ABSTRACT

RELATIONSHIPS BETWEEN CULTURAL PRACTICES AND
MORPHOLOGICAL AND PHYSIOLOGICAL CHANGES IN

PICKLING CUCUMBER (CUCUMIS SATIVUS L.)

 

By

Jose Miguel Fernandez

This is a study of the behavior of different varieties of pickling cucumber
for once-over harvest planted at different plant populations under various cultural
and environmental conditions.

Field experiments were conducted during 1969 to study the effect of plant
density, supplemental nitrogen, and 2 types of irrigation on the growth and de-
velopment of three varieties of pickling cucumbers. An attempt was made to
place the yield and quality of cucumber fruits on a more exact morphological,
physiological, and ecological basis that might help in the development of varieties
suitable for high density planting.

Results indicated that supplemental N levels (33. 5 and 67.0 lbs/acre),
applied when the flowers began to appear, increased the leaf area per plant,
the percentage of gynoecious plants, the number of fruit and usable yield, and
value. As the plant population increased the need for N increased, suggesting
that N was the most important nutrient under conditions of high plant populations.

"Misting" (application of 0. 05-0. 06 inch of water per hour from 10 a. m.
to 3 p. m.) during periods of high atmospheric stress had a direct beneficial

effect on growth and development of cucumber plants as compared with -

Jose Miguel Fernandez

conventional irrigation used to maintain soil moisture. "Mist" irrigation in
this experiment increased the internode length, leaf area per plant, number of
fruits, usable yield, and dollar value, principally in the low and intermediate
plant populations.

As the plant population increased the internode length increased, but
the number of nodes, average leaf area, leaf area per plant, and number of
leaves decreased; however, the total yield increased, but the usable yield was
not influenced.

Under conditions of high plant populations, the competition for light at
the end of the growing season had a marked detrimental influence on the gross
photosynthetic rate, resulting in a significant decrease in crop value.

"Mist" irrigation and supplemental nitrogen increased the gross photo-
synthetic rate calculated by a light/photosynthetic mathematical model. Varieties
behaved differently under the conditions studied; WU 8821 was shown to be more
adaptable to high plant populations because of certain morphological and growth

characteristics.

RELATIONSHIPS BETWEEN CULTURAL PRACTICES AND
MORPHOLOGICAL AND PHYSIOLOGICAL CHANGES IN

PICKLING CUCUMBER (CUCUMIS SATIVUS L.)

 

By

Jose Miguel Fernandez

A THESIS

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

MASTER OF SCIENCE
Department of Horticulture

1970

QCoZOC/g
5 — I? '70

AC KNOW LEDGMENTS

The author wishes to express his sincere thanks and appreciation
to Drs. C. W. Nicklow and R. L. Carolus for their assistance and
guidance in the planning and analysis of this study and to the other
members of the guidance committee: Dr. A. A. De Hertogh, Dr. L. R.
Baker, Dr. A. L. Kenworthy and Dr. A. E. Erickson.

Appreciation is also expressed to Dr. Charles Cress for his
assistance in computer analysis. The financial support of a Gerber
Baby Food Fund assistantship is gratefully acknowledged.

Finally, special appreciation is expressed to my wife, Ana Cecilia,

for her patience, help, and encouragement during my graduate studies.

ii

TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS........... ........ . 11
LIST OF TABLES................................................... 'v
LIST OF FIGURES. vii
INTRODUCTION..................................................... 1
REVIEW OF LITERATURE.... ................ ......... ....... 3
Introduction.................................................. 3
Factors That Can Limit Growth and Productivity of Plants...... 4
Relationships Between Limiting Factors and Plant Morphology... 13

Relationships Between Light Distribution, Physiology of Plant
Growth, and Productivity.................................. 24

MATERIAL OF METHODS.......................................... 33
I, Nitrogen Level............. ................. ................ 33
II. Irrigation Systems........................................... 34

III. Morphological Measurements................................. 36
IV. Physiological Measurements.................................. 41
RESULTS.......................................................... 49

I. Relationships Between Cultural Practices and Morphological
Changes in Different Varieties in Pickling Cucumber........ 49

(A) Internode Length and Number....................... 49
(B) LeafArea and Leaf Area Index..................... 54

(C) Harvest Date ................... .. 60
(D) ,Sex Expression.................................... 63
(E) Fruit Set.. ...... ... 63
(F) Yield and Relative Value................. ..... ..... 69

II. Relationships Between Cultural Practices and Nutrient Com-
position in Different Varieties of Pickling Cucumbers........ 81

(A) Macronutrients..................................... 81

(B) MicronUtrientSOCOOOOO.00.0.....OOOOOOOOIOOOOOOOOOOOO 84

III. Relationships Between Cultural Practices, Light Distribution,
Physiology of Plant Growth, and Productivity in Different
Varieties of Pickling Cucumber..... .. ..... ...... ..... ...... 86

iii

Page

(A) Light Above and Below the Canopy ....... . ....... . . . 86
(B) Extinction coeffi-Cient. O O O O O C O O O O O O C O C O O C O O C O O O O O C O . 86
(C) Photosynthetic Rate. . ............... . ...... . . . . . . . . 90

DISCUSSION. . . . . . .

. 102
LITERATURE CITED......

......OOOOOOOOO 105

iv

Table

4.

10.

LIST OF TABLES

Page

Leaf area in square inches per leaf, number of leaves per
plant, leaf area in square inches per plant, leaf area
in thousands of square inches per plot, and leaf area
index as affected by variety, plant population and Nlevel. 57

Leaf area in square inches per leaf, number of leaves per
plant, leaf area in square inches per plant, leaf area
in thousands of square inches per plot, and leaf area
index as affected by variety, plant population and
systems of irrigation.. .......... . ............ . ........ 59

Number of days from planting to harvest as affected by
variety, plant population and nitrogen level. . . . ......... 61

Number of days from planting to harvest as affected by
variety, plant population, and systems of irrigation ..... 62

Effect of two varieties, at three plant populations, and
three levels of nitrogen on the percentage of gynoer-
cious and monoecious plants. .......... 64

(a) Effect of three varieties and two systems of irrigation,
and (b) effect of three varieties on the percentage of
gynoecious and monoecious plants ....... . . . . . . . . . ..... 65

Total number of fruit per plot, average number of total
and usable fruits per plant for two varieties in each
of three plant populations and three levels of nitrogen. . 67

Total number of fruits per plot, average number of total
and usable fruits per plant for three varieties each
at three plant populations and two systems of irriga-
tion............ ................. 68

Yield 08 six grades of cucumbers, percentage and quantity
of nubs, and marketable fruits for each of two varieties
in three plant populations with three levels of nitrogen. 74

Value per acre of six grades of pickling cucumbers and the

average value per bushel for each of two varieties, at
three plant populations, and three levels of nitrogen.. . 76

V

Table Page

11. Yield of six grades of cucumbers, percentage and
quantity of nubs, and marketable fruits for each of
three varieties at three plant populations with two
systems of irrigation. . . . . . . ..................... . . . . . 77

12. Value per acre of six grades of pickling cucumbers and
average value per bushel for three varieties each at
three plant populations and with two systems of
irrigation... ...... 82

13. Amounts of N, P, K, Ca and Mg (Total and Soluble) found
in cucumber plants on the basis of dry and fresh
weight.. ....... 83

14. Amounts of total Mn, Fe, Cu, B and Zn found in cucumber
plants on the basis of dry weight..................... 85

15. Extinction coefficients calculated for each variety at three
plant populations in Experiment 1 (a) and Experiment

2 (b)................................................ 89

16. Total bushels per acre, dollar value per acre, percentage
of nubs and the area under calculated photosynthetic
curve for two varieties, each at three plant populations,
and with three levels of nitrogen...................... 95

17. Total bushels per acre, dollar value per acre, percentage
of nubs, and the area under calculated photosynthetic
curve for three varieties each at three plant populations,
and two systems of irrigation..........................101

vi

LIST OF FIGURES

Figure

1. Daily minimum and maximum temperatures (OF) and
cumulative daily precipitation (inches). . . . . . . . . . . . . . .

2. Cumulative (daily) solar radiation tOtals in langleys in
relation to date, between July 1 and August 19, 1969.

3. SR-Spectroradiometer (ISCO) with the movable sensing
headl used to obtain light intensity (in pW Cm
mu- l)3.b0V€ and below the CaIIOPYOOOOOOOOOOOOOOOOOO

4. Rates of photosynthesis expressed in mg COg/dm2 of
leaf surface/hour for Cucumis sativus L. "Var.
Ohio 47" plants in steady light at various levels
of photosynthetically active radiation. . . . . . . . . . . . . . . .

 

5. lntemode length (in inches) and average number of inter-
nodes (on the top of bar graphs) at three stages of
growth of two varieties and three plant populations. .

6. Internode length (in inches) and average number of
intemodes (on top of bar graphs) at three stages
of growth of three varieties, at three plant popula-
tions and two systems of irrigation................ .

7. Internode length (in inches) and average number of
intemodes (on top of bar graphs) at three stages
of growth of three varieties with two systems of
irrigation.........................................

8. Number of fruits per plot, and average number of total
and usable fruits per plant at two systems of irri-
gation and three plant populations. . . . . . . . . . . . . . . . . .

9. Number of fruits per plot and plants per acre for three
varieties at three spacings........................

10. Plants per acre, total usable fruit in bushels, total

value per acre in dollars for each of three varieties
at three plant populations..........................

vii

Page

37

42

45

47

50

52

55

70

72

79

Figure Page

11. Light spectral distribution above and below the canopy
of a pickling cucumber planting with 188, 000 plants
per acreOOOOOOOOOOOOOOOOOO......OOOOOOOOOOOOOOOOOOOO 87

12. Gross photosynthetic rate for the variety, Pioneer, at three
plant populations and three levels of nitrogen, during
the perj-Od Of grOWthOOOOOOOOOOOO......OOOOOOOOOOOO... 91

13. Gross photosynthetic rate for the variety, Spartan Progress ,
at three plant populations and three levels of nitrogen
during the period of growth........................... 93

14. Gross photosynthetic rate for three varieties each at three
plant populations with mist irrigation during part of
the growmg periOdOOOOOOOOOOOOOIO......OOOOOOOOOOOOOO 97

15. Gross photosynthetic rate for three varieties each at three
plant populations with conventional irrigation during
part Of the growmg periOdOOOOOOOO......OOOOOOOOOOOOO 99'

viii

INTRODUCTION

Cucumbers for pickles are one of the most important vegetable processing
commodities in the United States. In Michigan, they provide an on-farm value
of around 10 million dollars annually.

Due to labor shortages in recent years, mechanization of harvesting has
been intensively studied. In order to harvest mechanically, investigators have
been concerned not only with the principles and components of the once-over
harvester, but also in the development of suitable varieties and cultural prac-
tices for economic production.

Cucumber varieties are normally monoecious in flowering habit (pistillate
and staminate flowers on the same plant). The introduction of the gynoecious
character (plants with all pistillate flowers) by Peterson and Weigle (1958)
resulted in the development of gynoecious pickling cucumber hybrids. They
develop pistillate flowers earlier than the monoecious varieties and produce
a concentrated fruit set which results in higher yields. These characteristics
have made once-over harvest feasible, Peterson (1960).

The economic success of once-over harvest depends on many other
factors. Some of these are a short internode vine type, a low ratio of vege-
tation to fruit, disease resistance and fruit quality characteristics acceptable
for processing. All these characteristics are needed in order to achieve a

high yield at a single harvest. However, due to the sequential development

of flowers and the fact that one to a few developing fruits can prevent sub-
sequent fruit development in a gynoecious cucumber plant, a large number
of usable fruits are not produced at a given time. Hence, increasing the
plant population per acre is one method of increasing the yield per unit
area of land for a single harvest, Stout gt _a_._l_: (1963).

An increase in competition among plants for nutrients, light, water
and C02 in high density stands will likely require changes in other cultural
practices. As plant populations increase and the competition among plants
increases, some varieties behave differently than others and give a different
response especially in yield, Nicklow (1968).

This is a study of the behavior of different varieties at different plant
populations under various cultural and environmental conditions. Also, the
influence of morphological, physiological and ecological factors on yield were
evaluated. .This may help in the development of varieties suitable for high

density planting and mechanical harvest.

REVIEW OF LITERATURE

Introduction

Since the development of the first gynoecious pickling cucumber F1
hybrid, Spartan Dawn, several other gynoecious hybrids have been developed
and evaluated under a wide range of plant populations, for a once-over
destructive harvest.

Morrison and Ries (1967) reported yield and dollar value per acre
increased with an increase in plant population from 4, 100 to 77,880 plants
per acre, using the varieties, Spartan Dawn and NBU FC-ll. In subsequent
experiments, neither the yield nor the dollar value per acre increase using
plant spacings closer than 9 inches between rows and 9 inches between
plants in the row (9" x 9") or 77,880 plants per acre.

With the same plant spacing, 9" x 9" or 77,800 plants per acre, 10
gynoecious varieties showed a wide variation in their ability to produce high
yields at this high plant population in work reported by Nicklow and Woolsey
(1968). Using a gynoecious cucumber hybrid, Spartan Advance, which pro-
duced high yields in the previous experiment, the same authors show ed that
increasing the plant population to 251,000 plants per acre or 5" x 5", re-
sulted in a dollar value significantly higher than from plants spaced 9" x 9".

Fruit yield of plants is produced in the course of the processes of

their life during vegetation, reproduction and development. According to

Nichiporovich (1960), high yields are obtained if the plant's needs are met

in the optimum manner throughout the entire growing period; if the plants

are steadily supplied with food and water; if the nutrients are well assimilated;
if they are utilized in the best way for growth, formation and development

of those organs, which are initially essential for the feeding and growth

of the plant itself (roots, leaves) and later for the formation of organs con-
stituting the economical part of the yield (fruits, bulbs, grains, etc. ).

Hence, the difference in behavior of cucumber varieties at high plant
populations may be due to a different behavior of the plants during the entire
growing season, showing a different response to limiting factors under condi-
tions of extreme competition among plants. It is anticipated that accompanied
with these differences are morphological and physiological changes which in-
crease the efficiency of the plants to meet their requirements for optimum

growth.

Factors That Can Limit Growth and Productivity of Plants

According to Blackman (1905), productivity of plants is determined by
the activity of the photosynthetic mechanism. The most important factors
controlling photosynthesis are nutrients, moisture, temperature, carbon dioxide
and radiant energy.

In high density plantings, one or several of these factors might limit

the growth and productivity of a crop.

Nutrients

The nutritional requirements of pickling cucumber have been studied
intensively in conditions of low and relatively high plant populations. The
work of Cooper and Watts (1934) revealed that P was often the most limiting
element, followed by N and K.

At different locations in Michigan, Wittwer and Tyson (1950) concluded
that the application of 500 pounds per acre of 3-12-12 fertilizer was profitable
with pickling cucumber in fairly productive soils. Also, they concluded that
supplemental N was not beneficial, except on poorly drained soils of low
fertility.

Working with 4 different spacings (6, 12, 18, 24 inches apart in 5 feet
rows), Ries (1957) found that yield was not influenced by fertility levels. With
the same spacings in the row but with rows 4 feet apart, he found that the
highest yields were obtained from plots with close spacing and supplemental
fertilizer, 100 pounds of NH4NO3 with 200 pounds of 12-12-12 per acre, during
a season of heavy rainfall.

Miller (1957) working with greenhouse conditions, found N was the most
limiting factor in the growth of pickling cucumber. He found that 3 times
more marketable fruit was produced by the high N application. Under field
conditions, he found highest yields were produced in plots receiving 100 pounds
per acre of 5-20-20 in a side-place application. He noted, also, that the

variety, SMR-12, has a better foraging ability than Wisconsin 70.

Ries and Carolus (1958) found that there was no increase in yield
from application of either 'Mg or supplemental N in a season of above
average rainfall; although it appeared that the addition of supplemental N
counteracted some detrimental effect of high K. They, also, pointed out

that the lack of either nitrogen or phosphorous or both delayed maturity.

Moisture

Slatyer (1969) reported that all plant processes took place in what was
effectively an aqueous medium. Because water was involved as either a
transporting agent or reactant in many of these‘processes, it was not sur-
prising that reduced water uptake and dehydration could have deleterious
on most physiological processes.

According to Kramer (1963), water stress or water deficit has multiple
effects on plant growth, but the most important one is the reduction in the
rate of photosynthesis by the reduction of leaf area, closure of stomata, and
reduction of the dehydrated protoplasmic machinery.

In tomato leaves, Brix (1962) found that a Diffusion Pressure Deficit
(DPD) of 7 atmospheres was required before photosynthesis was reduced.
Higher DPD resulted in higher reductions, and at 14 atmospheres net photo-
synthesis was zero. In leaves the rate of respiration was affected by water
stress with a steady decrease with a DPD above 8 atmospheres. He, also,
found that the rate of transpiration and photosynthesis change was quite

similar, thereby indicating that photosynthesis was affected by water stress

because of an increased resistance to gaseous diffusion.

Using cotton leaves, Boyer (1965) found that both photosynthesis and
respiration were reduced at least 25% at -8. 5 bars (106 dyne/cmz). In all
cases, stomata were fully open indicating that only part of the photosyn-
thesis reduction (and the large decrease in growth) could be attributed
to stomatal closure.

Decreasing the water content in cotton leaves from 96 to 56% re-
sulted in an increase in the calculated diffusive resistance and a decrease
in CO exchange. Under these conditions, T roughton (1969) found that

2

plant water status primary affects CO exchange by regulating stomatal

2
aperture. The mesophyll resistance, which was estimated in air and in
oxygen-free atmosphere, did not vary with the relative leaf water content
when reduced to 75%, but increased progressively as relative water content
dropped from 75 to 56%.

Greenfield (1942) working with plants without stomata, showed a reduc-
tion in photosynthesis with an increase in water stress. From the results
of Boyer (1965) with cotton leaves which showed a decrease in photosynthe-
sis under high water stress with the stomata fully open, appears to give
evidence that a decrease in hydration of protoplasm also directly reduced
photosynthesis.

Nichiporovich (1968) noted that the general state and the activity of

the photosynthesizing apparatus changed to a large extent during the day,

becoming particularly unfavorable at the middle of the day.

Working with corn plants growing in a chamber at 1 atmosphere soil
moisture tension and at 1 inch Hg vapor pressure deficit, Baker and Mus-
grave (1964) showed a light saturation at 10 a.m. Under these conditions
the rate of apparent photosynthesis was reduced 50% and more in the middle
of August. The rate of photosynthesis behaved in a similar manner to
transpiration, suggesting either stomatal control or an increase in mesophyll
resistance proportional to an increase in stomatal resistance.

Leaves of Phoenix reclinata Jacq. responded to both high temperature and

 

water stress, with a sudden and marked increase in their minimum inter-
cellular space carbon dioxide concentration according to work by Meidner
(1961). He concluded that the phenomenon of midday closure of stomata may
be due to either of these two factors or both interacting together.

In tomato and cotton the response patterns showed a close relationship
to water stress. In both crops, Slatyer (1967) found that growth (expressed
as total dry weight) and stem elongation, did not continue beyond a stress
value that resulted in zero turgor pressure in the tissue of adult leaves.

Also, in Sorghum vulgare L. , Helianthus armus L., GOSS)Q1um hirsutum L. ,

 

 

and Thespesia pulpunea (L.) Soland, El-Sharkany and Hesketh (1964) reported net

 

photosynthetic rates depressed by high water deficits and high temperatures.

Temperature and Carbon Dioxide

 

The normal C02 content in the atmosphere of 0.03% can be reduced

during the day to 25% below the normal. According to Chapman and Loomis

(1953), this limitation in C02 supply can explain the low temperature coefficient
of photosynthesis in the field of 1.0 in contrast to 2.0 or more in laboratory
conditions with C02 concentrations 100 to 200 times normal.

Gaastra (1959) reported that, using leaves from sugar beet, turnip,
tomato and cucumber plants growing in 0.03% C02, photosynthesis was almost
independent of leaf temperature, while at higher concentration, the rate is
strongly affected by temperature, so that light saturation was not reached at
the highest temperature (31 to 35°C). At high light intensities, he found the
relationship between photosynthesis and C02 concentration to be linear in the
concentration range from 0 to O. 03%.

In cucumber plants, Hopen (1962) found that C02 and light functioned
as compensative growth factors. As light levels were intensified up to 1,400
footcandles, the growth of cucumber plants increased at a more rapid rate
with higher levels of C02 than under low levels. At the higher 002 concen-
tration studied (2150 ppm), light was shown to be a limiting factor at a light
intensity range from 1,000 to 1,400 footcandles. He concluded that C02 and
light could be limiting factors for field cucumber growth under conditions of

high plant p0pu1ation.

Light
The energy of light from the sun, according to Anderson (1964), ulti-

mately drives all biological and meteorological processes. On striking the

earth's surface, some of the absorbed light may be reradiated as heat,

10

driving atmospheric processes, some may go to evaporate water from the
soil and plants while a small portion, 5-6% at most, may be used in
photosynthesis .

Photosynthesis is not only affected by the duration and intensity of
light, but also the quality. According to Loomis _e£ a_l_. (1967), the number
of quanta, or the energy and spectral distribution in the 0.4 to 0.7 mi-
crons (n ) region, is the most important.

According to Saeki (1960), within a plant community, incident light
intensity diminishes on account of light absorption, for the most part, by
the leaf laminae. So the area of the leaves and their mode of distribution
are no doubt the major determinant of light distribution inside the plant
community. If I' is the light at any level with the canopy, and I0 the
incident light above the canopy, the mean relative light intensity will be
I'/Io. Expressing I'/Io, prevailing at any level of the plant canopy as a
function of the total leaf area of plants per unit stand area (Leaf Area
Index or L), the illumination intensity at each leaf surface can be calculated
by the formula; I'/Io = exp (-KL). Where (K) is the extinction coefficient
determined by the transmissibility, arrangement, and especially the inclination
of leaves.

The extinction coefficient (K) is characteristic of each plant community.
Monsi and Saeki (1953) reported that in communities with more or less
vertical leaves the extinction coefficient (K) on both theoretical and practical

grounds was usually 0.3 to 0.5, and for communities with nearly horizontal

11

leaves was 0.7 to 1. 0.

The relationship between the photosynthetic rate of leaves and light
intensity (at normal C02 concentrations, 0. 03%) has been determined by
several investigators. Gaastra (1958) reported that photosynthesis curves
provide the basis for interpretation of data on solar energy conversion
in field crops, derived from harvest data and simultaneous records of
incident solar radiation.

De Witt (1959) found that the relationship between photosynthetic rate
of leaves and light intensity was largely unaffected by temperature within
the normal temperature range and was substantially the same for several
agricultural crops. Therefore, the photosynthesis in a crop surface would
depend on: a) photosynthetic curve of single leaves, b) position of leaves
with respect to direction of light, c) direct and diffuse light intensity, d)
natural shade of leaves, e) soil coverage by the leaves, and f) carbon dioxide
concentration of atmosphere.

According to Saeki (1960), light photosynthesis curves obtained in con-

trolled conditions could be well approximated by a rectangular hyperbolae

equation, P = W , where (P) is the gross rate of photosynthesis, (I) is
the light intensity, (Pmax) is the maximum rate of photosynthesis (horizontal
asymptote of the curve), (k) is the half saturation light intensity. The con-
stants (Pmax) and (k) define the shape of the curve.

McCree and Loomis (1969) reported that in cucumber plants the light-

response curve was similar to those commonly found for dicotyledoneous

12

species. They found the maximum photosynthetic rate in this case was 29
milligrams of 002 per din2 (mg COz/dmz) of leaf surface per hour, being
reached at about 150 watts per square meter per hour (W /m2/hour) of
photosynthetically active radiation, with a half saturation light intensity of
about 40 W/mZ/hour.

Baker and Musgrave (1964) found in field conditions, very high corre-
lations between the radiation measured on a flat horizontal surface and the
rate of photosynthesis in a corn stand. This indicated that the response
curve could be fitted to a curve used for a single leaf.

From the analysis of the angle of incidence of the sun's rays, the
spectral composition of the radiation, and the relative intensity of diffuse
radiation from blue sky, haze, clouds, and of direct radiation from the
solar beam, Monteith (1969) found that the fraction of photosynthetically active
radiation (PAR) was surprisingly constant at 50% of total radiation when the
sun was more than.20 degrees above the horizon.

The rate of photosynthesis per unit leaf area is usually measured in
controlled conditions, in steady, artificial light, but in nature the most com-
mon condition is fluctuating light. McCree and Loomis (1969) demonstrated
that in fluctuating light, both natural and artificial, the photosynthetic rate
was always within a few percent of that calculated from the steady-state
rates. In other words, when the light was reduced but not' extinguished, the
plants (cucumber) acted as near-perfect integrators for all periods of alter-

2

nating light between 10' and 10+3 seconds.

13

From these studies, it may be expected that the gross photosynthesis
of a field crop would be: a) relative insensitive to daytime temperature
changes during the growing season, b) strongly dependent on the intensity
of radiation and its distribution below the canopy, and c) approximately pro-
portional to the concentration of carbon dioxide in air surrounding the leaves.
Monteith (1965) found that within the plant canopy the minimum concentrations
of 002 were usually between 290 and 250 ppm and rarely fall to 200 ppm.
He concluded that the local deficit of C02 within the canopy was about 10
percent of average which was not considered as a serious limiting factor in

crop growth.

Relationships Between Limiting Factors and Plant Morphology

Recognition of the fact that interpretation of the phenomena of flowering
and fruiting requires a clear understanding of the vegetative processes that
precede them, has stimulated numerous studies of factors affecting growth of

plants from germination to maturation.

Internode Legth

 

Stem growth characteristics, determined by the number and length of
intemodes, have been studied under different conditions.

Miller (1957) observed that plant growth was slower and internodes were
shorter on cucumber plants in cool conditions (60°F) than in warm conditions
(70°F). Both Dearborn (1936) and Miller (1957) reported that cucumber plants

growing under conditions of low N developed stiff and woody stems with slower

14

height growth than those on high N.

Hopen (1962) found that the addition of 25% more C02 at realistic
natural levels up to 2150 ppm increased the number of internodes developed
and the height of the cucumber plants. The number of intemodes increased
with the highest levels of radiant energy (1400 foot candles) and the higher
C02 levels (450 ppm). As the radiant energy increased from 300 to 1400
foot candles, the height of cucumber plants decreased and the number of
intemodes increased. Hence, the intemodes were shorter at high light
levels.

It is well known that light inhibits stem elongation of an intact plant
compared with the exclusion of light. Mohr (1964) reported that the internode
length was affected not only by the quantity, but, also the quality of light.
He showed that the maximum inhibition effect was in the red wavelengths
which was reversed by far-red light.

Also, the duration of the photoperiod (daylength) affects cucumber
plant length, number of intemodes, and the contour of the stems. Danielson
(1944) found that in terms of stem length, the twelve-, eight-, and sixteen-
hour plants were longest, intermediate, and shortest, respectively, at 63
days of growth. But during the ensuing two weeks the growth pattern was
considerably altered, and at the age of 95 days the eight-, twelve-, and
sixteen-hour plants were longest, intermediate, and shortest, respectively.
The contour of the stems of the internodal diameter measurements showed

that the sixteen-hour stems were approximately twice as thick at their

15

greatest diameter as the eight-hour stems. The thickness of the twelve-hour

stems was intermediate with respect to those of the other groups.

Leaf Area

 

According to Nichiporovich (1960), productivity of plants may be deter-
mined by the course of growth and the size of the photosynthetic mechanism
(the leaves) and by the net productivity of photosynthesis. The speed of
formation and growth of the leaves, the duration of their life activity, and
the intensity of their activity usually depends on the nature and properties of
the plant itself, and on the conditions of water supply, nutrition, light, C02,
photoperiod, etc.

Vegetative growth may be particularly sensitive to water deficits as
reported byKramer (1969) because growth was closely related to turgor and
loss of turgidity stops cell enlargement resulting in smaller plants. For the
same reason, leaf area was usually reduced in conditions of water stress,
indirectly decreasing photosynthesis.

Milthorpe (1956) found that nutrition primarily affected the leaf area.
His work showed that N increased the leaf area in the growth period. P
increased the leaf area in the beginning of the growth period, and K delayed
senescence of the leaves.

Working with cucumber plants growing under conditions of low N, Miller
(1957) and Dearborn (1936) reported that they developed a pale green foliage,

while plants growing under high N conditions were dark green and succulent.

16

They have clearly shown that a high N level materially increased plant
activity in producing green and dry matter, and that fruit development
took place at the expenses of the growth of other parts of the plant.

The importance of carbohydrate/N ratio in connection with the growth
and development of plants was first pointed out by Kraus and Kraybill
(1918). Larger size of leaves and stems was not always connected with
higher yields. Plants grown with an abundant supply of N were dis-
tinctly vegetative and non-fruitful, with a higher N03 -N and low free re-
ducing sugars, sucrose and polysaccharides, than the less vegetative
plants.

It has been demonstrated in rice and other crops by Tanaka e_t_ El:
(1965) that when the N uptake was large in comparison to the available
light energy, the plants suffered a shortage of carbohydrates, leading to a
decomposition of the protein and the accumulation of amino acids, amides
and eventually ammonia with a consequent death of leaves. Cucumber
plants, grown at excess levels of N, showed similar necrosis at the tips
of the leaves (T iedjens, 1928).

Hopen (1962) observed that leaf size and leaf starch contents of cucumber
plants were increased when C02 was added to the atmosphere.

The effect of light intensity, light spectrum and light duration has been
studied extensively. Parker e_t g. (1949) found that leaf area increased as
the light energy increased from 0. 1 to 10,000 erg/cmz/day. Dows (1955)

reported that red light was most effective in stimulating leaf enlargement.

17

This red light effect was reversed by far-red light.

Working with different photoperiods or daylengths, Danielson (1944)
found that the largest cucumber leaf area per plant occurred in the twelve-
hour plants, the sixteen-hour plants were intermediate and the eight-hour
plants had the smallest leaf area. Leaves of the sixteen-hour plants were

thicker than those from plants grown in the shorter daylengths.

Sex Expression

 

Due to the economic importance of cucumber plants, the sex ratio has
been studied in detail in relation with various environmental conditions.

Since the early work of Tiedjens (1928), the importance and direct in-
fluence of factors such as light and nutrition on sex expression of cucumber
plants have been known. He found that the total number of both staminate
and pistillate flowers was less on plants grown in soil low in N than those
grown in soil high in N. An abundance of light tended to increase the number
of staminate flowers, but the reduction of light increased the number of pis-
tillate at the expense of staminate flowers. He found that a reduction in the
duration of the daylength decreased the number of staminate flowers. The
main conclusion was that the environment did not cause a change from a
staminate to a pistillate flower condition, but rather caused a change from
one to the other type of flowers to leaf and stem tissue. In other words,
the environment merely produced conditions which made possible the expres-

sion of potentialities of the plant. Dearborn (1936) reported that on low -N

18

plants, fewer pistillate flowers were produced when the young fruits were
removed than on normal fruiting plants.

Cucumber plants, known as the small gherkin (Cucumis anguria L.),

 

growing in different photoperiods showed differences in flowering responses
according to work of Danielson (1944). These differences were quantitative
rather than qualitative. Ten plants in the eight-,‘ twelve-, and sixteen-
hour groups produced totals of 964, 647 and 465 blossoms, respectively.
Maximum staminate flower production, on the basis of the total number of
flowers produced, occurred in the eight-hour day.

Using two air humidities at two temperatures (89% at 230C, and 50% at
300C) and two soil moistures (80% and 40% of total moisture capacity),
Mining (1944) found that cucumber plants were more susceptible to these
conditions in the period when the parts of the flowers were being formed.

At 50% humidity and 30°C the appearance of male flowers were accelerated
while the female flowers were impeded. The effect of the high humidity and
temperature condition was entirely different. The rate of appearance of fe-
male flowers increased, whereas that of male flowers lagged behind. In

this latter growing condition, sexual developments assumed a course towards
a greater manifestation of female tendencies. Similar results were obtained
by Mining (1944) using different soil moistures, humid soils promoted a more
rapid and stronger manifestation of female flowering.

Using "Acorn" squash (Cucurbita pepo L.), pickling cucumber and

 

19

gherkin (Cucumis anguria L.), starting from the first leaf, Nitsch Etfl° (1952)

 

observed the following sequence of flowers: underdeveloped male, normal
male, normal female, inhibited male, giant female, and parthenocarpic female
flowers. Climatic factors (daylength and temperature) affected the deveIOpment
of these flower types. High temperatures and long days tended to keep the
vines in the male phase, whereas low temperature and short days sped up the
development so that the female phase was reached after a lower number of
nodes, with the percent of female flowers rapidly becoming 100%. Also, they
pointed out that the climatic factors modified the length but not the order of
the phase.

Peterson and Weigle (1958) found that the sex expression of gynomonoecious
breeding lines segregated gynoecious plants at two locations, but the degree of
female expression was affected by environmental conditions. In Colorado, con-
ditions only 29.4 percent of the plants were gynoecious as compared to 49.7
percent in Michigan.

Miller (1957) reported that night temperature, daylength and N level mar-
kedly influenced the sex expression on monoecious pickling cucumbers. Rela-
tively more pistillate flowers were produced by high than by low N conditions.
Of the factors studied, night temperature was the most influencial in production
of pistillate flowers. Relatively more pistillate flowers were produced under
cool (600F) tlmn warm (70°F) night temperatures. High N and warm tem-
perature resulted in high numbers of staminate flowers per plant. On the

other hand, more pistillate flowers per plant were produced with high N and

20

cool temperature.

One of the most important characteristics of cucumber plants has been
the inhibitory effect of developing fruits on further growth and development
of the plant. Tiedjens (1928) observed that if the pistillate flowers were
all pollinated and fertilized, the first fruits start to grow producing an
inhibitory effect on those pollinated later. He found that the extent of
this inhibition is manifested differently in different plants. For example,
one plant may develop only one fruit, while another may develop six fruits
before the inhibitory effect is observed.

Tiedjens (1928), also, found that removal of the staminate flowers at
anthesis increased the production of pistillate flowers and reduced the ratio
of staminate to pistillate flowers at least 40 percent. As the fruits were
removed when mature, flowering began again, but few staminate flowers
were produced with the result of the pistillate flowers improperly fertilized
and the fruit did not develop well.

Dearborn (1936) studied the same phenomenon under different N levels
and found that under low and high N levels, normal-fruiting plants produced
the greatest amount of total fresh weight (including the fruit) and deflorated
plants produced the least. Deflorated plants produced fewer staminate
flowers than did either plants with the fruit removed or those allowed to
fruit normally, with either high or low N nutrition. The ratio of staminate
to pistillate flowers and the percentage of fruit set were also modified by

the removal of fruits and/or flowers. The widest ratio resulted from

21

removing young fruits from the low N plants. Defloration gave the narrowest
ratio. The percentage of flowers which set fruit was increased materially
by the removal of young fruit.

These workers concluded that sex expression in cucumbers was deter-
mined by genetic factors. The effect of the presence of fruit and various

environmental conditions may be seen, but their influence confined within

certain limits established the genetic composition of the plant.

Fruit Set and Development

 

Fruit growth and development, as well as their physical characteristics,
may be affected by environmental factors. These factors may determine
the quality and quantity of pickling cucumber fruits.

Among nutritional factors, T iedjens (1928) reported that N was important
for quality of pickling cucumber fruits. N improved the shape of the fruits
even in flowers which were pollinated previous to the application of urea.

Dearborn (1935) showed that more fruits of greater weight were produced
on high N than on low N levels. Fruits from the low-N plots, without ex-
ception, were of poor market quality. Fruits were curved and misshapen
with a pale green yellowish color. Fruits from the high-N plots were all
of excellent color, straight, and well shaped. Also, it was found that the
development of fruit had less effect on the growth and chemical composition
of the plant when the N supply was adequate than when it was low. High-

N plants, in general, had higher percentages of all forms of N than low—

N plants of the same type.

22

According to the work of Miller (1957), approximately three times as
many marketable fruit were produced by high-N as by the low-N plants.
Fruits from the low N plants were lighter green than from the high-N
plants. Also, the high N level increased the length to diameter ratio of
the fruits of two varieties tested.

Pickling cucumbers were grown in sand culture by Reynolds and Stark
(1953) with N at 5, 10 and 20 milliequivalents per liter (meq/l), Mg at
1, 3 and 9 meq/l, K at 3, 6 and 12 meq/l, and Ca at 4, 8 and 16 meq/l.
Variations in N level produced the predominant effect on vegetative growth
at all stages. The greatest weight and number of fruits resulted from the
medium N level with a slight decline in fruit production at the highest con,-
centration. The medium N level also resulted in the lowest percentage
of malformed fruits atrl the earliest production of pistillate flowers. Fruit
production increased and the percentage of malformed fruit decreased with
each increase in Mg level. The K levels employed apparently had little
effect on fruit production. The lowest concentration of Ca employed was
apparently adequate and higher concentrations reduced growth. Significant
interactions indicated that the toxic effect of high Ca was greatly reduced
when it was present in combination with the high level of N, and the high
K in combination with low Mg accentuated Mg defficiency. High K in com-
bination with low Mg resulted in reduced growth and fruiting, but the high

K in combination with medium or high Mg increased growth and fruiting.

23

Daylength and temperature also affect the pickling cucumber fruits. In
conditions of low night temperatures (170C or less) and when the daylength
was 12 hours or less, Nitsch (1952) found that the proportion of female
flowers rapidly became 100 percent, and the size of the ovaries increased
before full bloom until a parthenocarpic fruit was produced. At different
daylengths, temperatures, and N levels, he found that the largest number
of marketable fruits were produced by plants receiving high N grown under
short day conditions. However, the highest perceItage of marketable fruit
was produced under long day conditions. The highest yields were produced
with high N in the warmer temperature, and neither temperature nor day-
length affected the yield of the low-N plants. It was concluded that N
was the most important factor as far as yield was concerned.

Miller (1957) found that fruits produced under 70°F night temperature
conditions were relatively longer during the harvest period. However, fruits
produced under 60°F conditions were relatively longer during the late harvest
period. Daylength had no effect on length to diameter ratio.

Different light intensities and different levels of 002 also affected the
pickling cucumber fruits. Hopen (1962) reported that larger numbers of
fruit were developed on plants as the light intensity was increased from 300
to 1400 foot candles, and as the 002 concentration was increased from 450
to 1350 ppm. The highest yield was produced at 1400 foot candles of light

and 1350 ppm of 002. Supplemental field lighting resulted in slightly

24

larger fruit yield compared to shaded and natural sunlight conditions.
The importance of N and light was stressed by T iedjens (1928) when
he said: "Even though a certain amount of N is necessary for the growth
of the plant, yet the available sunlight, quantitatively and qualitatively
speaking, seems to be the controlling factor in the abnormal prolificacy
of some Strains of cucumbers and the false parthenocarpic production of
fruits. "
Relationships Between Light Distribution,
Physiology of Plant Growth and Productivity
In the last few years, interest in the analysis of the primary production
of terrestrial and other plant communities has increased. According to
Black (1963), a number of factors has been responsible for this: the clear
understanding of the role of leaf area, following the widespread use of the
concept of Leaf Area Index; the ready availability of measurements of solar
and light energy; quantitative studies of the effects of meteorological factors
on evaporation, and not least, the desire to place the study of yield on a

more exact physiological and ecological basis.

Net Assimilation Rate and Leaf Area Index

 

The concept of net assimilation rate (E) was developed as an aid in the
quantitative analysis of plant growth. According to Briggs _et 31; (1920),

it may be defined as the rate of increase in the dry weight of a plant per

25

unit of leaf area per week. It is given by the equation:

E = W2'W1 x logeLz-logeLl _

 

Lz-Ll t2 -t1

Where: W was the dry weight, L was the leaf area, t was the time and
l was at the beginning and 2 the end of the week. This concept was de-
veloped from the observation that the relative growth rate curve (weekly
percentage increase in dry weight plotted against time), had the similar
form that the leaf area ratio defined as the leaf area per unit dry weight
plotted against time. This similarity suggested that the weekly increase
in dry weight per unit leaf area was more or less constant through the
life cycle.

More recently, Watson (1947) has shown that E varied between different
species grown in thesame environment, between varieties of the same
species, between seasons of the same crop grown in the same place, and
probably with age. The variation of E within and between species, varieties
and seasons was accompanied by relatively greater variations in leaf area.
It was shown that high yielding varieties were those with high mean leaf
areas. There was no association between high E and high yield. Thus,
variation in leaf area was the main factor determining differences in yield.
Dry weitht yield betWeen wheat, barley, sugar beet, and potatoes was
nearly porportional to the integral of Leaf Area Index (L) over the growth
period called Leaf Area Duration (D). Welbank _e_£ a1; (1966) also found a

nearly proportionality of the leaf area duration (D) to yield.

26

From time zero (at germination), Milthorpe (1956) reported the leaf
area index (L) increased very slowly at first and then increased rapidly
to a maximum. This maximum value of L was maintained for a short
time. During the greater part of the life of all crops L was very small
(less than 1.0); in other words, there was insufficient foliage to cover the
soil. This was suggested as one reason for the low efficiency of annual
crops in utilizing solar energy and the most important physiological limita-
tion on dry matter production. Milthorpe (1956) suggested that the main
possibility of increasing yield was in maintaining optimum leaf area index
over a long part of the growth period.

The optimum leaf area index beyond which growth rate decreased

rapidly, have been reported for several crops: 4.5 for Trifdium subter-

 

raneum, (Davidson and Philip, 1958); 3.0 for Brassica oleracea, (Milthorpe,

 

1956); 5.5 for Dactylis glomerata L. , (Pearce e_t al_. , 1963). Pearce g a_l_._

 

(1963) demonstrated that this optimum leaf area index may be governed by
many natural and imposed variables.

Black (1963) shoWed that in T rifolium subterraneum L. and in other

 

crops, the optimum leaf area index was not affected by variations in tem-
perature, but was determined by the incoming radiant energy. The leaf
area index increased as the radiant energy increased. This indicated that
the optimum leaf area index varied seasonably, being higher under high
light intensities of summer than at other times of the year.

Saeki (1960) reported that leaf arrangement and shape could affect the

27

pattern by which light was intercepted and reflected in plant stands. The
mean relative light intensity (I'/Io) at any level of the canopy was determined
by the leaf area index and extinction coefficient characteristic of each plant

community.

Extinction Coefficient (K)

 

As developed by Saeki (1960), the light extinction in a plant community
or the extinction coefficient (K) was determined by three main characteristics:
transmissibility, arrangement and especially inclination of leaves.

The transmissibility of leaves was related to the chlorophyll content per
unit area. According to Kasanaga and Monsi (1954), the logarithm of trans-
mittance decreased linearly with the increase in chlorophyll content. In a
plant community with several planes, therefore, the transmissibility of the
community would be determined by the number and the transmissibility of
each plane. They demonstrated that the photosynthesis under transmitted
light was 70 percent of natural light, and the increased amount of photo-
synthesis in the plant community attained with the transmissibility to a maxi-
mum of 40 percent of the photosynthesis without transmissibility.

Saeki (1960) reported that the mean relative light intensity (I'/lo) pre-
vailing at any level of the plant commtmity was linearly related to leaf area
index. Further theoretical analysis, however, indicated that in a plant com-
munity with steeply inclined leaves, the relation of I'/lo and leaf area index

diverges from perfect linearity. In this case, leaf transmissibility (m) was

28

important and should be included in the equation: l'/Io = exp (-KL)/(1-m).
However, in stands of broad leaves of approximately horizontal habit, the
equation I’/IO = exp (-KL) could be used.

With regard to the vertical distribution of foliage in plant communities,
Saeki (1960) distinguished two major types: a) the herb type and b) the
grass type. In the former the maximum foliage distribution was in the
upper part, while in the latter it was at the lower part. He stated that
this was one of the reasons why the grass plants allowed larger fractions
of light to penetrate into the lower strate of the plant community than did
herbaceous plants. Also, the plant density affected the structural pattern
of foliage in plant communities. In a stand with higher density the whole
foliage was compressed in the upper part while in a stand with lower den-
sity the foliage was distributed more uniformly over a wide range of ver-
tical direction.

Wattson and Witts (1959) studied the inclination of leaves compared
with the productivity in many plant communities. With lower leaf area
indices, daily production in foliage was indifferent to inclination of leaves,
while with increased leaf amount, the role of inclination in the production
became very remarkable, upright leaves (with smaller K) being more
efficient than horizontal ones (with higher K) under full daylight. Wild
sugar beet had leaf photosynthesis rates in spaced stands similar to culti-
vated beet, but under crowded stands was less productive because of the

larger K and more postrate habit.

29

Several investigators have reached similar conclusions regarding the
influence of variations in leaf angle and leaf area index. Loomis and
Williams (1969) found that when leaf area index was small the horizontal
leaves were advantageous. This was especially true in short season crops
where crop yield would be dependent upon the rate at which full cover was
reached, and on the efficiency of the canopy at small values of leaf area
index. At large values of leaf area index, more erect leaves gave greatest
production. However, inclined leaves showed a marked advantage only when
leaf area index exceeded 2 to 4, and erect leaves only when leaf area index
approached high values of 8 or more.

Monsi (1968) reported that the highest productivity was attained in ideal
foliage where light was distributed evenly on every photosynthetic leaf.

Ideal foliage was thought of as a foliage in which the extinction coefficient
(K) changed with depth in the foliage, i.e. K became small near the surface
of the foliage and increased as the amount of light available fell off with

increasing depth.

Photosynthetic Rate, Growth Rate and Productivity

 

Saeki's (1963) studies showed that given the light-response curve of
single leaves in the laboratory, photosynthesis of a stand of the same species
in the field could be estimated when it was known how light distribution be-
low the canopy depended on interception by leaves.

According to Saeki (1960) and Davidson and Philip (1956), laboratory

30

measurements at a: fixed concentration of C02, gave curves for the dependence

of rate of photosynthesis (P) on light intensity (I) fitted by P = {—mfi—L ,
where P was the gross rate of photosynthesis, Pmax was the maximum value
of P attainable (light varying and all other factors constant), k was a constant

(the value of I at which P/Pmax = 1/2), and l was light intensity.

The photosynthetic rate of the cucumber plant (Cucumis sativus "Ohio

 

MR 17") was measured by McCree and Loomis (1969) using the rate of up-
take of C02. In both outdoor and indoor experiments, the exchange rate of
the whole cucumber plant was measured using a transparent plastic chamber
through which air of known 002 concentration was passed at a known rate.
The light-response curve of the cucumber plants, measured in steady light,
had a maximum photosynthetic rate of 29 mg C02/dm2 of leaf surface per
hour, which was reached at 150 W/mz/hour of photosynthetically active
radiation.

According to Davidson and Philip (1956), using the light response curve
of single leaves, and knowing the light penetration at any level of the plant
by the equation: I = 10 exp (-KL) (Beer's Law), the gross rate of photosyn-
thesis could be calculated at any level of the plant by substituting the value
of I (at any level of the plant) in the light response curve:

P = Pmax 10 exp (-KL)
10 exp (-KL) + k
(subject to the condition P = 0, L = 0), gave the gross rate of photosyn-

 

, integrating with respect to Leaf Area Index (L)

thesis of the stand in mg of C02 per dm2 of leaf surface per day,

31

=Pmax ln( Io+k )

P K (Ioexp(-KL)+k)'

 

This mathematical model relating photosynthesis in a crop stand to
horizontal light intensity required a knowledge of the amount of light inter-
cepted by each layer of leaves in order to make integration over all layers
possible. It was assumed that the light at any level was generally pre-
dictable by Beer's Law. Baker and Musgrave (1964), measured the light
interception by a corn stand using two light integrators, one on the ground
and the other at complete exposure, and obtained a very high correlation
between these radiations (measured on a flat horizontal surface) and the
rate of apparent photosynthesis. The response curves could be fitted with
equal precision to either a parabolic regression equation or to the rectan-
gular hyperbolic form used for a single leaf.

McCree and Troughton (1966) reported that, in principle, one could use
the C02-uptake curve to predict growth rate from light. To estimate the
net rate of photosynthesis, the respiration lost must be substracted from
the gross photosynthetic rate. This model assumed that respiration was
proportional to leaf area and independent of growth rate of light level. The
rate of respiration was dependent on light level. Thus, the compensation
point changed according to light intensity. The respiration rates of plants
growing at various light levels were proportional to their photosynthetic
rates. Hence, to their net daily uptake of C02 which was a measure of

growth rate. It seemed entirely reasonable that plants should adapt their

32

respiration rates to be proportional to their growth rates. The idea of a
fixed compensation point has been incorporated into several models. All
assumed that respiration was proportional to leaf area and independent of
light, so that the lower leaves of a dense crop were below their compensa-
tion point and parasitic. McCree and Troughton (1966) indicated that this
change of compensation point according to light intensity suggested that
these models as proposed by De Witt (1959) might be in need of some modi—
fication. Other models did not incorporate a compensation point. They
assumed that the respiration rate was a constant proportion of the rate of
photosynthesis; hence, they subtract 20% from the total gross photosynthesis
of the crop over a long period of time. The De Witt model accurately pre-
dicted the growth rates of plants used by McCree and T roughton (1966).

The generally good agreement between growth rate and daily uptake of
C02 in the experiment reported by McCree (1965) gave an indication of the
validity of the proposed method of predicting growth rate from the C02/

light curves and the light climate.

MATERIALS AND METHOIB

I. Nitrogen Level (Experiment N0. 1)

 

During the summer of 1969 a field study was conducted in order to
determine the effects of N levels and plant populations upon two varieties
of pickling cucumber.

(A) Experimental Design. The statistical design was a split-split
plot using varieties, Pioneer and Spartan Progress, as whole plots, splits
for spacing and these with splits for N. The three spacings utilized were
3" x 5" (11 rows with seed spaced an average of 3" in rows and rows 5"
apart), 5" x 5", and 10" x 5" (6 rows with seed 5" in rows and rows 10"
apart). The levels of N used were 0, 33.5 and 67 pounds of actual N
(as NH4N03, 33.5% N) broadcast at flower initiation (July 28).

All treatments were replicated with 3 plots of each treatment or a total
of 54. The size of each plot was 200 sq. ft. with two additional rows as
borders, and providing enough space between plots (5 ft. at‘the sides and
10 ft. at the end) in order to avoid fertilizer border effect. The plots were
planted June 28 using a Stanhay seeder with belts punched to provide the
theoretical average spacing in the rows using average size cucumber seed.

(B) Soil Type and Analysis. This experiment was conducted on a sandy
loam to loam soil on the Orla Sheathelm farm, 25 miles southeast of Lansing

near Dansville. Based on soil test results from samples submitted to the

33

34

Soil Test Laboratory at Michigan State University, 500 pounds of 8-32-16
fertilizer was broadcast and disc-in prior to planting. The soil had a
pH of 6. 5 and tested 3.6% in organic matter, and 44, 200, 3900, and
450 pounds per acre of available P (Bray P1), K, Ca and Mg, respectively.
Immediately after planting, herbicides were applied using 4 lbs of NPA
(Alanap) and 2 lbs of DNBP (Premerge) per acre (0.2 inch of irrigation was
applied following the herbicide application).

Irrigation was provided using a solid set system (Sequamatic), whereby

approximately 0.2 inch could be applied per day.

(C) Petiole Samples and Nutrient Analysis. Cucumber petiole samples
were collected at two times during the season, just prior to the N applica-
tion and just prior to harvest. Each sample from each plot was composed
of 20 to .30 petioles of living uninjured tissue selected from the middle
portion of randomly selected plants. These samples were stored in the
freezer at -200F for 2-3 months. Tissue samples were analyzed by methods
similar to those outlined by Carolus (1938).

Samples were collected from each plot at harvest, dried, ground and

analyzed by the method outlined by Kenworthy (1967).

II. Irrigation Systems (Experiment No. 2)

 

A second field study during the summer of 1969 was conducted in
order to determine the effects of two systems of irrigation, conventional

and "mist", and plant population upon 3 varieties of pickling cucumber.

35

(A) Experimental Design. The statistical design was a split-split plot
using two systems of irrigation, "mist" (0.04-0.06 inch per hour) and
conventional (0.5 inch per hour). These two main plots were split for
varieties and these with splits for populations. The three varieties utilized
were Pioneer, Spartan Progress and MSU 7006 x 8519 (8821). The spacings
were 3" x 5", 5" x 5", and 10" x 5". All treatments were replicated 3
times giving a total of 64 plots. The size of each plot was 100 sq. ft.
with two additional rows as borders. A distance of 40 feet was provided from
one system of irrigation to the other. The plots were planted July 8 using
a Stanhay seeder with belts punched to provide the theoretical average spacing
in the rows.

The mist irrigation was turned on for about 4-6 hours when the maxi-
mum temperatures during the day reached 83-850F, .as indicated by Carolus
and Van Den Brink (1965). The conventional irrigation was turned on when
the percentage of available soil moisture reached 50% and ran until field

capacity (100% available soil moisture in the first 6 inches) was attained.

(B) Soil Type and Analysis. This experiment was conducted on a
loamy sand at the Horticulture Research Center, 3 miles south of East
Lansing. The soil tested! pH of 5.8, and 6, 16, 600, 1,000 and 180 pounds
per acre of N03, P (Bray P1), K, Ca, and Mg, respectively. The winter
before planting 8-10 tons of manure were applied, and just prior to planting
300 lbs of triple superphosphate were applied due to the low level of avail-

able P reported by the soil analysis. In addition, 30 lbs of N per acre

36

were applied as broadcast when the flowers began to appear. Immediately
after planting, herbicides were applied using 4 lbs of NPA (Alanap) and
2 lbs of DNBP (Premerge) per acre. Soil moisture was adequate to activate

the herbicide.

(C) Soil Moisture Readings. Electrical resistance Delmhorst gypsum
blocks were installed, in pairs at 6" and 12" deep, 10 days after planting.
Each pair was located in plots having different plant population, replicated
twice, and distributed at random within each system of irrigation. The in-
stallation procedure, the reading schedule and the reading conversion were

followed as described by Shearer (1963).

(D) Temperature. Daily minimum and maximum temperatures were
obtained from the meteorological station located at the Horticulture Research

Center. These data are shown in Figure 1.

(E) Precipitation. Daily precipitation was obtained from the meteoro-
logical station located at the Horticulture Research Center. The readings
were obtained at 8:00 a.m. for the 24 hours ending at time of observation.

The data are summarized in Figure 1.

III. Morphological Measurements

 

(A) Internode Length Measurement. Internode length was measured
beginning from the lower part of the plant to the upper part including the

laterals. These measurements were taken at 3 times during the growth

37

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39

period: when the plants developed 5 leaves (June 24), when the plants
started to flower (June 31), and at harvest date, for Experiment 1. Simi-
lar measurements were taken when the plants developed 4 leaves (July 29),
when the plants started to flower (August 7), and one week prior to bar-
vesting (August 15), for Experiment 2. The measurements were taken on

5-10 randomly selected plants for each plot.

(B) Leaf Area Measurements. A method described by Lyon (1948)
was used to obtain the leaf area in the field. This method was based on
the simple mathematical relationship between the overall length (L) of the
leaf and the total area given by the equation: Area = K- L2, where the
factor K varied according with the varieties.

In cucumber leaves, preliminary investigation showed a great variation
according to the size of the leaf, for this reason the equation was modified
to include the width (W) of the leaf. Hence, the area of cucumber leaves
was obtained using the equation: Area = K- L- W.

The factor K was determined for each variety by the following procedure:
the leaf area was determined drawing the leaf on a white paper with a xerox
copier. The paper was cut along the lines and weighed to the nearest 0.001
gun. The area of the leaf was then obtained by dividing the weight of the
paper tracings by the weight of a unit area of the paper. essentially uniform

in thickness. After the areas of 25 leaves of all sizes, the factor K in the
Area
L - W

In the field leaf length and width measurements of all the leaves on

 

equation K = was computed for each of the 25 leaves of each variety.

40

5-10 randomly selected plants were taken from each plot. These measure-
ments were taken at the same time during the growth period as when the
internode length measurements were taken.

(C) Harvest Time Determination. Each plot Was judged ready to
harvest based on the stage of fruit development. A few fruit were allowed
to turn yellow, but the final decision for a given plot was based primarily
on the percentage of grade 2 and 3 cucumbers thought to be present. At
harvest, all the plants from each plot were pulled by hand to get a plant
count, which was used instead of original spacing in further analysis.

(D) Sex Expression. At harvest, 50 plants were selected at random
to determine sex expression. The criteria to determine sex expression
in cucumber plants were based on the terms used by Peterson and Weigle
(1958): gynoecious, in which all flowers were female; monoecious, in which
male and female flowers were born separately on the same plant; and pre-
dominantly female, in which the female nodes outnumbered male nodes by
ratios of 3 or 4 to 1 (reverse ratio to that of monoecious). In most cases
the predominately female bore all its staminate flowers in the first 4 to
8 nodes. Predominantly female plants were classified as gynoecious.

(E) Fruit Grade and Value. The fruits were removed by a stationary
harvester and graded using a standard commercial grader. The following

grades were used and the value assigned to each grade were as follows:

41

Value per bushel
(50 pounds)

No. 1, up to 1 1/16 inch in diameter $ 3.00
No. 2, between 1 1/16 to 1 1/2 inch in diameter 1.50
No. 3, between 1 1/2 to 2 inch in diameter 1.00
No. 4, between 2 to 2 l/4 inch in diameter .50
No. 5, between 2 1/4 to 2 1/2 inch in diameter .25
No. 6, greater than 2 1/2 inch in diameter . 125
Gulls, nubs, all fruits misshapen or un-

desirable $ . 000

IV. Physiological Measurements

 

(A) Total Solar Radiation. Direct and diffuse total solar radiation
measured with a pyrheliometer in gm-cal per cm2 (langleys) on a hori-
zontal surface per hour and per day, was obtained from the station located
at WU'S farm in East Lansing, Michigan. These measurements are

presented in Figure 2.

(B) Light Penetration. Two types of radiation measurement were
needed for ecological studies of plant growth: The absolute intensity on
a horizontal plane above the canopy; and the relative intensities below the
canopy, to be related to the vertical distribution of foliage. These two
measurements were taken for each plot with a Model SR-Spectroradiometer

-2 -l
(ISCO) in microwatts per square centimeter per millimicron (nW cm mu ).

 

 

42

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44

This apparatus met the requirements suggested by Anderson (1964).

In _a plant community, and particularly in a row crop, the horizontal
distribution of radiation may be very irregular. To measure mean
intensity the instrument should either be small enough for easy move-
ment among the plants by hand; or should be large enough to sample

a representative area from a fixed position. Therefore, to obtain re-
presentative light intensity reading within the canopy, a manually movable
sensing head was constructed which allowed several horizontal measure-
ments by sliding the head along at one foot distance. (Figure 3). In all
cases, light was measured in units of energy rate intensity per band
width of each 50 mg in (W cm"2 mu-l within the visible range (400 to
750 mu). A graph of spectral distribution was obtained plotting the light
intensity value for 'each 50 mm wavelength. The area under the curve is

-2
numerically related to the energy available for photosynthesis in uW cm .

(C) Leaf Area Index. The leaf area per plant (mean of 5-10 plants
per plot) was multiplied by the total number of plants of the plot to obtain
the total leaf area of the plot. This value was divided by the area of the
plot to obtain the Leaf Area Index (L). Leaf Area Indices were measured
three times during the growth period and were plotted for each day during

the entire period of growth.

(D) Extinction Coefficient Calculation. The extinction. coefficient (K)

Was computed for each variety and for each plant population using the

45

_—i-”,,._.— - -

-..-..

 

 

Figure. 3. SR-Spectroradiometer (ISCO) with the movable
sensing head used to obtain light intensity (in
“W cm’2 mu- ) above and below the canopy.

46

In IO-ln 11
L

above the canopy, Ii. was the light intensity within the canopy (mean of 6

equation: K = (Saeki, 1959), where 10 was the light intensity

 

measurements) and L was the leaf area index at the time of the light in-
tensity readings. The determination of L was obtained from the curve in

which the leaf area indices were plotted for the entire period of growth.

(E) Photosynthetic Rate Calculations. With the Leaf Area Indices
(L) for each day, the extinction coefficient (K), the solar radiation data (10)
and using the light/photosynthesis curve for pickling cucumber as developed
by McCree and Loomis (1969), the gross photosynthetic rate per day (P) was

, Pmax ln ( Io + k

calculated by the equation: P = T (10 exp (-KL) + k) ; where
Pmax was the maximum photosynthesis, K was the value of irradiance
where P/Pmax was 1/2; both values given by the light/photosynthesis curve
(Figure 4). Since these values (Pmax and k) were expressed in Watts III-2
hr‘l based on irradiance and the values of (lo) given in gram-calories cm‘2

day'l, the necessary transformations were made using Smithsonian Meteoro-

logical Tables (1951).

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RESULTS

I. Relationships Between Cultural Practices and Mogmological Changes

 

in Different Varieties of Pickling Cucumber

 

(A) Internode Length and Number.

Experiment 1. The internode length at three stages of growth of
two varieties, three plant populations, and three levels of N, is graphically
illustrated in Figure 5. The’variety, Spartan Progress, averaged shorter
intemodes than Pioneer throughout the season. The number of intemodes
were not different between varieties. As the plant population increased, the
length of the internode increased (primarily in the lower part of the plant)
and the number decreased. These differences were significant at 1% level
in most cases during the ngth period. Neither N nor the interactions
indicated a significant influence on internode length or number.

Experiment 2. The internode length at three stages of growth of
three varieties, three plant populations, and two systems of irrigation is
graphically illustrated in Figure 6. At first and second observation, the
variety, Spartan Progress, had shorter intemodes than Pioneer and MSU 8821,
but at third observation the variety MSU 8821 had shorter intemodes than the
other two varieties. The number of intemodes was significantly greater in
the varieties, Pioneer andMSU 8821, than Spartan Progress, especially at
the end of the growing period.

The effect of plant population on the internode length and number was

49

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54

very similar to that obtained in the first experiment. As the plant
population increased, the length of the internode increased and the number
decreased significantly.

"Mist" irrigation resulted in a marked influence in the length of inter-
node, increasing it throughout the growing period, but there was no difference
in the number of intemodes, compared with the conventional irrigation.

There was a significant interaction between Spartan Progress and irriga-
tion. This variety had shorter intemodes in conventional irrigation than in
"mist" irrigation, but the reverse occurred with the other two varieties

(Figure 7).

(B) Leaf Area and Leaf Area Index
Experiment 1. Table 1 shows the effect on two varieties of three
levels of N and three plant populations on the area of individual leaves, num-
ber of leaves, leaf area per plant, leaf area per plot, and leaf area index, at
three stages during the growing period. At the beginning of the growing period,
the number of leaves, .leaf area per plot and per plant, and leaf area index
were significantly greater in Spartan Progress than Pioneer.

As the plant population increased the area of individual leaves, the num-
ber of leaves, and the leaf are per plant decreased, but the leaf area per
plot and the leaf area index increased. These differences were significant
throughout the growing season except at the last observation.

Effects of N levels were shown only at the end of the growing period.

As the level of N increased the area of individual leaves, the number of

 

 

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58

leaves, the leaf area per plant, the leaf area per plot and the leaf area
index increased. There were no significant interactions of the main effects
on these characteristics.

Experiment 2. The effect of two systems of irrigation, and three
plant populations on the leaf area of individual leaves, number of leaves per
plant, leaf area per plant, leaf area per plot, and leaf area index throughout
the growing period on three varieties are shown in Table 2.

Mist irrigation resulted in an increase in area of individual leaves,
leaf area per plant and per plot, and the leaf area index. These differences
were significant at 5% level only at the end of the growing period.

Varieties did not differ significantly except for leaf size. However, at
the beginning of the growing period the varieties Pioneer and MSU 8821 had
larger leaves, number of leaves and leaf area per plant than Spartan Progress;
and NBU 8821 had a larger leaf area per plot and leaf area index than Pioneer
and Spartan Progress. At the middle of the growing season the variety, Pioneer,
had larger leaves than either Spartan Progress or the MSU 8821; Pioneer also
had a larger number of leaves and leaf area per plant then Spartan Progress
and MSU 8821; leaf area per plot and leaf area index were higher in Pioneer
and MSU 8821 than Spartan Progress. At the end of the season all values were
greatest for Pioneer and smallest for MSU 8821.

As the plant population increased the leaf size, number of leaves, and
leaf area per plant decreased, but leaf area per plot and leaf area index in-

creased.

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60

There were no significant interactions.

(C) Harvest Date

Experiment 1. The number of days from planting to harvest for
different varieties, plant populations and N levels are shown in Table 3.
The number of days from planting to harvest increased as the plant popu-
lation increased. Also, the variety, Pioneer, matured earlier than Spartan
Progress. N did not influence maturity in this study.

There were no significant interactions.

Experiment 2. The number of days from planting to harvest for
different varieties, systems of irrigation and plant populations are shown
in Table 4. "Mist" irrigation increased the number of days from planting
to harvest. As the plant population increased, the number of days from
planting to harvest increased. The interaction, irrigation x spacing showed
a significant difference at the 5% level, indicating that the number of days
from planting to harvest increased as the plant population increases with
the conventional irrigation, but not with mist irrigation where only the
lowest and highest plant populations were significantly different. The inter-
action, variety x spacing was also significant at 1% level indicating that as
the plant population increased the number of days from planting to harvest
increased in the varieties, MSU 8821 and Spartan Progress, but not in

Pioneer.

Table 3. Number of days from planting to harvest as affected
by variety, plant population and nitrogen level.

 

 

Variety
Pioneer
Spartan Progress
Level of sig.
Plant population
82 , 000
135, 000
188 , 000
Level of sig.
Nitrogen levels
0. 0
33. 5
67. O

Level of sig.

Number of days from
planting to harvest

50. 19
51. 19

(X)

49. 17
50. 89
52. 00

(XX)

50. 56
50. 28
51. 22

 

(x) Significant at 5% level.

(xx) Significant at 1% level.

62

Table 4. Number of days from planting to harvest as affected
by variety, plant population, and system of irrigation.

 

 

Number of days from

System of irrigation planting to harvest
Mist 51. 04
Conventional 50. 4 1
Level of sig. (X)

Variety
Pioneer 50. 72
Spartan Progress 50. 89
MSU 8821 50. 56

Level of sig.

Plant population

117, 000 49. 06
204, 000 51. 11
267, 000 52. 00
Level of sig. (xx)

 

(x) Significant at 5% level.
(xx) Significant at 1% level.

63

(D) Sex Expression

Experiment 1. The effect of different varieties, plant populations
and levels of N on the percentage of gynoecious and monoecious plants is
shown in Table 5. The variety, Pioneer, showed a higher percentage of
gynoecious plants than Spartan Progress, but this difference was not sig-
nificant. As the plant population increased, the percentage of gynoecious
plants decreased significantly. With an increase in N level, there is a
significant increase in the percentage of gynoecious plants. The interactions
of these effects were not significant.

Experiment 2. The effect of irrigation and variety on the percen-
tage of gynoecious and monoecious plants are shown in Table 6. There was
no difference between the effects. of "mist" and conventional irrigation on the
percentage of gynoecious and monecious plants. The varieties, Pioneer and
IVEU 8821, showed a significantly higher percentage of gynoecious plants
than the variety, Spartan Progress. The interaction irrigation x varieties
was significant and shows that with theconventional irrigation, the variety,
Spartan Progress, had a lower percentage of gynoecious plants than the
variety, WU 8821.

The data also show that the variety, WU 8821, had the highest percen-
tage of gynoecious plants with the conventional irrigation. There were no
significant differences with different plant populations.

(E) Fruit Set

Experiment 1. The total number of fruit per plot, the average

64

Table 5. Effect of two varieties, at three plant populations,
and three levels of nitrogen on the percentage of
gynoecious and monoecious plants.

 

 

% Gyno ecious % Monoecious

Varieties
Pioneer 61. 66 38. 34
Spartan Progress 56. 56 43.43
Level of sig.
Plant population
82, 000 65. 51 34. 49
135, 000 59. 24 40. 76
188, 000 52. 58 47. 41
Level of sig. (xx) (xx)
Nitrogen levels
0. 0 54. 86 45. 14
33. 5 61.82 38. 18
67. 0 60. 65 39. 35
Level of sig. (x) (x)

 

(x) Significant at 5% level.
(xx) Significant at 1% level.

65

Table 6. (a) Effect of three varieties and two systems of irrigation, and
(b) effect of three varieties on the percentage of gynoecious and

monoecious plants .

 

 

% Gynoecious

% Monoecious

 

(a) Interaction of irrigation x variety

Irrigation Variety

Mist Pioneer
" Spartan P.
" NBU 8821
Mean

Conventional Pioneer
" Spartan P.
" MSU 8821
Mean

Level of sig.
(b) Variety effect
Pioneer
Spartan P.
MSU 8821

Level of sig.

70.57
61.85
68.27
66.90
66.76
59.78
75.94
67.49

68. 66
60. 81
72. ll

**

29.43
38.15
31.73
33.10
33.24
40.22
24.06
32.51

31. 44
39. 19
27. 90

**

 

(a) *Interactions significant at 5% level.
”Interactions significant at 1% level.

(b) * Significant at 5% level.
“Significant at 1% level.

66

number of total fruits per plant, and the average number of usable fruits
per plant for two varieties in each of three plant populations and three
levels of N are shown in Table 7.

The total number of fruits per plot, the average number of fruits per
plant are a little greater in the variety, Pioneer, than in Spartan Progress,
but this difference was not significant. As the plant population increased,
the total number of fruit per plot increased, but the average number of
total and usable fruits per plant decreased. These differences were sig-
nificant at 1% level.

As the level of N increased, the total number of fruits per plot and the
average number of total and usable fruits per plant increased, but only the
total number of fruits per plot was different significantly at the 5% level.

There were no significant interactions of these effects.

Experiment 2. The total number of fruits per plot, the average
number of total and usable fruits per plant for three varieties each at three
plant populations and two systems of irrigation are shown in Table 8.

The total number of fruits per plot, the average number of total and
usable fruits per plant were a little greater with "mist" irrigation than with
conventional irrigation, but the differences were not significant. The total
number of fruits per plot was highest for the variety, WU 8821, and lowest
for the Pioneer variety. The average number of total fruits per plant was
similar in the three varieties, but the average number of usable fruits per
plant was much higher in the variety, Spartan Progress, than in Pioneer or

WU 8821, but these differences were not significant. The interaction, irrigation

67

Table 7. Total number of fruit per plot, average number of total and
usable fruits per plant for two varieties in each of three
plant populations and three levels of nitrogen.

 

 

Total number Average number Average number

 

fruit /plot total fruit/plant usable fruit/plant
Varieties
Pioneer 450. 3 0. 80 0. 46
Spartan Progress 404.. 8 O. 77 0. 46
Level of Sig.
Plant population
82, 000 399. 3 l. 10 0. 66
135, 000 418. l 0. 70 0. 37
188, 000 465. l 0. 55 0. 31
Level of Sig. (xx) (xx) (xx)
Nitrogen levels
00. 0 377. 4 O. 72 0. 40
33.5 415.2 0.75 0.40
67. 0 489. 9 0. 88 0. 54
Level of Sig. (x)

 

(x) Significant at 5% level.
(xx) Significant at 1% level.

68

Table 8. Total number of fruits per plot, average number of total and
usable fruits per plant for three varieties each at three plant
populations and two systems of irrigation.

 

 

Total number Average number Average number

 

fruit/plot total fruit/plant usable fruit/plant
Irrigation
Mist 450. 2 1. 17 0. 68
Conventional 433. 3 O. 95 0. 60
Level of Sig.
Variety
Pioneer 389. 8 l. 04 0. 56
~ Spartan Progress 444. 9 1. 16 0. 76
MSU 8821 490. 4 0. 98 0. 59
Level of Sig. (x)
Plant population
117, 000 346. 5 1. 32 0. 91
204, 000 445. 7 0. 98 O. 52
267, 000 533. 0 O. 88 O. 49
Level of Sig. (xx) (xx) (xx)

 

(x) Significant at 5% level.
(xx) Significant at 1% level.

69

x variety was not significant.

As plant population increased, the total number of fruits per plot
increased significantly. but the average number of total and usable fruits
per plant showed a sharp decrease.

The interaction of irrigation x plant population was significant at 5%
level indicating that using "mist" irrigation, the number of fruits per plot
was higher at low and medium plant populations, but lower than the con-
ventional irrigation at high plant population.

Also, with "mist" irrigation, it was observed that the average number
of total fruits per plant was greater at the low and medium plant populations,
but the average number of usable fruits per plant was greater only a low
plant population (Figure 8).

The interaction of variety x plant population was significant, which
indicates that with the MSU 8821, the total number of fruits per plot in-
creased significantly as the plant population was increased from a medium
to a high density (Figure 9). With the Pioneer variety, the total number of
fruits per plot increased significantly as the plant population increased from
low to medium density, but showed no further increase at high density.

(F) Yield and Relative Value

Experiment 1. The yield of six grades of cucumbers, percentage
and quantity of nubs, and marketable fruits for each of two varieties in

three plant populations with three levels of N are shown in Table 9.

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Spartan Progress had a significantly greater yield in grades 3 and 4
and a lower yield in grade 6 and fewer nubs than Pioneer.

As the plant p0pu1ation increased, grades 3 and 4 and total usuable yield
showed a slight non-significant increase. The quantity and relative pertent
of nubs was not influenced by plant population. As the N level increased,
grades 3 and 4 and the total and usable yield increased significantly, but
the percentage of nubs was not affected. The interactions of these main
effects were not significant.

The value per acre of six grades of pickling cucumbers and the average
value per bushel for each of two varieties at three plant populations and three
levels of N are shown in Table 10. Neither varieties nor plant populations
influenced dollar value, but as N level increased, dollar value increased
significantly.

The average value per bushel was not influenced by treatment.

Experiment 2. The yield of six grades of cucumbers, percentage
and quantity of nubs, and marketable fruits for each of three varieties at
three plant populations with two systems of irrigation are shown in Table 11.

With "mist" irrigation, higher yield of grade 2 and 3, bushels per acre
and percentage of nubs, and a higher usable yield than with conventional
irrigation was observed.

The variety, MSU 8821, had a significantly greater yield of fruits of

grade 2 and 3 than either the Pioneer or Spartan Progress varieties. and

76

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78

MSU 8821 and Pioneer varieties had a higher yield of grade 4 than Spartan
Progress. The Pioneer variety also had more grade 6 fruit than either

the Spartan Progress or 'MSU 8821 varieties. The percentage of nubs was
lower for the varieties, Pioneer andM'SU 8821 than for Spartan Progress
variety, but this difference was not significant. The total and usable yields
were significantly higher for the variety, MSU 8821, than for Pioneer and
Spartan Progress varieties.

As the population increased, the yield in grade 3 and 4 decreased,
however, the yield and percent of "nubs" and the total bushels per acre in-
creased significantly. Also, as the plant population increased, the number
of usable bushels per acre decreased, but not significantly.

The interaction of irrigation x variety was significant at the 5% level,
indicating that the variety, Spartan Progress, had a lower yield of grade 4
and total and usable bushels per acre than the Pioneer and MSU 8821 varieties
with conventional irrigation than with "mist" irrigation,(T able 11).

The interactions of variety x plant population were significant at either
the l or 5% level, indicating that the variety, WU 8821, had a greater
number of bushels per acre of grade 2 and 3 fruit and total usable yield at
the lowest and highest, but not at the medium, plant populations than either
the Pioneer or Spartan Progress varieties. This interaction is shown in
Figure 10.

The value per acre of six grades of pickling cucumbers, total value per

acre, and average value per bushel for three varieties each at three plant

was. 13.3“ m. ...qu,
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81

populations and with two systems of irrigation are shown in Table 12.

The results for the value per acre of six grades, and the total value per
acre were similar for the interactions and main effect to those of the yield
already explained. The interaction of variety x plant population was sig-
nificant at 1% level, indicating that the variety, NBU 8821, had a higher

total value per acre at the highest plant pdpulation than the Pioneer and

——“—__-tn .A 8
,W' .
p .

Spartan Progress varieties. This difference is shown in Figure 10. The
average value per bushel was significantly higher for the Spartan Progress
variety than for the Pioneer and MSU 8821 varieties.

II. Relationships Between Cultural Practices and Nutrient Composition on

Different Varieties of Pickling Cucumber.

(A) Macronutrients (N, P, K, Ca and Mg). The NO3-N, total N,
soluble P, total P, and K for each of two varieties at three plant populations
and three levels of N, applied when the flowers began to appear, are shown
in Table 13.

Before the application of N, the N03 -N content of the variety, Spartan
Progress, was higher than that in Pioneer. As the plant population increased,
the N03-N content decreased significantly. There were no significant interac-
tions between varieties and plant population. Just prior to harvest, the NO3-N
and total N were both higher in the variety, Pioneer, than in the Spartan
Progress variety. As the plant population increased, total N decreased,
but NO3-N did not show a significant decrease, indicating that as the plant

population increased the response for N increased. As the N level increased,

 

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84

NO3-N and total N increased significantly. There were no significant
interactions between these effects. Before the application of N, the soluble-P
content was inversely related to the NO3-N content.

Just prior to harvest, soluble-P and total P were higher in the variety

TM

....A'. ..
.
'-

Pioneer than Spartan Progress, but the difference was significant at 5%
level only for total P. As the plant population increased, soluble-P and P

decreased. There were no significant effects of N levels on the soluble

wfl‘T" “ "

and total -P content and no significant interactions.
K content in the plants did not show any difference between varieties.
As the plant population increased, the K content increased significantly. As
the N application increased, the K content of the plants increased significantly.
Increase in plant population was associated with a significant increase in

both Ca and Mg, however, with an increase in N, the Ca content decreased.

There were no significant differences in either Ca or Mg contents between
varieties nor significant interactions.

(B) Micronutrients (Mn, Fe, Cu, B, Zn). Mn, Fe, Cu, B, and Zn
values for two varieties each at three plant populations and three levels of
N are shown in Table 14.

There was a difference between the varieties in Cu and Zn. At high
plant populations, the Mn content in the plant was significantly higher.

The interaction of variety x nitrogen was significant at the 5% level
(Table 14), indicating that in the variety, Spartan Progress, the amount of

Zn increased as the N level increased, whereas with the Pioneer variety,

85

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Zn decreased with increased N.

111. Relationships Between Cultural Practices, Light Distribution, Physiology
of Plant Growth, and Productivity in Different Varieties of Pickling
Cucumber.

(A) Light Above (10) and Below (11) the Canopy.

Experiment 1 and 2. A graph of the light spectral distribution within

‘- --Iflu '.' . 3'5 . -m
. I

the visible range, above and below the canopy of a pickling cucumber planting
with a population of 188,000 plants per acre is presented in Figure 11. The
measurements were made on a clear sunny day (August 3) between 10 a.m.
and 2 p. m. at Dansville, Mich. (42 1/2 9 N).

Above the canopy the spectral distribution of the incoming light intensity
showed two peaks: one at 500 ml and the other between 600 and 650 mu.

Below the canopy the spectral distribution of the light intensity showed
two areas of absorption by the plant canopy, between 450 and 500 mu, and
the other between 650 and 700 mu. In both cases, the area under the curve
was used to obtain the light energy intensity above canopy (lo) and below
canopy (Ii)-

(B) Extinction Coefficient

Experiment 1. The extinction coefficient for two varieties each at

three plant populations calculated from I0 and Ii values are given in Table 15.
There were some differences between plant populations within the same variety,

bUt there were no differences between the means of varieties.

87

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89

Table 15. Extinction coefficients calculated for each variety at three plant
populations in Experiment 1 (a) and Experiment 2 (b).

 

 

 

Variety Plant Population/ acre Extinction coefficient (K)*
(a)
Pioneer 197, 000 0. 791* *
Pioneer 142 , 000 1. 157
Pioneer 81, 000 1. 159
Mean 140, 000 . 1. 036
Spartan Progress 179, 000 0. 864
Spartan Progress 128, 000 1. 100
Spartan Progress 83 , 000 1. 196
Mean 130, 000 1. 032
(b) Extinction coefficient (K)***
Pioneer 240, 000 1. 350* *
Pioneer 183 , 000 1. 3 14
Pioneer 99, 000 1. 166
Mean 174, 000 1. 276
Spartan Progress 230, 000 1. 153
Spartan Progress 191, 000 1. 083
Spartan Progress 117, 000 1. 3 12
Mean 180, 000 l. 184
MSU 8821 . 326, 000 1. 499
MSU 8821 ‘ 5‘ 238,000 1.377
MSU 8821 " 136, 000 0. 826
Mean 233 , 000 1. 234

 

 

* Calculate)d from 10 and 11 values obtained on August 3 at Dansville, Mich.
(42 1/2- N) latitude between 10 a.m. and 2 p.m.

** Mean of three replications.

**"‘ Calculated from 10 and 11 values obtained on Au st 5, at the Horticulture
Research Center, East Lansing, Mich. (42 1/2- N) latitude between
10 a.m. and 2 p.m.

90

. Experiment 2. Extinction coefficient for three varieties each one
at three plant populations calculated from 10 and 11 values are given in
Table 15. Again, there was some difference between plant populations
within the same variety, but the difference was small between means of
the varietiees.

In both experiments the extinction coefficient for each variety and for

each plant population was used for further analysis.

(c) Photosynthetic Rate
Experiment 1. Gross photosynthetic rate for two varieties each at
three plant populations and three levels of N, during the period of growth,
is shown in Figures 12,and 13. The area under the curves are shown in
Table 16.

In the varieties, Pioneer and Spartan Progress, the area under the curves
showed great differences among plant populations, a greater area under the
curve in higher plant populations than in lower plant populations. Also, the
area under the curve showed some differences between levels of N within
the same plant population, especially following N application, i. e. July 24
through August 7 for the Pioneer variety at the high plant population.

There was a strong positive correlation (0.9477) between the area under
the curve for two varieties at three plant populations, and total yield.

There was low correlation between the area of the curve and yield for dif-

fe rent N levels.

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95

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96

In some cases the gross photosynthetic rate declined at the end of the
growing period, and was likely associated with an increased percentage of
malformed fruits (nubs) which reduced the dollar value per acre (Table 16).

Experiment 2. Gross photosynthetic rates for three varieties each
at three plant populations, with "mist" and conventional irrigation, during
part of the growing period is shown in Figures 14 and 15. The area under
the curves are shown in Table 17.

The area under the curves, for different varieties at different plant
populations, had a tendency to increase with the "mist" irrigation as com-
pared with conventional irrigation.

In the the three varieties, the area under the curves showed great
differences among plant populations, especially at the beginning of the grow-
ing period, as the plant population increased the area under the curve in-
creased.

There was a positive correlation (0.4939) among the area under the
curves and total yields (Table 17).

As in Experiment 1, it was noted that in some cases the gross photo-
synthetic rate declined at the end of the growth period. This decline in
gross photosynthesis was likely associated with an increase in the percentage

of malformed fruits (nubs) that decreased considerably the dollar value,

Table 17.

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DISCUSSION

It is evident that the cultural and environmental factors studied
influenced growth and development of pickling cucumber) plants. Varieties
showed variable behavior under different practices, which resulted in vari-
ations in yields.

Supporting previous works (Dearborn, 1936; Nitsch, SEE al_. , 1952;

Miller, 1957), N was one of the most important nutritional factors affecting
sex expression, fruiting, and yield of cucumbers. N did not influence

either the length of intemodes or maturity, but influenced leaf area per
plant, sex expression, number of fruit and usable yield. The range of 500
to 700 ppm of N03 -N in cucumber petioles for satisfactory growth (Miller,
1957) was not obtained with the levels of N applied in this. experiment. This
suggested that a higher level of nitrogen application might be used in high
density stands, under the same climatological and soil conditions. As

plant population increased, the need for N apparently increased, but P and

K were probably satisfactory, which suggests that N is the most important
nutrient in cucumber fertilization at high plant populations. The gross photo-
synthetic curve given by the mathematical model presented. showed differences
associated with different N treatments. This suggested that N content and
changes in chlorophyll content stimulated photosynthetic efficiency Re_r_ it:

as previously reported for rice (Murata, 1961) and other crops (Gaastra,

1963; Cowan and Milthorpe, 1968).

102

103

The reduction of plant water stress by the application of "mist"
irrigation during periods of high atmospheric stress have been shown by
Carolus (1969) for several crops and had a direct affect on growth of
cucumber seedlings as indicated by Cuthbert (1966). In this experiment,
"mist" irrigation resulted in an increase in the length of intemodes, leaf
area per plant, number of fruits, usable yield, and dollar value, but de-
layed maturity. "Mist, " compared with conventional irrigation probably
reduced the photosynthetic of midday depression, increasing the gross
(and probably the net) photosynthetic rate of high density cucumber stands.

As plant population increased, important morphological changes occurred
in cucumber plants. In this experiment, with increases in plant population
the internode length increased, but the average area per leaf, the number
of leaves and leaf area per plant decreased; maturity was delayed; average
number of usable and total fruit per plant decreased, total yield per area
. increased but the quantity of usable yield was not influenced.

With a high plant population, the competion for light, with an extinction
coefficient of 1. 0-1.2 and an optimum leaf area index of about 3.5, (in con-
ditions of high light intensity 700 gm-cal cm”2 hour-1) a decrease in the
gross photosynthetic rate at the end of the growing period was caused pri-
marily by an excess of leaf area. This resulted in a significant decrease
in dollar value associated with an increase percentage of malformed fruit.

These results agreed with data obtained by Gilbart (1963) in Cucumis melo.

 

He concluded that leaf area index and photosynthesis during the last two

104

weeks of growth were the most important factors determining fruit size
and quality.

Varieties behave differently under highly competitive conditions in high
plant populations. The variety WU 8821 was apparently more adapted to
high plant populations associated with the following characteristics: shorter
and more intemodes, larger leaves, greater leaf area per plant and a
higher initial leaf area index; but smaller leaves and leaf area, and a lower
leaf area index at the end of the growing period. Also, WU 8821 produced
a higher percentage of gynoecious plants, total number of fruits per plot
(less per plant) with the largest total and usable yeild. The photosynthetic
curve showed a close relationship with the characteristics which increased
photosynthesis at the beginning and at the end of the growing period. These
characteristics were pointed out by Mirthorpe (1956) as most important for
increasing efficiency and production of annual crops.

The morphological and growth characteristics of MSU 8821 suggest a
further study in the architecture of cucumber plants in order to achieve a
more efficient light energy trapping variety that will lead to an increase in
productivity with high plan: populations. Some of these characteristics have
been incorporated into other crops (corn, sugar beet, soybean, rice and
cotton) are shorter intemodes, a change in leaf angle and a change in vertical
distribution of the foliage. Such characteristics which encourage high leaf
area indices and increases the production per unit area, should be pursued

in the cucumber.

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