THE EFFECT OF NITROGEN FORMS AND MEFHODS 0F .

APPLICATION UPON YIELD AND SEVERAL YIELD
. COMPONENTS OF— SOYBEANS
(Glycine max. L)

Thesis for the. Degree of M. S.
, MICHIGAN STATE UNIVERSITY
MANSOOR TASDIGHI
1977

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ABSTRACT
THE EFFECTS OF NITROGEN FORMS AND METHODS OF
APPLICATION UPON YIELD AND SEVERAL YIELD
COMPONENTS OF SOYBEANS
BY

Mansoor Tasdighi

The effects of combined nitrogen on yield and some
other agronomic characteristics were studied on soybean

(Glycine max. L). Soil Applications of calcium nitrate

 

were carried out at weekly intervals. A suppressive
effect of soil nitrogen on the number of nodules per
plant was observed. It was found that yields could be
increased by delaying the application of nitrogen ferti-
lization.

Foliar fertilization using three nitrogen sources,
each at four rates was studied on soybeans. This study
was carried out at the mid-pod fill stage of deve10pment
and showed a negative correlation between yield and rate
of nitrOgen fertilizer. The degree of burning was cor-

related with the solubility and salt index of the

fertilizer.

THE EFFECT OF NITROGEN FORMS AND METHODS OF
APPLICATION UPON YIELD AND SEVERAL YIELD
COMPONENTS OF SOYBEANS

(Glycine max. L.)

BY

Mansoor Tasdighi

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements

for the degree of

MASTER OF SCIENCE
Department of Crops and Soil Sciences

1977

ACKNOWLEDGEMENTS

The author wishes to express deep acknowledgement
to Dr. Taylor J. Johnston who suggested and guided the
current project and generously supplied encouragement
and advice throughout the course of this investigation.
He also wishes to extend acknowledgement to Dr. Everett
H. Everson for his appreciable advice and encouragement
and for reviewing this manuscript.

The author expresses great appreciation to Dr. Charles
E. Cress for his invaluable help in statistical advice
and serving in the guidance committee.

The author wishes to express further acknowledgement
to his family in Iran for their moral support during
his stay in the U.S.A.

The author thanks the students, faculty and staff
of this department who made this period interesting and

rewarding.

ii

TABLE OF

LIST OF TABLES . . . .

LIST OF FIGURES . . . .

INTRODUCTION . . . . .
LITERATURE REVIEW . . .
MATERIALS AND METHODS .
RESULTS AND DISCUSSION

1) Soil practice

CONTENTS

2) Foliar application . . .

CONCLUSIONS . . . . . .

BIBLIOGRAPHY . . . . .

APPENDIX 0 O O O O O 0

iii

Page

iv

15
19
19
38

48

50
S9

LIST OF TABLES

Table Page

1. Yield of soybeans (BU/A) as affected by
time and rate of nitrogen application in
the soil for 1972 . . . . . . . . . . . . . 20

2. Yield of soybeans (BU/A) as affected by
time and rate of nitrogen application in
the soil for 1973 and 1975 . . . . . . . . 22

3. Effect of time and rate of nitroqen applica-
tion in the soil on some agronomic
characteristics of soybeans for 1975 and
1976 . . . . . . . . . . . . (Part 1). . . 25

(Part 2). . . 26

4. Yield of soybeans (BU/A) as affected by the
time and rate of nitrogen application in
the sail for 19 76 O I O O O O O O O O I O O 29

5. Analysis of variance table for soil appli-
cation of calcium nitrate at different times
and rates (Dependent variable is yield) . . 3O

6. Yield of soybeans (BU/A) as affected by the
rate and source of nitrOgen applied as
faliar Spray. I O O I O O O O O O O O O O O 39

7. Analysis of variance table for foliar
application of different sources of nitrogen
(Dependent variable is yield of soybeans) . 39

8. Analysis of variance table for soil appli-

cation of calcium nitrate (Dependent variable
is Yield) 0 O O O O O O O O O O O C O I O O 59

iv

Figure

LIST OF FIGURES

Yield of soybeans (BU/A) as affected by the
time and rate of nitrogen application in the
soil for 1973 and 1975 . . . . . . . . . . .

The number of nodules per soybean plant as
affected by the time and rate of nitrOgen

application in

the soil for 1975 . . . . . .

Number of nodules per soybean plant as
affected by the time and rate of nitrogen

application in

the soil for 1976 . . . . . .

Combined yields of soybeans, for 1973, 75
and 1976 as affected by the time and rate
of nitrogen application in the soil . . . .

Average number
as affected by
application in
1976 . . . . .

Average number
as affected by
application in

Average number

of pods per soybean plant
the time and rate of nitrogen
the soil for 1973, 75 and

of seed per soybean plant
the time and rate of nitrogen
the soil for 1975 and 1976 .

of nodules per soybean plant

for 1975 and 1976 as affected by the time
and rate of nitrogen application in the soil

Page

21

27

31

34

35

36

37

LIST OF FIGURES (cont.)

Figure Page

8. Yield of soybeans as affected by foliar
application of different source of nitrOgen
at different rates . . . . . . . . . . . . . 40

9. Burning effect on soybean foliar caused by
ammonium nitrate at 30 lbs/A . . . . . . . . 42

10. Burning effect on soybean foliage caused
by urea at 30 lbs/A . . . . . . . . . . . . 42

11. Burning effect on soybean foliage caused
by calcium nitrate at 301bs/A . . . . . . . 43

12. Number of pods per soybean plant as affected
by the rates and source of nitrogen by
foliar application . . . . . . . . . . . . . 44

13. Number of seeds per plant of soybeans as
affected by the rates and sources of
nitrogen by foliar application . . . . . . . 45

14. Seed size of soybeans as affected by the
rate and source of nitrogen by foliar
application . . . . . . . . . . . . . . . . 46

15. Number of seeds per soybean plant as affected
by the time and rate of nitroqen application
in the soil for 1976 . . . . . . . . . . . . 61

16. Yield of soybeans for 1973, 1975 and 1976 as
affected by the time of application, in the
soil, averaged over both 45 and 90 pound
rates . . . . . . . . . . . . . . . . . . . 62

vi

INT RODUCTI ON

Soybeans (Glycine max. L. Merr.) like many other
legume plants are able to gain a significant amount of
their nitrogen requirements through the fixation of at-
mospheric nitrogen by specific bacteria that are living
symbiotically in the nodules of their roots. The healthier
and the more the number of the nodules, the greater the
amount of atmospheric nitrogen that is fixed (9). The
number of nodules and the percentage of nitrogen fixed
are influenced by the available calcium in the medium
(3, 12, 13, 32, 35, 43, 61, 64). Smith et a1. (67)
increased soybean yields from 20 - to 35 bu/ac by applying
4 tons of limestone per acre, which raised soil pH from
5.3 to 6.3. Grower, et a1. (17) found that lime, gener-
ally, increased early establishment, seedling vigor, and
subsequent dry matter yield of legumes. Lime is believed
to contribute to the establishment of a proper medium for
activation, survival and multiplication of rhizobia in
sour soils(3, 53, 61, 64, 79).

The ability of the soybean plant (Glycine max. L.
Merr.) to utilize both soil nitroqen (primarily nitrate)
and atmospheric nitrogen has complicated the nitrogen

status of soybeans. When good nodulation is present on

soybean plants, only rarely has the addition of inorgan-
ic fertilizer proven profitable. Perhaps workers have
simply not learned when, how, or what form of nitrogen
to apply without inactivating in part the rhizobium
nitrogen fixing bacteria (9).

Many investigators (16, 18, 20, 27, 33, 57) have
emphasized the importance of some combined nitrogen in
attaining maximum yield. Their yield of soybeans was
closely correlated with the amount of nitrogen accumu—
lated throughout the life cycle of the plant. Grain
yields was determined by the number of pods and subse-
quently by the number of seeds retained by the plant,
and this in turn was determined by the levels of nitrogen
available during the bloom and seed filling periods.

The widely accepted inadequacy of the symbiotic nitrogen
fixation in soybeans for maximum yields, (21, 22, 24,
25, 30, 33, 41, 48, 63, 78), suggests a need for addi—
tional research in nitrogen fertilization of soybeans.
From the many studies conducted, most research workers
agree that symbiotically fixed nitrogen is adequate at
the 20 - bushel per acre level but at the 40 - to 60 -
bushel level, from one - third to as much as one - half

of the nitrogen in the plant comes from the soil in the

form of nitrates and ammonium ions (21, 47, 50). It
has also been clearly shown that as the combined nitrogen
supply increases, the contribution of the symbiotic
bacteria decreases (52, 55, 56). This decrease in effi—
ciency of the bacteria as the combined nitrogen is
increased would suggest that relatively low rates of
nitrogen fertilizer might be quite ineffective (47).

The objectives of this experiment were: (1) to
find a prOper rate, time and form of nitrOgen application
for Optimum yield and number of nodules on soybean roots
(2) to study the effect of soil fertilization with
calcium nitrate on nodulation of soybean plants (3) to
find the effects of foliar application of different

nitrogen fertilizer sources on seed yield of soybeans.

LITERATURE REVIEW

Questions concerning nitrogen fertilization of
soybeans are frequently raised, especially in View of
the present supply of fertilizer nitrogen. Many invest—
igators (29, 51, 52, 55, 56, 60, 62, 65, 66), working
in this area, have proven that combined nitrogen has
negative effects on the number of nodulated roots and
thus on the number of nodules.

To explain the effects of nitrogen compounds on
the nodule formation, several possibilities have been
put forward. Ludwing and Allison (40) propose that
variation in C:N quotient during nitrogen assimilation
is responsible for the change in the reaction of the
legume plant to nodule bacteria. In the presence of low
nitrogen, soybean plants contain an excess of carbohydrate,
some of which is secreted by the roots into the rhizosphere
where it stimulates the growth of micro-organisms (24,
26, 55, 73, 78). But with increasing nitrogen concentra—
tion the plant carbohydrate may be tied up in the protein
forming process to such an extent that there is little
if any carbohydrate excreted from the roots into the

rhizosphere (55). If so, there would be little inducement

for the bacteria to be attracted to the plant roots.

Rovira (59) indicated that during growth stages of
peas actual excretions form the bulk of the material
coming from the roots, and hence must play an important
role in the stimulation of the micro-organisms on and
around the roots. Secretions produced by a particular
legume stimulate multiplication of rhizobial strains
effective for that species more than ineffective ones
or other bacteria (69).

Bacteria secrete materials which may cause root
hairs to curl and become crook shaped, prior to actual
invasion by the bacteria (9). This may be B-indoleacetic
acid (IAA) since pure IAA and filtrates from rhizobia
and other bacteria also induce root hair curling (31,
69). It is also known that IAA may be produced by
rhizobia from tryptophan excreted by the roots. The
curling of root hairs is considered to be the role of
auxin. Auxin may also play an important role in the
growth of infection threads* and the initiation of the
cell division leading to nodule formation. Tanner (70)
proposes that the effect of combined nitrogen on nodula-
tion is due to a reduction of auxin concentration in the

rhizospher.

Using strains of Rhizobium meliloti; B. trifolii,

 

and B. japonicum, it has been shown that nitrate is

 

reduced to nitrite which inactivates IAA, but that the
presence of NH4++ inhibits the conversion of tryptophan
to IAA (70).

Once root hair curling occurs, the host produces
extracellularly the enzyme pectinase in response to a
stimulus caused by specific rhizobia. Ljunggren (36),
in an extensive study, indicated that pectinase activity
is influenced by the presence of calcium. It was sus-
pected that the decreased enzyme activities with
increasing nitrate concentrations might be due to an
ion exchange resulting in Ca++ leakage from the roots
into the medium. In this relation, Loneragan (37)
suggested that there is a calcium shortage in the host
plant. It is evident from Ljunggren's studies that there
is a close association between pectinase production and

nodulation. The retarding or inhibiting effect of

 

* Threads are formed by the cytoplasm of the host cell
and is a thin, continuous line of Rhizobia inbedded in

baterial slime (9, 82).

absorbable nitrogen on nodulation works through a delayed
or prevented production of pectinase.

It has been shown that prevention of nodulation is
reached only above certain soil nitrogen concentration
levels. Early supplies with small amounts of mineral
nitrogen enable the plant to maintain a reasonable
growth rate from the outset. This may cause more rapid
plant growth and root development which would then
prepare more sites for nodule production (4, 24, 25, 52,
62, 73).

There are a considerable number of literature
reviews (i.e. 21, 22, 24, 25, 33, 38, 78) on behalf of
inadequacy of nitrogen fixation by the rhizobia living
symbiotically on a soybean plant's roots to meet the
needs of the plant. Nodulated sobyeans do not make
maximum dry weight yields when relying throughout the
life cycle predominantly on nitrogen fixation to supply
total nitrogen needs of the plant (48). In field
experiments carried out by Kang (30), fixed nitrogen was
adequate to supply the nitrogen needs of the crop, but
30 Kg N/ha was needed with inoculation for maximum yields.
Increased yields and higher content of total nitrOgen

fertilizer have significantly outyielded those not supplied

additional available nitrogen (24).

The time of applying nitrogen fertilizer is of con—
siderable importance. Many researchers (22, 24, 63)
have emphasized the requirement of an adequate nitroqen,
supply at early stages of growth for superior vegetative
growth. Availability of mineral nitrogen at the full-
bloom growth stage is critical (21, 63). Much nitrogen
is needed at this stage for duplication of both genetic
and protoplasmic proteins. Shibles and Weber (63)
indicate that if nitrogen is limiting at full-bloom or
pod and seed setting, abortion of potential storage
sites occurs. During bean filling, nitrogen is needed
for production of storage proteins.

There is some evidence that nitrogen added below
the nodule zone may inhibit nitrogen fixation less than
nitrogen applied in the nodule zone. Van Schreven (73);
Harper and Cooper (23); and Criswell et a1. (10),
individually have shown that leghemoglobin levels are
reduced less when nitrogen was supplied deep within the
root zone. Nodular development and nodule number are
inhibited less when nitrogen was placed below the
primary zone of nodulation.

The less mobile forms of mineral nitrogen have less

retarding effects on nodulation. Allos and Bartholomew
(4) have concluded that, in general, the greater the
total and attentive immobilization of nitrOgen, the
larger the fixation. Tanner (70) has concluded that
the nitrate forms Of combined nitrogen are less suppres-
sive than other forms of nitrogen fertilizer.

As mentioned earlier, calcium plays some physio—
logical roles in favoring nodulation and its effects
are local or restricted in increasing the number of root
infections (3). Several investigators (61, 64, 74)
believe that the influence of calcium toward increasing
nodulation is one of keeping the bacteria viable and
infective during a long period of time. Albrecht and
Davis (3); Loose and Louw (38); and White (79), are
of the opinion that the effect of calcium is not necessar-
ily one of keeping alive the bacteria applied as inoculant
since liming increases the number of nodules caused by
organisms originally present in the soil. In the
absence of clacium, bacteria develop chromogenic forms
which will not form nodules on legumes (43). With the
addition of calcium, these revert to non-chromogenic
forms which nodulate the host legume normally.

It has been observed by many researchers (i.e. 2,

10

46, 64, 68, 79) that calcium and hydrogen ions intereacted
on nodulation. In the studies of Albrecht (2) no
nodules were produced by the soybean plants at pH 5.0

or lower. In soils with a pH lower than 5.0, the
nodulation failure was brought about not so much by the
degree of acidity as by the deficiency of the available
calcium in the soil. This emphasized the need for
consideration of fertilizing with calcium on the less
acid soils as well as changing the reaction in those

of higher degrees of acidity, if soybeans and possibly
other legume crOps are to grow well and to be thoroughly
inoculated. In this relation, Spencer (68) proposed a
combination of both these factors for maximum nodulation,
since neither increased pH nor increased calcium supply
alone markedly improved nodulation. In addition, Munns
(46) has declared that increasing soil aciity increased
the calcium concentration needed to achieve better
nodulation. Further, Albrecht (1) pointed out clearly
that the significance of calcium for the soybean plants
rests on its function as an element in the plants'
activities rather than on that of reducing hydrogen ion
concentrations of the soil or growth medium.

The calcium supply must first meet the requirements

11

for growth and then an additional amount of this element
is needed to permit nodule formation. It has been
pointed out from previous works (i.e. 3, 28, 37, 74, 75,
76, 77) that the cell walls of calcium-deficient seed-
lings fail to retain their shape. Almost all of the
calcium of deficient cells is located in the wall
fraction. There is markedly swollen conditions, the
results from.the omission of calcium, which is found to
lie associated with marked vacuolation. Vacuolation
suggests the liklihood that the cell wall has lost its
normal rigidity and has permitted extra water to be
taken in.

The more soluble forms of calcium appear to be
more effective, since the use of calcium by Scanlan (61)
both in the form of calcium chloride and calcium nitrate,
gave significant increases in nodulation when compared
to calcium acetate and calcium carbonate supplemented
with acid phosphate. Both of these forms of calcium,
when used on soybeans, not only increased nodulation
but also increased the percentage of plants having nodules
on their roots. Because of the immobility of calcium
within the plant a constant supply of this element is

required by the soybeans (49).

12

During recent years, the practice of applying
fertilizer solutions directly to the foliage of agri-
cultural plants has received increasing attention. A
number of crops have responded well to this method of
fertilization, while others have shown no significant
effect on yields or are severely damaged by even small
applications of fertilizer solutions (15, 45).

The success of minor elements in foliar sprays
encouraged investigators to try to supplement or replace
soil applications with macronutrient elements (8).
Mederski et a1. (44), in the studies with six important
field crops over a period of three years, concluded that
the applications of complete foliar sprays did not serve
as an effective supplement to or as a substitute for
conventional soil fertilization practices. Later on,
Rajan et a1. (54), in a review of recent works on foliar
application of plant nutrients to crops, concluded that
the same rate of fertilizer gives greater increase in
crop yields when applied as a foliar spray than when
applied to the soil. The effectiveness of fertilizers
is conditioned by the rate of uptake and subsequent
mobility of the nutrients often is more beneficial when

applied as a supplement to rather than as a substitute

13

for soil application of fertilizers (54).

In most recent years, the studies of many research-
ers (5, 14, 58, 71) have shown promising results for
foliar application of macronutrient elements on different
crops. Most of the positive responses were obtained
when nutrients were sprayed throughout the fruit setting
and seed filling periods. Roman Garcia and Hanway (58)
postulate that the uptake of nutrients from the soil
and their rate of translocation through the xylem is
not adequate to supply the requirements of the soybean
plants and avoid the normally observed depletion of
macronutrients (e.g. N, P, K, and S) from the leaves
during the seed filling period.

Theoretically, foliar feeding of plants has many
advantages over the conventional method of nutrient
uptake from the soil (80). The ease of application;
the more accurate and precise control of the nutrient
levels of plants; and the greater availability of nutrients
are advantages. Also, leaf feeding apparently eliminates
many difficulties of soil fertization, such as, fixation,
leaching, undesirable pH, limited moisture supply, and
nutrient antagonisms. Other advantages which may be
credited to foliar feeding are, the economy of fertilizer

usage, avoidance of mechanical injury to the roots, and

14

the possibility of the intake of nutrients through the
leaves without being affected by low temperatures to

the same extent as in absorption by roots. All minerals
when Sprayed unappropriately caused more or less burn-
ing on foliage. Lucas (39) suggests fertilizers can
show differences in burn which are measured by a "salt
index". This index is compared against an equal weight
of sodium nitrate. The salt index for some common

fertilizers:

 

Salt Salt index*
Potassium chloride 116
ammonium nitrate 105
sodium.nitrate 100
Urea 75
Potassium nitrate 74
Ammonium sulfate 69
Calcium nitrate 65
Potassium sulfate 46
Super phosphate (0-46-0) lO
Mono potassium phosphate 8
Gypsum 8
Limestone 5

* From Rader et a1., soil Science 55-201—218.

MATERIALS AND METHODS

Field studies were conducted at the CrOps Science
Research Farm of Michigan State University (CSRF-MSU)
at East Lansing, Michigan, on fine sandy loam soil with
a pH of 6.0 during 1972 - 1976. A.well-adapted variety,
"Hark” in Maturity Group I, was used. Plots were not
irrigated.

Preliminary studies in 1972 included rates of 25
and 50 pounds of nitrogen per acre in the form of calcium
nitrate (15.5% N) applied at planting or at 3, 6, 9 or
12 weeks after planting. A check plot with no nitrOgen
application was included in a randomized complete block
design with three replications. During the growing
seasons of 1973 - 1976, the previous studies were improved
to weekly intervals and the rates of applications were
changed to 45 and 90 pounds per acre of calcium nitrate
fertilizer. The times of application began three weeks
after planting and ended ten weeks after planting,
resulting in ten treatments for each of application rate
as follows: check, at planting time 3, 4, 5, 6, 7, 8,

9 and 10 weeks after planting.

The variables were arranged in three replications

15

16

of a split plot design with rates as the main plots and
times of applications as the sub-plots during the studies
from 1973 to 1976.

The seeding rate resulted in approximately 15 plants
per meter of row in rows 75 cm apart in all years and
locations. Each plot was 6.1 meter long and four rows
wide. The calcium nitrate fertilizer was applied as a
side dressing, 5 cm from each row with a Planet Junior
machine. Adequate phosphorus and potassium (250 pounds
per acre of 0—26—26 fertilizer) were added at planting
time to all plots each year.

In 1976, adjacent soybean plots of the same variety
received one foliar application of fertilizer nitrogen
at the early pod-fill stage, when the lower pods were
just beginning to fill. This study wasgconducted at
CSRF-MSU, in support of the soil fertilization practice.
Calcium nitrate, Ammonium nitrate, and Urea solutions
were Sprayed, each at rates of 10, 20, 30 or 40 pounds
per acre, on the leaves of soybean plants in 24 gallons
of water per acre, with a Hudson backpack sprayer
equipped with a constant pressure control valve. This
study was in a completely randomized design with three

replications.

17

One week after the last calcium nitrate applica-
tion, data to determine the effect of soil nitrogen on
nodulation were taken for each treatment. This was
done by lifting out one-half meter of the row, washing
the soil from the roots and counting the number of
nodules. These values were then converted to the number
of nodules per plant.

Some other yield components, such as number of
pods, seeds, and branches per plant, number of seed per
pod and seed size, were measured one week prior to
harvesting. These data were taken for each treatment
by cutting the plants just above the soil surface in
one-half meter of the row and counting the number of
pods, branches and seeds. These values were then converted
to the number of pods, seeds and branches per plant and
number of seeds per pod. A measure of seed size was
obtained by weighing one hundred seeds for each treat-
ment. The plants from one-half meter of the row of
foliar practice were cut into three equal sections, top,
middle and bottom and the same data as above were taken
for each section.

The seed yield data for both soil and foliar

practices were taken by harvesting 5 meters of the center

18

two rows of each plots. Harvested seeds were dried to
a uniform moisture, weighed and recorded as bushels of

soybeans seeds per acre.

RESULTS AND DISCUSSION

1) Soil practice:

Results of the 1972 experiment are presented in
Table 1 and show a 14.7% yield increase (5.6 BU/A) when
50 pounds of actual nitrogen were applied per acre
three weeks after planting when compared to the check
plot yield. The six week application increased yields
5.1 bushels per acre, a 13.4% increase.

Because of the similarity of yields of the three
and six week applications, the treatments were increased
to weekly intervals in 1973 to see if a yield peak had
been missed in 1972. Figure l and Table 2 show yield
results for 1973 and 1975. The 25 pound rate did not
give statistically significant yield increases in 1972
so the rates were changed to 45 and 90 pounds calcium
nitrate per acre. Although not statistically significant
all times, except 3-week, applications at the 90 pound
rate gave some increase in yield over the check plots
in 1973. For both rates, highest yields were obtained
from nitrOgen application at either six weeks or seven
weeks after planting in 1973. Figure 1 shows a striking

resemblance between the 1973 and 1975 yield reaponse

19

 

Table 1... Yield of soybeans (BU/A) as affected by Time

and Rate of Nitroqen Application in the Soil

for 1972

20

 

Treatment time 25 lbs N/A 50 lbs NZA
Check (no nitrogen) 38.8 38.0
0 week (planting) 41.1 41.8
3 weeks 40.4 43.6
6 weeks 38.2 43.1
9 weeks 40.1 40.5
12 weeks 39.2 42.2

 

 

21

52
o
C
O ./ \./ \
50 \ / I.--“ .f.
or. / .\
.Ick \/ I
\ l
461 /
L
A
O ’ \ I ‘
44-‘---"-—-_"’ \ I \‘ ‘
\ I
\ I \
42 \‘,”:\\\ \/‘\\\
‘/\\ A
4* \

Yield (BU/A)
w w I‘
m a: o
I-Ij:::::::;;:llll
\'
.’
I
I
I
l> o '.
I
I
I
.

1973
. 1975
34 4"”
—-- 45 lbs N/A
' 90 lbs N/A
I
o 3 4 5 6 7 e 9 10

TIME (weeks after planting

Figure 1... Yield of Soybeans (BU/A) as Affected by the Time
and Rate of Nitrogen Application in the Soil for
1973 and 1975.

22

Table 2... Yield of Soybeans (BU/A) as Affected by Time
and Rate of Nitrogen Application in the Soil
for 1973 and 1975

 

 

- “5”” N“ W M
Treatment Time s s
Check (no N) 47.5 43.7 47.1 36.3 45.6 47.1
0 week(planting) 47.5 44.1 50.7 37.9 45.8 44.3
3 weeks 49.0 43.6 44.2 33.8 46.3 39.0
4 weeks 45.4 44.7 47.4 34.1 45.1 40.8
5 weeks 47.8 41.5 50.1 39.2 44.7 44.7
6 weéks 48.4 42.2 51.2 42.1 45.3 46.7
7 weeks 49.4 45.0 50.1 40.8 47.2 45.5
8 weeks 49.0 38.7 50.9 41.9 43.9 46.4
9 weeks 48.0 38.5 49.1 41.0 43.3 45.1
10 weeks 47.1 37.1 49.2 44.0 42.1 46.6

 

 

23

carried for the 90 pound rate, and even though an explan-
ation is not readily obvious, yields were lowered with
the application of 90 pounds of nitrogen three weeks
after planting as compared to yields when nitrogen was
applied at planting. Although statistically significant
only at the 10% level due to variability in results, the
1975 data do show some interesting interactions between
time and rate of application (Figure l). The only yields
greater than 40 bushels per acre were obtained when
nitrogen application was delayed until at least six weeks
after planting at the 90 pound rate.

The 1974 experiment was identical to that of 1973,
but a severe drought and lack of irrigation capability
caused yields to be extremely low and results highly
variable. Consequently, results from 1974 are not in-
cluded.

In 1975 and 1976 additional data related to the
number of nodules per plant, number of seed retained
per plant and the number of seeds filled per pod, were
recorded for each treatment (Table 3). Although an
early frost influenced the final yield results for 1975
(Figure l), the nodulation data, shown in Figure 2,

support the original hypothesis that if nitrogen applica—

24

tion is delayed until after nodulation occurs, soybean
plants may receive nitrogen from.both the inorganic
source and symbiotic source.

It is obvious from Figure 2 that as we delayed
application of the calcium nitrate more nodules formed
on the roots of soybean plants in 1975. The weather
information may explain the sharp decline in the number
of nodules formed per plant when nitrOgen fertilizer
was applied seven weeks after planting. At the time
of application the soil was well moistened and shortly
after application a light rainfall (5.25 mm) contributed
to a very favorable situation for the roots to uptake
available fertilizer nitrogen in the soil medium.

The yield responses for years 1973 and 1975 are
highly significant due to the mentioned early frost in
1975 growing season. This is shown in Figure 1. This
figure exhibits a harmonical yield response to the times
of calcium nitrate application for 1973 and 1975. As
can be seen, yields dropped when calcium nitrate was
applied three weeks after planting in contrasts to that
of planting time and gradually increased until seven
or eight weeks after planting. According to the defini-'

tion of Carlson (see reference 9), the drop in yield in

25

Table 3(Part 1)... Effect of Time and Rate of Nitrogen

Application in the Soil on some Agronomic

Characteristics of Soybeans for 1975 and 1976

 

 

 

qum I II
enmmnI momm\pwmsfi mambovmm\ mommm\ppmon momm\pom onw§m\woo
Show Imebn moon
am we em mo em mo am mo em mo
nmwnmaso 2v mo.m qw.H w.H w.e Huw.< Hwy.» ~.c ~.H Hm.o Hm.u
0 Snow
prmbdwbmv ma.H uw.o w.H m.» ku.m Hew.m ~.H ~.o Hm.o Hm.o
w tmmxm q~.q mm.w ~.m w.u Hmm.w Hua.u N.» ~.o Hm.m Hm.m
a sworn m~.~ mm.o ~.m w.m Hum.m Hau.m ~.~ ~.H Hm.o Hq.o
m Sworn eq.w em.» ~.m ~.m Ho~.o mm.m N.» ~.o Hm.o Hm.w
m Sworn mm.m mH.o w.m u.» me.m ppm.m ~.H H.m Hm.o H<.~
q Sworn mH.H mo.» ~.m w.o Hua.m Hum.m N.o N.~ Hm.o Hm.q
m Sworn um.o qm.m w.» e.» Hmo.o Hmu.m N.o H.m Hm.o Hm.m
m Sworn mH.o mm.m w.m a.q qu.q mum.» N.H ~.o Hm.w Hm.o
Ho sworn mm.q mm.m ~.m ~.m Hep.w Hm~.m ~.o ~.m Hw.m Hq.o

C

 

26

Table 3(Part 2)... Effect of Time and Rate of Nitrogen

Application in the Soil on Some Agrono

Characteristics of Soybeans for 1975 and 1976

 

ImmmmIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
enmmnI womm\pwmsn mebosmm\ moomm\pwmbn moma\pom nnmam\woo
soon

(wwmbn moon
pm we mm, mo em mo em no am no
nmmnxaso zv mo.u w.» u.» HNm.H Hwo.w N.H N.» Hm.m Hm.H
o zmmw
Appmsnwamv mm.m u.m .u.q Hwy.» Hmm.o ».q ».w Hm.o Hm.o
u sworn mw.m ».w N.» Hom.m Hom.m ».o ».o Hm.m pm.»
A sworn mm.u s.o w.o qu.m HHo.m ».H ».o Hm.o Hm.w
m £mme ma.w w.» ».m HNHIN Hom.m N.» N.H Hm.» Hm.w
a sworn em.w w.o w.» Hou.e qu.o N.» ».H pm.» ya.»
u zmmxm q».o A.» ».m was.» HHm.e N.» N.u Hm.w Hm.»
m zmmwm as.» w.» w.H Hum.s HNH.o N.» N.m Hm.m Hm.m
m zmmwm ee.u ».m u.w my.» Hmo.m N.H ».m Hm.m Hm.m
Ho sworn mm.» u.» w.m HNw.H ppm.w N.» N.H Hm.w Hm.o

# Nodules/plant

27

140

130

120

IDIh-Ini-IIIiI-L
‘I
1
I.

110

100

90

8O

 

--... 45 lbs N/A
--- 90 lbs N/A

 

0 3 4 5 6 7 8 9 10
TIME (weeks after planting)

Figure 2... The Number of Nodules per Soybean Plant as Affected
by the Time and Rate of Nitrogen Application in the
Soil for 1975

28

the third week application might be due to the retarda-
tion of aImajor part of the nodules which usually form
from two to four weeks after planting. Although not
statistically significant, the time and rate of calcium
nitrate application had some effect on several other
agronomic characteristics which affect yields (Table 3).

The number of branches produced per plant and the
number of pods retained by the plant increased when the
application of calcium nitrate was delayed until nine
weeks after planting.

Yield data for 1976 are presented in Table 4. The
time of calcium nitrate application had a highly signi-
ficant effect on the yield response. (Table 5).

The reason for the yield decline at the nine week's
application time is not obviously clear but soil moisture
conditions before and after application may offer one
explanation. At the time of application the soil was
very dry and information from the United States Weather
Service showed that precipitation sufficient to moisten
the soil did not occur. The 90 pound rate gave higher
yields than the 45 pound rate when nitrogen application
was delayed until eight weeks after planting. The

nodulation data (Figure 3) showed that the number of

29

Table 4... Yield of Soybeans (BU/A) as Affected by the

Time and Rate of Nitrogen Application in the

Soil for 1976

 

 

71976‘FF Ave.—I5?‘1973:75:—-
1976*
Treatment time 45IE§_N7AF95I5§—N7A s N A s N A
Check(no N) 43.22 40.71 44.76a 41.35f
o week(Planting) 43.43 43.11 45.00a 43.90def
3 weeks 45.22 44.33 45.93a 40.80f
4 weeks 42.50 45.11 44.20ab 42.20ef
5 weeks 46.44 44.54 45.25a 44.61de
6 weeks 44.68 47.16 45.108 46.80d
7 weeks 44.43 43.39 46.30a 44.78de
a weeks 47.51 47.48 45.10a 46.76d
9 weeks 36.26 43.54 40.92bc 44.57de
10 weeks 40.63 41.72 41.63c 44.95de

*Means in a column with the same letter are not significantly

different from each other with LSD at k = 0.10.

30

Table 5... Analysis of Variance Table for soil Application
of Calcium Nitrate at Different Times and

Rates (Dependent Variable is yield).

 

 

 

 

 

 

I
Source of variance S.S df MS F
Rep 100.00 2 50.00 2.014
Rate 6.85 l 6.85 0.276
Error (a) 49.63 2 24.81
Time 286.36 9 31.82 3.423**
Rate x Time I 111.69 9 12.41 1.335
Error (b) 334.60 36 9.29
Total 889.13 59 J

 

31
18

7
170 ,
16 I

15 I

13

H
H

 

 

 

JJ
5
'3.
\~10 ’ \\ I 0
\
a
'8 9 ‘J
n
*-
8
O
70
. "'""' 90 lbs N/A
. 45 lb! N/A
0 3 4 S 6 7 8 9 10

TIME (weeks after planting)

Figure 3... Number of Nodules per Soybean Plant as Affected by the
Time and Rate of Nitrogen Application in the soil for
1976

32

nodules decreased when 45 pounds of nitrogen was applied
any time before the eight weeks date when compared to
the planting date application. Although not statistically
significant, the number of nodules formed when either
45 or 90 pounds of nitrogen was added at planting was
greater than the nodules produced on the check plants.
This is in agreement with the findings of Carlson (9),
that an initial supply of nitrOgen is favorable for
nodule formation on soybeans. The number of nodules
per plant for 1976 was relatively higher than in 1975
and also nodulation response to the time of calcium
nitrate applications was much more variable. These
variations might have been due to the organic residuals
from the previous crop in the field. Sugarbeets were
grown in the field in 1975 and this might have increased
the C/N ratio of the soil which would create more favor-
able conditions for nodulation and may interact with the
suppressive effect of mineral nitrOgen on nodule formation
and activities.

The combined results of yield for three years
(1973, 1975, 1976) are also presented in Table 4 and
show that the highest yields were obtained when the appli-

cation of calcium nitrate was delayed until six to eight

33

weeks after planting at either 45 or 90 pound rate. The
same data are graphed in Figure 4 and again it appeared
that the soybean plant can show a positive response to
the combined mineral and organic nitrogen added later
in the growing season. This is due to the high demand
for nitrogen at the reproductive stage in which the
symbiotic nitrogen is normally the major source. This
holds true for the number of pods retained and the number
of seed which produced by single plants (Figures 5 and
6). The three-year average in Figure 4 also shows that,
beginning about 5 weeks after planting, the 90 pound
rate gave the greater average yield response, indicating
the ability of the soybean plant to utilize fairly large
amounts of nitrogen during the reproductive stages of
development.

The combined nodulation data for 1975 and 1976
are presented in Figure 7. The number of nodules
increased when calcium nitrate was applied later in the
growing season. As might be expected, the retardation
effect of nitrogen on nodulation at the 90 pound rate was
higher than that for the 45 pound rate when applied late

in the growing season.

34

47
O
\ '~ /
46 ’,-‘ I/ \
as,” \ /’\/ \\
’l \ 0---. .
44' \ ’ 0
| \ I / O ‘ ./
\I \
. \
43,0. \
l\ I
43.ck \

Yield (BU/A)
h .5
I-'
O
\
\
\
\
O

 

 

I ---45 lbs N/A
| 90 lbs N/A
0 3 4 5 6 7 8 9 10

TIME (weeks after planting)

Figure 4... Combined Yields of Soybeans, for 1973, 75 and 1976 as
Affected by the Time and Rate of Nitrage Application
in the soil.

35

4 pods/plant

45 lbs N/A

--- 90 lbs N/a

0 3 4 5 6 7 8 9 10
TIME (weeks after planting)
Figure 5... Average Number of Pods per Soybean Plant as Affected

by the Time and Rate of Nitrogen Application in the
Soil for 1973, 75, and 1976.

36

140 " 0
I \ ,
I \
' \\ ” \\
i \ I’ \
\, \
120 I e \
I \
I \
\
110 l’ .
\ I
\\l ‘
100 :/

90

80

#seeds/Plant

_..._ 45 lbs N/A
..__.. 90 lbs N/A

 

O 3 4 5 6 7 8 9 10
TIME (weeks after planting)
Figure 6... Average Number of Seeds per Soybean Plant as Affected

by the Time and Rate of Nitrogen Application in the
soil for 1975 and 1976.

37

150
140
130
120 . I
'Dck 0 ; '
I
I C
e I
. \ I
C
I
e
I

100 ’p."‘—.

80

# Nodules/Plant

"‘ 45 lbs N/A
--' 90 lbs N/A

4 5 6 7 8 9 10
TIME (weeks after planting)

O
b)

Figure 7... Average Number of Nodules per Soybean Plant for 1975
and 1976 as Affected by the time and rate of Nitrogen
Application in the soil.

38

2) Foliar application:

Table 6 represents yield data for foliar applica-
tion of three different sources of nitrogen each at
four rates of application.

The sources of nitroqen did not show any statisti-
cally significant effects on the yield but the effects
of rate of application were significant (Table 7). At
10 pounds per acre all nitrogen sources slightly increased
the yield (Figure 8). The small difference in the yield
response to the source of nitrogen might be due to the
degree of solubility in the water and/or absorbability
by the leaves. At the 20 pound rate, Urea slightly
increased yield of soybeans but at higher rates it caused
a steady reduction in yield which was probably due to
salt toxicity and obvious leaf burning by urea at the
higher rates. Calcium nitrate reduced yield at the 20
pound rate but showed no additional decrease in yields
at the higher rates. The lack of yield response to
calcium nitrate at the rates higher than the 20 pound is
probably due to low solubility in the water and subse-
quently inefficient absorbtion of this fertilizer by
leaves. However, the yields of soybean were higher at

30 and 40 pound rates with calcium nitrate rather than

39

Table 6... Yield of Soybeans (BU/A)* as Affected by The

Rate and Source of NitrOgen Applies as Foliar

 

 

Spray

Treatment

Rate Ca(N03)2 NH4NO3 Urea
Check 40.70 40.70 40.70
10 lbs N/A 41.24 42.82 41.60
20 lbs N/A 38.10 40.17 41.89
30 lbs N/A 38.70 37.45 37.76
40 lbs N/A 38.02 31.50 36801

* Values in a column with the same letter are not signi-
ficantly different from each other at c = .05 by LSD
method.

Table 7... Analysis of Variance Table for Foliar Applica-
tion of different sources of Nitrogen (dependent

variable is yield of soybeans)

 

Sources of variance S.S. d.f. MS _F_
Rate 224.22 3 74.74 6.32*
Treatment 11.74 2 5.87 0.50

Rate x treat 83.52 6 13.92 1.18

Error 283.58 24 11.82

Total 603.07 25

 

43 ‘
42
.‘fl_ ___.-I
e
41
ck
40 7
39
/O
33 O \\ \.
I
A
37
36 I
35
34
‘12
B
m 33
"O
'3
oH 32
>4
A
31
30 e Ca(NO3)2
I ‘ NH4NO3
i I Urea
10 20 30 40

RATE (lbs N/A)

Figure 3... Yield of Soybeans as Affected by Foliar Application of
Different Sources of Nitrogen at Different Rates.

41

with urea or ammonium nitrate which may be due to higher
salt index and burning effect of urea and ammonium ni-
trate.

The yield responses of soybeans, to the foliarly
applied nitrOgen minerals, appeared to be related to
the fertilizer ingredient characteristics. At the low-
est rate, 10 pounds ammonium nitrate gave the highest
yield in contrast with checks and the other sources of
nitrogen fertilizer but at higher rates it reduced the
yield very sharply. The reduction in yield might be
due mainly to the verthigh salt index number and ion
effect of ammonium nitrate. As it is obvious from
Figures 9, 10 and 11 the ammonium nitrate burned the
leaves of soybeans more severely than did urea and
calcium nitrate, respectively, when applied at the 30
pound rate.

The rate and source of fertilizer nitrOgen applied
as foliar, to some extent, had some effect on the number
of pods per plant and the number of seeds per plant (Fig-
ures 12 and 13). For all three nitrogen sources, all
rates above 10 pounds reduced seed size (Figure 14). The
sources and the rates of nitrogen fertilizer did not

have a significant effect on the number of pods per plant,

42

 

Figure 9...Burning effect on soybean foliage caused
by ammonium nitrate at 30 lbs/A.

 

Figure 10...Burning effect on soybean foliage caused
by urea at 30 lbs/A.

. "of

43,

 

Figure 11...Burning effect on soybean foliage caused
by calcium nitrate at 30 lbs/A.

 

I
60 ./4‘ -—4
Ck ./ \ \
\

50 ‘ ‘\\\\\ .:::>///’.
4“ .\. \\
a X
'3 40
Q: ' O Ca(NO3) 2
.3 l NH4NO
o ' 3
a. ' Urea
‘& IIIIIIIiIIIyllIIIIIIIjIIIIII-II'IIIIIIIII'IIIIIII

10 20 30 4O

RATE OF NITROGEN (lbs/A)

Figure 12 .. Number of Pods per Soybean plan as Affected by the
Rate and Source of Nitrogen by Foliar Application.

45

140

 

130

1|“ 5 \

# seeds/Plant

110 '-.
\ O
/"
100 O /
\.
90
A
80
' - Ca(NO3)2
A NH4NO3
I a Urea
10 , 20 30 4o

RATE (lbs N/A)

Figure 13... Number of Seed per plant of soybeans as Affected by
the Rates and Sources of Nitrogen by Foliar Application.

46

 

 

17"
ck :\
n::\\\l\ ,-
\fi“"’\“\
15
§ ./ ..__w *‘as
33
o 14 O Ca(NO3)2
a ' A 111145103
2 ' . Urea
w
u
5‘ IIIIIIIIIIqIIIIIIIII'IIII-III-FII-IIIIII'IIIIIII
10 20 30 40

RATE (lbs N/A)

Figure 14... Seed size of soybean plants as affected by the rate
and source of Nitrogen by foliar application.

47

number of seeds per plant or seeds per pod at different
positions of the individual plants, such as the top,
middle and the bottom, since these plant characteristics

were already deve10ped at the time of foliar application.

CON CLUS IONS

Results from this experiment led to the conclusion
that the time and rate of nitrogen application can affect
the yield of soybeans. When fertilization of soybeans
with calcium nitrate was carried out within the first
five weeks of the growing season, 45 pounds of actual
nitrogen resulted in better yields than the 90 pound
rate. After five weeks after planting, it seemed that
the soybeans responded more positively to the 90 pound
rate rather than the 45 pound rate.

In summary, fertilizing soybeans with nitrogen
after nodules have formed on the roots seems to hold
some promise for increasing yields. However, decisive
conclusions cannot be reached regarding the physiologic
or economic returns from delayed application of nitrogen
to soybeans based on these studies due to uncontrolled
environmental fluctuations. Optimum growing conditions
for soybeans occurred only the first year of investigation.
Based on the lack of variability in the data of that
year the possibility of increased soybean yields by

allowing nodulation to occur and then adding nitrogen

48

49

as a side-dress or foliar spray seems very real. How-
every, additional data is needed before a definitive

statement can be made.

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BIBLIOGRAPHY

 

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52.

53.

54.

55.

56.

57.

58.

59.

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55

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57

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82.

58

(1974): Legume Inoculation and Seed

 

Treatment: (Technical Information for Farmers
and Applicators): Compiled and written by the
Research Staff of the Rudy - Patrick Company
Seed Treatment Laboratory: Princeton, Illinois
U.S.A.: Pp: 4.

APPENDIX

Table 8... Analysis of variance table for Soil Application

of Calcium Nitrate (dependent Variable is Yield)

—-

 

Source of Variance S.S. d.f. MS F
Year 1914.76 2 957.38 38.33**
Rep (year) 190.72 6 31.80 1.27
Rate 5.35 l 5.35 0.21
Year x Rate 135.04 2 67.52 2.70
Error 1 149.85 6 24.97

Time 257.64 9 28.63 1.77“
Year x Time 208.00 18 11.56 0.71
Rate x Time 337.86 9 37.54 2.31*
Year x Rate x Time 308.35 18 17.13 1.06
Error 2 1748.39 108 16.19

Total 5255.98 179

** Significance at 1% level

* Significance at 5% level

° Significance at 10% level

59

60

Figure 15... Number of seed per soybean plant as affected
by the time and rate of nitrogen application

in the soil for 1975 and 1976

o
3
2

220

210

 

ucuam\mouou *

45 lbs N/A

90 lbs N/A

10

TIME (weeks after planning)

62

50

 

/

46 .\. ./a
:: /\. \./

 

43" ‘
S t/
51 II ck
'O .
3’ ‘ /
N . ‘ ‘
A d. / \;/
t
39
I ./
33 O 1973
' O 1975
I 1976
I
0 3 4 5 6 7 8 9 10

TIME (weeks after planting)

Figure 16... Yield of Soybeans for 1973, 1975, and 1976 as Affected
by the Time of Nitrogen Application in the soil.
Averaged over both 95 and 90 pound rates

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