3540 cm Pl
250 ESS 3540 GFD P2

225
200
l 75
1 50
l 25
I 00
75
50
25

Grain Weight (mg seed
Groin Yield (gms plant

 

550
500
450

350
300
250
200
1 50

3%

Yield Grain Wt. Grain No.

Figure 5.15a. Grain yields, final grain weight,
grain number per ear for treatments of hybrid 3540.

and final

Groin Number per Eor

191

 

300 600
E: 3475 l Pl
A 275 a 3475 GFD P1 55°
I-l- ..." 250 m 3475 cm P2 500
I
g g 225 450
III a 200 400
0’ In 175 350
E E
V m 150 300
...o V
‘5, E 125 250
'5 .9 200
g >_ 100
c E 75 150
g 3 so 100
25 50
O . . 0
Yield Gram Wt. Gram No.
Figure 5.15b. Grain yields, final grain weight, and final

grain number per ear for treatments of hybrid 3475.

Groin Number per Ear

192

50
45.. 3540 I Pl

 

W
40-1 %
35‘
30‘

25d

. '7 .
20- / '1'

 

 

Percentage of Grains per Ear

 

 

 

1:: //
:myo” "”7 3°°////5U °°

Grain Size Class (mg seed 00)

Figure 5.16a. Grain size distribution on single ears at
harvest for the hybrid 3540 I P1 treatment.

’50

 

 

 

é: , M

“a :2: WM

:3, 10- 7 717 %%V%%

°' :1... I

Grain Size Class (mg seed-

d

194

 

45q 3540 GFD P2

254 ' ”g/
7 /

1° 7/ " '/ //

-1
Grain Size Class (mg seed )

 

N
‘E’

 

Percentage of Grains per Ear

 

Figure 5.16c. Grain size distribution on single ears at
harvest for the hybrid 3540 GFD P2 treatment.

195

 

3475|P1

8133
1 1 1

7/

ca
‘3

 

d N N
U‘ C a!
l l l

 

 

\\\\\\\\\\\ %

(fl
1

 

\\\\\\\‘
\

OMMM”/%/M

100 150 200 250 3001350 400
Grain Size Class (mg seed- )

Figure 5.16d. Grain size distribution on single ears at
harvest for the hybrid 3475 I P1 treatment.

196

50
45.. 3475 GFD P1

 

4o«
35-- N g
30- I

25d_ 7/7/

 

l

:2? //
5 /%/A%//fl//

Percentage of Grains per Ear

 

 

7 %/

0 so 100 150 200 250 300 350 400
. . —1
Gram Size Class (mg seed )

 

Figure 5.16e. Grain size distribution on single ears at
harvest for the hybrid 3475 GFD Pl treatment.

8. 20 g //77/
g ‘0 g7 '/ ,7 1., %%%//

 

     
 
 
 
  
    

  

 

    

   

 

o 50 100 150 200 250 300 350 400
O O -1
Gram Size Class (mg seed )

198

weighing less than 100 mg and a smaller number in the range
weighing greater than 200 mg. Effects on GFD P2 plants were
more pronounced than on GFD P1 plants. The seeds less than
100 mg were smaller and less developed, and usually they were
near the tip of the ear and were not really mechanically
harvestable. If these were not considered, final grain
weights would not have been. as greatly different among
treatments, however, grain number would have been more so.
Claassen and Shaw (1970) also indicated grain size calculation
varied considerably depending on whether all grains or only
those more developed were regarded. The knowledge of which
grains are used in size determination is helpful in comparing
experiments and would be beneficial in using research work
for crop model validation.

In summary, results have shown that soil water deficits
during grain filling reduced green leaf area and crop and
grain growth substantially for two corn hybrids. The effect
on yield and yield components was dependent on how early in
the grain filling process the deficit occurred. The nearer
it was to the beginning of grain filling, the greater the
reductions in grain number and yield were. Later deficits
reduced primarily grain weight. Grain weight reductions were
generally caused by a shortened linear grain filling period,
although, one hybrid demonstrated a marked influence on rate
of filling as well. Grain number reductions were magnified

when less developed seeds (those less than 100 mg) were

L__.____ w..-.--n‘.n—_ .—_ .

199
accounted for through grain size distributions. These results
suggest it is critical in managing crop water supply through
irrigation to avoid water deficits from flowering until linear

grain filling so that maximum kernel number can be achieved.

LIST OF REFERENCES

Barnett, R.H. and R.B. Pearce. 1983. Source-sink ratio
alteration and its effects on physiological parameters in
maize. Crop Sci. 23: 294-299.

Claassen, M.M. and R.H. Shaw. 1970. Water deficit effects
on corn. II. Grain components. Agron. J. 62: 652-655.

Denmead, O.T., and R.H. Shaw. 1960. The effects of soil
moisture stress at different stages of growth on the
development and yield of corn. Agron. J. 52: 272-274.

Duncan, W.G. 1975. Maize. Q L.'I'. Evans (ed.) Crop
physiology; pp. 23-50. Cambridge University Press, New York,
New York.

Egharevba, P.N., R.D. Horrocks, and M.S. Zuber. 1976. Dry
matter accumulation in maize in response to defoliation.
Agron. J. 68: 40-43.

Foale, M.A., R. Davis, and D.R. Upchurch. 1986. The design
of rain shelters for field experimentation: A review. J.
Agric. Eng. Res. 34: 1-16.

Frey, N.M. 1981. Dry matter accumulation in kernels of
maize. Crop Sci. 21: 118-122.

Friedrich, J.W., L.E. Schrader, and E.V. Nordheim. 1979. N
deprivation in maize during grain-filling. I. Accumulation of
dry matter, nitrate—N, and sulfate-S. Agron. J. ‘71: 461-465.

Friedrich, J.W. and L.B. Schrader. 1979. N deprivation in
maize during grain-filling. II. Remobilization of 15 N and
35’S and the relationship between N and S accumulation. .Agron.
J. 71: 466-472.

Grant, R.F., B.S. Jackson, J.R. Kiniry, and G.F. Arkin. 1989.

Water deficit timing effects on yield components in maize.
Agron. J. 81: 61-65.

200

201

Hanway, J.J. 1962. Corn growth and composition in relation
to soil fertility: II. Uptake of N, P, and K and their
distribution in different plant parts during the growing
season. Agron. J. 54: 217-222.

Hanway, J.J. 1969. Defoliation effects on different corn
(Le; a s, L.) hybrids as influenced by plant population and
stage of development. Agron. J. 61: 534-538.

Johnson, D.R. and J.W. Tanner. 1972a. Comparison of corn
(Zea mays L.) inbreds and hybrids grown at equal leaf area
index, light penetration, and population. Crop Sci. 12: 482-
485.

Johnson, D.R. and J.W. Tanner. 1972b. Calculation of the
rate and duration of grain filling in corn (Zea mays L.).
Crop Sci. 12: 485-486.

Jones, R.J. and S.R. Simmons. 1983. Effect of altered
source-sink ratio on growth of maize kernels. Crop Sci. 23:
129-134.

Jurgens, S.R., R.R. Johnson, and J.S. Boyer. 1978. Dry
matter production and translocation in maize subjected to
drought during grain fill. Agron. J. 70: 678-682.

Kiniry, J.R, and. J.T. Ritchie. 1985. Shade-sensitive
interval of kernel number of maize. Agron. J. 77: 711-715.

Linvill, D.E., R.F. Dale, and H.F. Hodges. 1978. Solar
radiation weighting for weather and corn growth models.
Agron. J. 70: 257-263.

Martin, E.C., J.T. Ritchie, S.M. Reese, T.L. Loudon, and B.
Knezek. 1988. A large-area, light-weight rainshelter with
programmable control. Trans. Am. Soc. Agric. Eng; 31: 1440-
1444.

McPherson, H.G. and J.S. Boyer. 1977. Regulation of grain
yield by photosynthesis in maize subjected to a water
deficiency. Agron. J. 69: 714-718.

NeSmith, D.S., A. Miller, and J.T. Ritchie. 1990. An
irrigation system for plots under a rain shelter. Agric.
Water Management. (In press).

NeSmith, D.S., J.T. Ritchie, and A.J.M. Smucker. 1990. Pre-
anthesis soil water deficit effect on corn (Zea mays L.). I.
Vegetative growth and development. (In review).

202

Robins, J.S. and C.E. Domingo. 1953. Some effects of severe
soil moisture deficits at specific growth stages in corn.
Agron. J. 45: 618-621.

Tollenaar, M. 1977. Sink-source relationships during
reproductive development in maize. A review. Maydica XXII:
49-75.

Tollenaar, M. and T.B. Daynard. 1978a. Kernel growth and
development at two positions on the ear of maize (Zea mays).
Can. J. Plant Sci. 58: 189-197.

Tollenaar, M. and T.B. Daynard. 1978b. Dry weight, soluble
sugar content, and starch content of maize kernels during the
early postsilking period. Can. J. Plant Sci. 58: 199-206.

Tollenaar, M. and T.B. Daynard. 1978c. Effect of defoliation
on kernel development in maize. Can. J. Plant Sci. 58: 207-
212.

Upchurch, D.P., J.T. Ritchie, and M.A. Foale. 1983. Design
of a large dual-structure rainout shelter; Agron. J. 75: 845-
848.

Westgate, M.E. and J.S. Boyer. 1985. Carbohydrate reserves
and reproductive development at low leaf water potentials in
maize. Crop Sci. 25: 762-769.

SUMMARY AND CONCLUSIONS

Results from these experiments have shown that potential
reductions in the use of water on irrigated.corn are dependent
on the growth stage of the crop. Periods of 18 to 21 days
without water on a sandy soil caused yield losses of 15 % to
25 % when the deficit occurred during pre-anthesis, as great
as 90 % when the deficit occurred during anthesis, and 25 %
to 40 % when the deficit occurred during the grain filling
period. These yield reductions indicate that pre-anthesis is
the stage when modifications in the use of water are the most
feasible, however, water deficit periods of duration similar
to that in these experiments are not recommended as yield loss
was too great at any growth stage.

Water deficits during pre-anthesis growth reduced plant
extension growth substantially, resulting in reduced plant
size including leaf area. A correlation between extension
growth and water absorption from the upper 0.25 m of soil was
observed. Further investigations would be helpful in
identifying reasons for this correlation. Some evidence
indicated nitrogen uptake hinderance under deficit conditions

could be linked to the extension growth reductions, yet the

203

204

data were limited and inconclusive. 2Research.is needed in the
area of nutrient uptake under field water deficit conditions.
Also, literature suggests that hormonal signals derived from
the root system in response to soil drying exist which
regulate above ground plant growth. The current experiments
did not prove or disprove such signals, however, the
correlation with surface soil drying, where roots are highly
concentrated, and reductions in plant extension growth lend
support to the concept.

The time period from just before anthesis until linear
grain filling was identified as being the most crucial to
obtaining maximum kernel number. Achieving a substantial
number of kernels to be filled was necessary in securing high
yields as compensation in grain weight was minimal for water
deficit plants which had reduced grain numbers. Timely
emergence of tassels and silks appeared to be necessary in
obtaining adequate pollination. Additionally, ear extension
growth was identified to occur over a finite period of time,
and interruption of this process was detrimental to yields.

The linear grain filling period was shortened.under'water
deficit conditions, and rate of grain filling was reduced for
one of the hybrids studied. These alterations in grain
filling caused.yield.losses through lower final grainwweights.
Examination of crop growth rate and grain growth rate in
response to water deficits during the grain filling period

showed the former was decreased more than the latter.

 

205

Apparently, translocation of assimilates was less affected by
water shortages than was production of assimilates. One
hybrid maintained a higher crop growth rate to grain growth
rate ratio longer than the other, however, this did not lead
to superior yields. No evaluation of root growth and
respiration was made for the grain filling water deficit
experiment, and this would be an area for focus of future
research in order to determine continuous whole plant carbon
balance during this growth stage.

Above ground biomass accumulation was highly dependent
on the production and maintenance of green leaf area.
Differences in crop growth rate under deficit conditions could
be attributed largely to less production or increased loss of
plant leaf area. Limited information on leaf rolling and
light interception demonstrated that these were important in
the observed alterations in crop growth rate of water deficit
plants. It was concluded that an assessment of the
"effective" leaf area under stress conditions is necessary in
interpreting biomass accumulation results. Research is needed
in this area, especially in order to decipher how to better
model the plant carbon balance under diverse environments.
Additionally, root growth data revealed increased partitioning
of carbon to roots of stressed plants, as rapid proliferation
at deeper depths occurred in response to a paucity of water.

Large, consistent differences in response to water

deficits between the hybrids used in this investigation did

206

not occur, especially in final yield. Most differences were
related to slightly different development of the cultivars.
Differences of 3 to 4 days in silking and beginning grain
filling are significant when plants are under deficit
conditions. It is important when comparing cultivar responses
to environmental conditions to insure that developmental
stages are not different" The.use of staggered.planting dates
to acquire similarly developing plants of different hybrids
appears to be useful in determining which observed plant
responses are genetic and which are developmentally derived.

Careful management of crops at specific growth stages
may offer the possibility of reducing applications of water
in more humid regions with acceptable yield losses. Periods
of water deficit less than 10 days may have little affect on
crop yields during certain growth stages, especially prior to
anthesis. Irrigation strategies which allow short periods of
water deficits, or that apply smaller quantities of water at
each application, appear to be those that will be successful
in reducing water use and maintaining production. These
strategies need to be optimized through computer analysis to

determine the risks involved so that management decisions can

be made.

APPENDICES

Appendix 1. Weather data for the 1987 growing season at the
Kellogg Biological Station.

 

 

207

Air High Air Low Air Mean Solar
Day of Temp. Temp. Temp. Radiation

Year Mo. Day (°C) (°C) (°C) (MJ m'z)
133 May 13 24.5 1.3 14.1 29.6
134 May 14 28.1 13.8 19.6 14.1
135 May 15 21.9 6.2 14.4 29.5
136 May 16 25.6 5.7 15.8 28.5
137 May 17 29.3 12.1 21.3 28.4
138 May 1 22.6 10.9 16.6 5.3
139 May 19 18.3 10.8 14.1 10.0
140 May 20 27.6 14.7 19.3 16.8
141 May 21 30.9 18.5 23.3 24.0
142 May 22 25.2 12.8 19.5 23.9
143 May 23 14.5 6.2 11.6 11.8
144 May 24 17.8 4.6 11.2 11.6
145 May 25 22.9 8.4 14.9 16.1
146 May 26 29.5 15.2 21.7 24.4
147 May 27 31.2 18.1 24.6 26.2
148 May 28 31.4 19.7 25.4 28.0
149 May 29 31.7 19.5 25.8 28.1
150 May 30 31.2 18.3 24.0 20.0
151 May 31 29.6 18.3 23.3 26.1
152 June 1 26.9 16.5 21.3 18.9
153 June 2 28.1 18.7 21.8 15.7
154 June 3 25.5 16.5 20.8 30.3
155 June 4 22.0 9.4 15.9 31.1
156 June 5 27.0 7.7 18.2 29.9
157 June 6 28.3 11.4 19.4 16.4
158 June 7 30.8 17.3 24.2 25.5
159 June 8 26.9 17.0 23.2 17.0
160 June 9 22.6 10.0 16.6 31.1
161 June 10 25.6 5.9 15.9 26.8
162 June 11 28.7 12.5 19.4 18.5
163 June 12 30.7 19.2 23.7 21.8
164 June 13 31.9 16.0 24.0 28.9
165 June 14 35.5 16.6 26.3 29.7
166 June 15 33.7 18.4 25.4 30.7
167 June 16 34.5 12.5 24.2 30.6
168 June 17 34.8 16.5 25.6 28.8
169 June 18 36.7 15.6 25.9 28.9

208

Appendix 1 (cont.)

 

 

Air High Air Low Air Mean Solar

Day of Temp. Temp. Temp. Radiation
Year Mo. Day (°C) (°C) (°C) (MJ m")
170 June 19 37.1 15.7 26.0 23.3
171 June 20 29.0 20.7 22.1 5.3
172 June 21 27.3 20.5 22.3 13.1
173 June 22 23.1 17.5 20.3 8.9
174 June 23 30.9 16.3 23.1 27.6
175 June 24 31.3 16.8 23.4 24.8
176 June 25 30.1 17.9 22.1 18.9
177 June 26 23.8 15.0 19.5 27.1
178 June 27 21.0 13.8 17.0 22.2
179 June 28 26.6 12.1 19.5 25.4
180 June 29 27.3 16.1 21.3 15.1
181 June 30 23.9 18.1 20.3 13.2
182 July 1 23.5 14.6 18.4 9.5
183 July 2 29.1 15.0 21.0 24.5
184 July 3 28.4 17.2 22.5 26.5
185 July 4 28.5 12.0 20.0 26.1
186 July 5 25.0 14.1 18.7 10.0
187 July 6 28.0 18.0 22.0 12.7
188 July 7 30.8 18.6 24.1 24.2
189 July 8 31.4 20.5 25.3 21.6
190 July 9 31.9 19.0 24.8 18.8
191 July 10 31.3 20.6 25.0 18.3
192 July 11 31.3 19.9 25.8 22.6
193 July 12 32.4 22.0 26.0 23.8
194 July 13 28.3 17.4 21.7 14.3
195 July 14 22.5 10.3 16.5 25.0
196 July 15 15.3 8.2 11.7 4.9
197 July 16 27.1 11.3 18.4 27.2
198 July 17 28.8 12.5 21.3 26.0
199 July 18 31.3 17.9 24.7 25.8
200 July 19 31.7 19.9 26.0 22.3
201 July 20 34.0 19.1 27.0 23.7
202 July 21 30.9 18.9 24.3 26.5
203 July 22 32.5 19.1 25.5 23.7
204 July 23 32.2 20.0 25.7 20.0
205 July 24 32.0 21.7 26.4 20.9
206 July 25 32.2 21.4 26.0 24.8
. 207 July 26 29.1 18.4 23.6 20.9
208 July 27 30.6 13.5 21.0 22.2
209 July 28 27.2 12.1 20.0 16.4
210 July 29 30.8 13.4 20.6 19.0
211 July 30 32.3 16.5 23.7 22.5
212 July 31 33.1 18.5 25.0 23.8
213 Aug. 1 32.3 21.2 25.0 15.9
214 Aug. 2 32.4 22.9 26.8 21.6

209

Appendix 1 (cont.)

 

 

Air High Air Low Air Mean Solar
Day of Temp. Temp. Temp. Radiation

Year Mo. Day (°C) (°C) (°C) (MJ m'z)
215 Aug. 3 34.1 18.3 26.1 26.0
216 Aug. 4 29.8 18.3 23.9 20.1
217 Aug. 5 28.0 13.9 20.0 19.8
218 Aug. 6 28.8 12.9 20.6 25.1
219 Aug. 7 30.6 15.2 22.7 24.0
220 Aug. 8 21.4 18.0 19.5 4.7
221 Aug. 9 28.2 18.5 22.0 15.1
222 Aug. 10 27.8 16.8 20.7 17.1
223 Aug. 11 30.0 13.5 21.1 24.4
224 Aug. 12 30.6 13.9 21.7 21.2
225 Aug. 13 31.2 15.0 23.2 21.3
226 Aug. 14 27.2 21.0 23.6 6.7
227 Aug. 15 31.9 22.8 26.5 20.3
228 Aug. 16 30.5 18.9 24.3 13.0
229 Aug. 17 28.6 17.7 24.2 24.1
230 Aug. 18 25.8 13.5 18.2 14.0
231 Aug. 19 24.8 13.1 19.0 24.2
232 Aug. 20 28.0 11.5 19.1 23.0
233 Aug. 21 28.8 17.3 22.4 18.9
234 Aug. 22 24.1 12.6 20.9 17.9
235 Aug. 23 20.9 10.1 15.3 20.4
236 Aug. 24 21.9 8.3 14.4 23.6
237 Aug. 25 20.1 8.2 13.7 12.3
238 Aug. 26 15.2 12.3 13.6 1.5
239 Aug. 27 15.6 13.6 14.6 2.6
240 Aug. 28 17.9 13.4 15.1 5.7
241 Aug. 29 23.2 9.3 16.5 22.4
242 Aug. 30 26.5 12.9 19.2 19.1
243 Aug. 31 20.7 8.5 15.6 20.7
244 Sept. 1 21.1 8.5 15.0 21.3
245 Sept. 2 21.5 11.1 15.4 20.2
246 Sept. 3 23.9 6.2 14.6 21.6
247 Sept. 4 27.0 7.3 16.7 22.1
248 Sept. 5 29.4 10.0 19.4 18.5
249 Sept. 6 28.3 14.9 21.3 18.9
250 Sept. 7 29.4 15.6 21.9 16.4
251 Sept. 8 22.7 15.7 18.6 6.0
252 Sept. 9 25.3 13.6 18.6 19.7
253 Sept. 10 27.9 11.6 18.9 18.2
254 Sept. 11 26.4 15.9 19.8 17.2
255 Sept. 12 25.8 13.9 18.7 18.5
256 Sept. 13 21.4 9.9 15.4 15.0
257 Sept. 14 24.9 6.3 14.7 21.0
258 Sept. 15 24.6 11.2 16.7 11.2
259 Sept. 16 21.6 16.0 18.3 4.8

260 Sept. 17 24.7 17.1 18.8 8.2

210

Appendix 1 (cont.)

 

 

Air High Air Low Air Mean Solar
Day of Temp. Temp. Temp. Radiation

Year Mo. Day (°C) (°C) (°C) (MJ m'z)
261 Sept. 18 17.6 15.1 16.4 3.3
262 Sept. 19 21.6 12.4 16.7 18.2
263 Sept. 20 17.3 9.5 12.4 7.4
264 Sept. 21 15.4 10.4 12.0 6.9
265 Sept. 22 19.4 9.4 12.8 9.7
266 Sept. 23 21.1 8.9 14.9 16.4
267 Sept. 24 20.4 9.5 14.9 17.4
268 Sept. 25 18.6 2.6 10.4 18.8
269 Sept. 26 24.4 7.7 15.0 17.6
270 Sept. 27 27.2 11.5 18.7 14.0
271 Sept. 28 26.6 12.7 18.8 13.4
272 Sept. 29 21.2 12.5 16.4 10.6
273 Sept. 30 17.0 6.8 11.8 12.2
274 Oct. 1 17.7 1.0 9.9 14.7
275 Oct. 2 14.7 4.2 9.1 7.0
276 Oct. 3 10.3 1.5 5.0 13.8
277 Oct. 4 17.1 -0.2 8.4 16.1
278 Oct. 5 16.8 6.9 11.0 9.5
279 Oct. 6 10.5 4.0 8.8 4.6
280 Oct. 7 7.6 2.6 5.1 5.2
281 Oct. 8 11.6 0.3 4.7 9.1
282 Oct. 9 14.8 4.3 9.2 11.7
283 Oct. 10 9.6 2.9 5.7 5.8
284 Oct. 11 9.4 -0.9 4.4 7.4
285 Oct. 12 12.5 -3.1 3.6 10.8
286 Oct. 13 15.6 -3.8 5.3 14.4
287 Oct. 14 18.4 3.1 9.7 11.0
288 Oct. 15 21.3 7.4 13.0 12.4
289 Oct. 16 21.2 3.6 12.3 10.9
290 Oct. 17 15.1 8.4 10.2 3.1
291 Oct. 18 18.0 5.8 10.8 13.4
292 Oct. 19 13.1 4.5 7.8 4.7
293 Oct. 20 9.5 2.4 5.4 6.8
294 Oct. 21 4.8 0.3 2.5 3.2
295 Oct. 22 5.5 0.2 2.6 1.5
296 Oct. 23 11.0 -0.3 5.4 11.8
297 Oct. 24 5.4 -l.7 2.2 2.1
298 Oct. 25 12.6 -4.2 3.0 13.1
299 Oct. 26 11.9 -2.6 4.3 9.1
300 Oct. 27 11.0 1.6 6.5 10.6

Appendix 2

. Weather data for the 1988 growing season at the

Kellogg Biological Station.

 

 

Air High Air Low Air Mean Solar
Day of Temp. Temp. Temp. Radiation

Year Mo. Day (°C) (°C) (°C) (MJ m'z)
112 April 21 9.78 -3.92 2.93 21.27
113 April 22 15.71 0.33 7.30 22.95
114 April 23 14.97 1.84 5.60 6.97
115 April 24 10.98 1.58 5.18 20.57
116 April 25 16.63 -3.41 7.93 23.79
117 April 26 16.95 5.34 10.90 16.47
118 April 27 10.25 2.50 4.53 4.56
119 April 28 13.60 2.22 6.91 22.50
120 April 29 17.28 1.13 8.48 25.33
121 April 30 20.44 2.46 11.35 27.28
122 May 1 22.40 1.05 12.61 27.81
123 May 2 23.38 4.02 14.58 28.15
124 May 3 18.99 4.31 11.63 20.44
125 May 4 19.39 1.75 10.70 23.08
126 May 5 22.01 4.35 13.17 21.77
127 May 6 26.31 5.43 16.47 28.21
128 May 7 25.64 6.58 16.55 23.26
129 May 8 27.50 13.13 18.94 19.68
130 May 9 18.14 11.43 13.67 13.38
131 May 10 15.04 7.98 12.31 9.16
132 May 11 20.78 1.47 11.58 28.87
133 May 12 24.02 8.49 16.23 20.68
134 May 13 19.43 8.61 15.45 28.46
135 May 14 23.87 4.16 14.04 28.51
136 May 15 26.82 11.57 16.97 12.89
137 May 16 18.88 9.92 14.11 26.37
138 May 17 21.49 8.33 13.37 25.18
139 May 18 24.84 5.96 15.27 28.88
140 May 19 24.81 7.43 16.16 21.59
141 May 20 26.16 13.20 18.47 20.75
142 May 21 27.68 13.85 19.77 18.43
143 May 22 31.64 11.99 22.31 25.61
144 May 23 20.75 16.15 17.56 5.26
145 May 24 21.18 5.96 14.83 28.00
146 May 25 18.81 1.41 9.53 30.21
147 May 26 24.11 2.36 14.52 29.82
148 May 27 27.50 11.51 19.74 29.09

211

212

Appendix 2 (cont.)

 

 

Air High Air Low Air Mean Solar
Day of Temp. Temp. Temp. Radiation

Year Mo. Day (°C) (°C) (°C) (MJ m'z)
149 May 28 29.83 10.77 20.63 22.92
150 May 29 31.06 14.59 22.74 28.17
151 May 30 31.58 12.31 22.56 27.83
152 May 31 34.03 12.50 22.77 28.83
153 June 1 32.45 14.55 23.69 27.96
154 June 2 20.42 9.38 13.25 11.31
155 June 3 22.26 5.77 13.73 28.89
156 June 4 24.42 4.44 15.22 30.32
157 June 5 29.28 10.80 20.35 28.94
158 June 6 31.70 16.33 23.51 28.89
159 June 7 31.77 16.07 23.87 29.53
160 June 8 24.58 7.74 16.29 26.63
161 June 9 20.65 4.00 12.11 30.21
162 June 10 22.73 4.35 14.22 30.52
163 June 11 26.68 4.54 17.00 29.17
164 June 12 30.33 11.08 21.81 30.15
165 June 13 33.45 15.02 24.25 29.27
166 June 14 34.12 19.18 26.48 27.69
167 June 15 32.41 20.28 25.56 26.72
168 June 16 29.46 14.55 21.18 26.55
169 June 17 30.33 11.62 20.66 25.42
170 June 18 32.93 11.10 22.27 30.30
171 June 19 32.65 17.76 25.13 25.96
172 June 20 32.85 19.57 25.75 24.73
173 June 21 35.85 16.06 26.22 27.23
174 June 22 33.67 21.18 26.64 15.19
175 June 23 29.28 13.21 21.42 30.77
176 June 24 29.16 13.70 21.63 24.97
177 June 25 35.82 22.04 28.29 27.62
178 June 26 25.89 13.18 18.65 24.30
179 June 27 29.06 10.08 19.15 29.85
180 June 28 24.13 12.49 16.82 8.47
181 June 29 25.27 11.06 18.02 31.46
182 June 30 25.37 7.38 17.06 28.69
183 July 1 25.63 6.82 17.12 26.93
184 July 2 28.99 7.57 18.69 29.28
185 July 3 31.82 7.82 20.78 28.75
186 July 4 34.62 10.71 23.71 28.36
187 July 5 37.74 14.43 26.37 26.23
188 July 6 38.58 15.89 27.27 25.73
189 July 7 37.89 17.65 27.46 21.88
190 July 8 35.65 18.75 27.04 25.09
191 July 9 35.09 17.21 26.53 24.07
192 July 10 29.01 20.08 22.71 12.54
193 July 11 29.73 17.12 22.93 26.57
194 July 12 30.43 11.67 21.47 26.91

Appendix 2 (cont.)

213

 

 

Air High Air Low Air Mean Solar
Day of Temp. Temp. Temp. Radiation

Year Mo. Day (°C) (°C) (°C) (MJ m'z)
195 July 13 32.16 11.85 23.15 25.55
196 July 14 33.30 20.48 27.22 28.39
197 July 15 37.13 14.98 23.33 17.37
198 July 16 34.98 20.65 26.64 17.61
199 July 17 32.66 20.04 24.77 25.29
200 July 18 24.61 18.72 21.48 4.46
201 July 19 31.07 18.43 23.71 21.97
202 July 20 24.57 16.48 20.09 8.91
203 July 21 28.14 15.79 21.14 20.74
204 July 22 29.84 15.90 19.67 16.12
205 July 23 30.09 14.04 19.62 20.70
206 July 24 28.88 13.45 21.05 26.87
207 July 25 27.91 17.26 21.42 17.53
208 July 26 28.40 14.44 20.81 24.61
209 July 27 29.64 13.40 21.60 23.94
210 July 28 33.07 19.59 25.85 26.92
211 July 29 32.24 19.90 26.08 25.72
212 July 30 30.27 20.67 24.91 17.59
213 July 31 31.21 15.27 23.27 23.97
214 Aug. 1 36.76 20.63 28.07 25.94
215 Aug. 2 35.51 23.16 29.18 24.53
216 Aug. 3 35.94 22.17 27.55 19.66
217 Aug. 4 34.40 21.67 27.86 20.76
218 Aug. 5 31.77 21.26 24.53 10.39
219 Aug. 6 29.21 18.30 23.67 26.34
220 Aug. 7 32.56 15.58 23.92 26.74
221 Aug. 8 31.93 18.10 25.01 21.74
222 Aug. 9 28.84 21.62 24.34 11.17
223 Aug. 10 29.98 19.75 23.67 11.84
224 Aug. 11 30.81 19.57 24.71 19.39
225 Aug. 12 32.82 20.87 26.65 20.61
226 Aug. 13 31.90 22.35 26.66 20.50
227 Aug. 14 32.32 18.47 27.60 21.23
228 Aug. 15 31.43 18.78 24.79 24.46
229 Aug. 16 32.85 15.68 24.33 21.54
230 Aug. 17 34.03 22.83 28.69 23.76
231 Aug. 18 22.79 15.44 20.29 5.48
232 Aug. 19 23.05 14.73 17.98 7.51
233 Aug. 20 27.26 13.83 20.19 24.39
234 Aug. 21 27.51 12.16 19.18 23.71
235 Aug. 22 24.58 11.05 17.65 18.01
236 Aug. 23 25.02 14.31 18.44 13.20
237 Aug. 24 24.24 15.73 19.17 19.76
238 Aug. 25 23.53 15.00 18.81 22.98
239 Aug. 26 23.35 10.83 17.25 22.30
240 Aug. 27 20.96 9.14 14.32 6.09

214

Appendix 2 (cont.)

 

 

Air High Air Low Air Mean Solar
Day of Temp. Temp. Temp. Radiation

Year Mo. (°C) (°C) (°C) (MJ m'z)
241 Aug. 21.85 10.67 16.82 19.74
242 Aug. 21.77 6.08 14.16 22.57
243 Aug. 23.92 8.21 15.73 21.78
244 Aug. 26.58 11.35 18.44 21.86
245 Sept. 27.42 10.33 19.01 21.22
246 Sept. 27.92 12.64 20.66 14.76
247 Sept. 25.04 15.86 19.44 11.94
248 Sept. 22.77 13.72 16.71 11.97
249 Sept. 16.52 7.85 11.89 17.46
250 Sept. 18.30 3.51 10.48 18.02
251 Sept. 21.70 3.03 12.38 22.09
252 Sept. 23.39 8.78 15.89 19.48
253 Sept. 25.21 9.38 18.62 21.46
254 Sept. 26.36 7.33 16.39 17.90
255 Sept. 27.46 10.48 18.08 17.50
256 Sept. 26.03 17.16 20.47 10.00
257 Sept. 20.94 10.11 16.64 18.71
258 Sept. 23.94 8.69 15.35 20.63
259 Sept. 22.97 5.89 14.20 19.81
260 Sept. 24.30 7.44 15.58 13.50
261 Sept. 28.61 18.18 22.04 11.77
262 Sept. 25.73 17.48 19.74 6.08
263 Sept. 21.12 13.74 18.07 3.29
264 Sept. 14.32 11.77 12.96 2.43
265 Sept. 14.43 10.75 12.43 5.41
266 Sept. 19.49 10.58 14.59 4.84
267 Sept. 19.59 8.51 15.79 17.91
268 Sept. 21.70 4.85 12.16 17.24
269 Sept. 21.93 4.63 12.89 18.15
270 Sept. 23.33 6.83 14.49 16.45
271 Sept. 25.64 12.93 18.03 13.50
272 Sept. 15.96 10.10 12.63 6.70
273 Sept. 23.93 8.14 14.85 13.37
274 Sept. 24.79 11.36 17.44 8.72
275 Oct. 1 22.67 16.13 18.54 5.51
276 Oct. 2 17.20 7.59 12.49 7.42
277 Oct. 3 15.63 4.51 8.82 16.97
278 Oct. 4 10.47 3.97 6.73 10.05
279 Oct. 5 12.40 1.74 6.01 13.75
280 Oct. 6 13.15 -1.76 5.08 10.85
281 Oct. 7 13.98 -0.32 6.46 13.84
282 Oct. 8 16.81 5.91 9.91 10.92
283 Oct. 9 16.69 6.64 10.13 11.63
284 Oct. 10 16.65 6.16 10.92 10.44
285 Oct. 11 7.91 2.08 4.49 7.24

Appendix 3. Weather data for the 1989 growing season at the
Kellogg Biological Station.

 

 

Air High Air Low Air Mean Solar

Day of Temp. Temp. Temp. Radiation
Year Mo. Day (°C) (°C) (°C) (MJ m'z)
91 April 1 6.9 -3.0 2.1 17.2
92 April 2 11.1 5.1 6.8 6.7
93 April 3 10.3 5.4 7.5 5.4
94 April 4 16.8 4.3 9.5 19.0
95 April 5 5.1 0.8 3.7 4.6
96 April 6 9.5 -O.2 3.9 16.0
97 April 7 8.5 -2.4 2.5 15.7
98 April 8 9.4 -2.2 1.8 11.4
99 April 9 -o.7 -6.5 -3.4 11.0
100 April 10 0.8 -9.5 -3.9 13.8
101 April 11 7.8 -6.8 0.7 19.4
102 April 12 6.6 -1.0 2.4 9.2
103 April 13 9.9 -3.1 2.8 24.7
104 April 14 13.2 1.0 7.3 7.9
105 April 15 17.1 0.7 8.6 22.0
106 April 16 20.2 -1.0 10.2 23.4
107 April 17 16.4 3.2 10.8 8.8
108 April 18 8.0 -o.5 3.0 9.8
109 April 19 13.5 -0.9 5.5 25.3
110 April 20 19.4 0.7 9.9 20.9
111 April 21 18.3 6.0 10.3 16.6
112 April 22 16.4 5.4 9.7 16.2
113 April 23 16.7 -O.9 7.6 25.9
114 April 24 20.9 0.0 10.6 24.3
115 April 25 27.4 9.2 16.9 21.3
116 April 26 24.0 11.6 17.1 24.1
117 April 27 22.7 9.7 14.6 18.3
118 April 28 11.1 6.7 9.1 4.4
119 April 29 17.6 6.4 10.0 10.8
120 April 30 14.5 5.2 9.4 24.5
121 May 1 16.6 2.1 9.2 23.0
122 May 2 8.4 2.7 5.9 7.6
123 May 3 16.9 1.9 8.9 27.0
124 May 4 19.5 6.1 12.0 21.8
125 May 5 16.3 5.3 11.4 20.8
126 May 6 6.8 -2.3 2.4 12.3
127 May 7 8.6 -4.1 2.4 25.1

215

216

Appendix 3 (cont.)

 

 

Air High Air Low Air Mean Solar
Day of Temp. Temp. Temp. Radiation

Year Mo. Day (°C) (°C) (°C) (MJ mg)
128 May 8 16.5 -0.4 8.0 17.8
129 May 9 16.9 6.6 11.7 21.0
130 May 10 18.5 0.9 10.3 27.7
131 May 11 17.3 2.7 9.4 29.1
132 May 12 15.5 6.1 9.7 8.9
133 May 13 16.3 6.6 9.5 9.3
134 May 14 18.4 5.8 11.2 15.2
135 May 15 16.9 8.2 11.7 12.9
136 May 16 24.9 5.1 14.3 23.5
137 May 17 27.3 5.7 17.1 26.4
138 May 18 24.1 10.1 18.3 14.9
139 May 19 20.5 15.3 17.7 5.0
140 May 20 21.2 11.1 16.7 9.8
141 May 21 24.6 8.9 16.5 29.1
142 May 22 27.2 7.1 17.0 21.1
143 May 23 26.8 11.1 18.6 29.8
144 May 24 26.3 10.3 18.7 19.8
145 May 25 23.7 14.4 19.2 13.9
146 May 26 22.7 11.2 18.1 29.1
147 May 27 17.4 8.2 12.4 27.3
148 May 28 21.4 2.3 12.9 28.2
149 May 29 21.3 8.2 15.1 15.1
150 May 30 27.5 17.1 20.9 15.6
151 May 31 27.8 17.3 20.7 10.9
152 June 1 24.5 17.2 19.1 12.4
153 June 2 25.2 14.2 19.7 29.9
154 June 3 20.7 13.8 16.9 7.7
155 June 4 22.8 10.3 16.5 29.2
156 June 5 24.2 10.7 17.1 20.9
157 June 6 27.6 10.0 19.7 28.3
158 June 7 29.6 15.5 22.3 26.7
159 June 8 28.1 15.8 21.6 20.2
160 June 9 23.3 11.5 17.4 21.9
161 June 10 19.8 10.1 13.5 19.8
162 June 11 25.6 5.0 15.9 29.9
163 June 12 17.0 14.8 15.6 5.5
164 June 13 22.2 14.5 17.5 10.6
165 June 14 24.1 13.7 16.9 14.9
166 June 15 19.1 10.7 15.0 12.5
167 June 16 13.8 10.0 11.6 6.9
168 June 17 23.1 10.0 16.7 24.8
169 June 18 25.9 14.3 20.1 26.8
170 June 19 21.9 16.8 19.4 7.4
171 June 20 25.9 15.9 19.2 17.7
172 June 21 28.4 13.7 19.7 21.5
173 June 22 28.2 16.0 21.2 12.7

217

Appendix 3 (cont.)

 

 

Air High Air Low Air Mean Solar
Day of Temp. Temp. Temp. Radiation

Year Mo. Day (°C) (°C) (°C) (MJ m'z)
174 June 23 32.2 18.1 23.3 21.1
175 June 24 30.8 18.2 24.0 27.0
176 June 25 33.9 17.5 24.4 26.7
177 June 26 32.0 19.0 23.7 19.8
178 June 27 24.2 18.2 20.7 8.3
179 June 28 24.5 15.0 19.9 29.1
180 June 29 24.5 7.8 16.4 30.4
181 June 30 27.4 8.5 18.1 30.0
182 July 1 29.8 10.9 20.7 28.9
183 July 2 30.9 15.4 22.1 22.1
184 July 3 28.5 17.8 22.7 23.8
185 July 4 31.7 17.0 23.9 24.0
186 July 5 30.4 17.5 23.8 25.7
187 July 6 32.5 18.1 25.0 26.7
188 July 7 29.9 17.9 24.1 27.0
189 July 8 28.7 14.3 22.1 22.0
190 July 9 31.0 19.6 25.1 22.5
191 July 10 31.5 24.3 27.7 25.2
192 July 11 31.1 18.5 23.5 18.4
193 July 12 24.5 15.5 19.8 12.1
194 July 13 26.1 15.1 19.3 14.7
195 July 14 26.6 11.8 18.7 28.1
196 July 15 27.2 11.5 18.7 21.8
197 July 16 28.2 11.4 19.9 21.9
198 July 17 28.5 12.4 20.7 26.6
199 July 18 28.9 13.1 21.0 20.0
200 July 19 22.7 17.2 19.0 7.6
201 July 20 19.9 15.9 17.7 5.1
202 July 21 25.4 16.3 19.8 11.2
203 July 22 30.5 16.7 22.9 22.5
204 July 23 31.4 17.1 24.0 25.9
205 July 24 32.5 18.9 25.1 18.0
206 July 25 30.7 20.2 24.0 14.9
207 July 26 31.0 20.0 25.1 22.8
208 July 27 29.1 18.8 24.0 17.0
209 July 28 26.0 14.4 20.2 19.8
210 July 29 25.8 9.1 17.7 21.5
211 July 30 19.6 15.4 17.6 5.8
212 July 31 28.7 13.2 20.5 22.8
213 Aug. 1 29.8 14.5 22.0 23.5
214 Aug. 2 28.6 15.3 22.0 24.7
215 Aug. 3 31.6 17.4 24.6 21.3
216 Aug. 4 29.4 21.7 25.1 16.6
217 Aug. 5 29.3 18.7 23.9 24.1
218 Aug. 6 24.0 10.0 18.2 15.6
219 Aug. 7 19.8 7.7 12.7 23.3

218

Appendix 3 (cont.)

 

 

Air High Air Low Air Mean Solar
Day of Temp. Temp. Temp. Radiation

Year Mo. Day (°C) (°C) (°C) (MJ m'z)
220 Aug. 8 24.0 5.7 15.1 22.0
221 Aug. 9 26.0 11.0 18.5 20.8
222 Aug. 10 27.8 12.6 18.6 15.8
223 Aug. 11 29.4 12.4 19.9 18.2
224 Aug. 12 27.4 13.7 19.6 14.3
225 Aug. 13 27.6 13.4 20.3 22.0
226 Aug. 14 27.4 15.4 20.1 16.1
227 Aug. 15 25.6 15.9 19.9 15.4
228 Aug. 16 24.1 12.7 17.6 18.5
229 Aug. 17 27.2 10.6 18.6 24.3
230 Aug. 18 25.8 10.0 17.5 20.5
231 Aug. 19 27.5 10.2 18.4 21.5
232 Aug. 20 27.2 16.9 20.9 15.0
233 Aug. 21 28.0 17.1 22.0 24.0
234 Aug. 22 27.4 16.9 21.9 13.8
235 Aug. 23 22.7 17.3 20.5 9.7
236 Aug. 24 25.9 13.3 18.8 20.2
237 Aug. 25 27.0 9.2 17.7 21.9
238 Aug. 26 28.8 11.2 19.5 22.5
239 Aug. 27 29.8 16.4 21.9 17.5
240 Aug. 28 25.2 16.4 20.7 6.0
241 Aug. 29 26.4 19.8 22.2 8.0
242 Aug. 30 25.2 15.1 19.5 23.0
243 Aug. 31 27.0 12.5 19.5 17.1
244 Sept. 1 25.2 17.3 20.4 13.7
245 Sept. 2 23.9 9.9 16.7 20.0
246 Sept. 3 25.7 8.9 16.4 20.7
247 Sept. 4 24.1 10.0 16.9 19.0
248 Sept. 5 27.6 15.4 20.4 15.4
249 Sept. 6 23.7 18.1 20.7 5.2
250 Sept. 7 28.8 18.3 22.1 13.2
251 Sept. 8 29.0 19.8 22.2 9.8
252 Sept. 9 27.0 17.7 21.3 10.7
253 Sept. 10 23.7 13.3 17.7 14.3
254 Sept. 11 24.2 10.7 16.7 11.6
255 Sept. 12 20.6 11.3 15.6 19.6
256 Sept. 13 11.2 8.9 10.1 1.9
257 Sept. 14 12.4 8.7 10.7 2.4
258 Sept. 15 21.7 4.8 12.6 20.8
259 Sept. 16 14.1 8.8 11.7 3.7
260 Sept. 17 23.9 6.1 14.7 18.9
261 Sept. 18 25.1 6.4 15.1 19.0
262 Sept. 19 25.5 6.9 15.6 18.3
263 Sept. 20 26.1 7.5 15.8 17.3
264 Sept. 21 26.2 8.1 16.7 15.0
265 Sept. 22 23.6 9.3 18.3 8.7

219

Appendix 3 (cont.)

 

 

Air High Air Low Air Mean Solar
Day of Temp. Temp. Temp. Radiation

Year Mo. Day (°C) (°C) (°C) (MJ m’z)
266 Sept. 23 11.0 2.2 6.4 13.3
267 Sept. 24 16.9 -1.9 6.3 18.6
268 Sept. 25 18.9 -0.2 9.4 18.4
269 Sept. 26 14.9 3.5 9.4 17.0
270 Sept. 27 17.8 -1.5 7.3 18.2
271 Sept. 28 21.1 3.6 11.5 17.7
272 Sept. 29 22.9 9.8 15.8 17.0
273 Sept. 30 22.8 3.9 12.8 17.1
274 Oct. 1 26.1 7.1 15.3 15.3
275 Oct. 2 19.0 7.7 14.7 3.8
276 Oct. 3 11.7 0.0 6.9 15.3
277 Oct. 4 15.0 -3.1 5.3 16.6
278 Oct. 5 17.4 0.1 9.0 7.9
279 Oct. 6 15.1 7.8 11.5 10.2
280 Oct. 7 9.6 2.9 6.6 6.9
281 Oct. 8 11.2 -2.0 3.9 11.1
282 Oct. 9 11.5 -5.5 3.0 13.1
283 Oct. 10 11.5 5.7 8.5 4.0
284 Oct. 11 20.5 1.9 11.8 14.8
285 Oct. 12 24.4 4.4 15.7 15.3
286 Oct. 13 27.2 1.7 12.8 14.6
287 Oct. 14 28.8 9.0 17.3 12.6
288 Oct. 15 28.1 9.8 18.0 10.7
289 Oct. 16 21.8 7.3 14.6 6.3
290 Oct. 17 7.3 2.4 3.9 2.2
291 Oct. 18 6.3 -1.5 1.5 9.0
292 Oct. 19 0.8 -0.9 0.1 2.2
293 Oct. 20 3.2 -0.1 1.0 3.0
294 Oct. 21 20.4 -2.4 6.4 4.4

120

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Appendix 4.

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20 4o 60 80 160'120'110'160

Height to Top Leaf Ligule (cm)

Relationship between above ground biomass and

height to the top leaf ligule from data taken during 1989.

221

 

 

 

PA 90"
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+5 80- smalou - 3.02 x10 ‘(00) + 0.89
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0 20 40 '60 '80 300 120 140 3330 380 200

Height to Top Leaf Ligule (cm)

Appendix 5. Relationship between stem biomass and height to
the top leaf ligule from data taken during 1989.

222

 

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0 1000 2000 3000 4000 5000 6000 7000
2

Plant Leaf Area (cm )

Appendix 6. Relationship between leaf biomass and plant leaf
area from data taken during 1989.