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MISSISSIPPI SOYBEAN PROMOTION BOARD
PROJECT NO. 56-2014 (YEAR 2)
2014 Final Report
Title: Impact of Irrigation Initiation Timing on Plant Development and Yield of Indeterminate
and Determinate Soybean Varieties
Principal Investigator: Trent Irby ([email protected])
BACKGROUND AND OBJECTIVES
Irrigation capability is an extremely important factor in Mississippi soybean production. As the
Mississippi alluvial aquifer is an important natural resource and increased demand of this
resource threatens the sustainability of its use, it is imperative to explore non-yield limiting
options which can contribute to conservation of both the aquifer and the environment in general.
A widely utilized practice of soybean irrigation initiation in Mississippi is applying water at first
bloom (R1). In some cases, it is possible that soil moisture deficits are not reached when
irrigation is initiated at R1. If this is the case, it could be possible to delay irrigation initiation
until deficit in soil moisture is reached without jeopardizing yield potential.
As research projects are currently in place to address this issue, it is important to gather
information about how varieties with different growth habits respond to irrigation initiation at
different growth stages. In other words, indeterminate and determinate varieties may not respond
similarly to irrigation initiated at different reproductive growth stages. In addition, evaluation of
plant development (i.e. pod placement and number of seed within each pod), seed quality, and
yield may provide useful insights in determining response of indeterminate and determinate
varieties.
With advancements in technology which allow rapid development of new varieties, it is
important to understand how advanced, popular varieties planted in today’s production systems
will respond to a range of different irrigation timings.
Objective 1: Provide an economical assessment of irrigation costs associated with various
irrigation initiation timings.
Objective 2: Evaluate potential differences in plant development and yield following
different irrigation initiation timings.
Additional experiments associated with an M.S. student project:
Evaluation of irrigated and non-irrigated systems on soybean with differing growth habits
under differing plant populations.
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REPORT OF PROGRESS/ACTIVITY
In both 2013 and 2014, the irrigation initiation studies faced great difficulty. Both years saw
extremely wet conditions during the optimum planting window. Rain continued to be a major
factor throughout both growing seasons.
In 2013 the DREC location remained under water after planting and the plots did not reach an
adequate stand. The Brooksville location in 2013 reached a stand, but rains throughout the
reproductive growth stages prohibited the targeted moisture deficits from being achieved. Similar
struggles were observed in 2014 and also did not allow for either location, DREC or Sidon, MS,
to achieve the correct deficits during the early reproductive phases. Because this project is
associated with an M.S. student, additional projects were in place during both years where
supplemental data were collected to partially address this objective. For clarity, objective two
data will be presented first, followed by objective one’s economic assessment of the data of
objective two.
Objective 2: Evaluate potential differences in plant development and yield following
different irrigation initiation timings.
Four irrigation initiation timings were selected to reflect critical areas of plant development as
well as a non-irrigated (NI) treatment. These initiation timings included the producer standard
(PS—initiating irrigation at first bloom or R1), delaying irrigation initiation until pod
development (R4), and delaying irrigation until beginning seed development (R5). The other
delayed initiation treatment was based off of the FAO56 model, which is triggering irrigation
when deficit levels reached a 2 in. soil moisture deficit. In both years, this 2 in. deficit first
occurred during the late R2 (full bloom) growth stage. Once a treatment was initiated, irrigation
was maintained to keep soil moisture deficits under 2 in. according to FAO56 for any given
treatment until maturity (R7) was reached.
Tracking soil moisture deficits using the FAO56 model showed that during both years the
soybean crop was over the “threshold” of 2 in. soil moisture deficit for the non-irrigated and
delayed irrigation treatments (R4 and R5 initiation) during the R2 to R4 growth stages. In 2013
that deficit continued to deepen through the R5-initiated treatment. By delaying irrigation past
the producer standard, water was saved and pumping costs were lowered because of the reduced
number of irrigation applications (Table 1.1). With the reduction in water applied, no significant
difference occurred in yield with this reduction in irrigation applications by delaying all the way
through R5. In 2012, a significant yield advantage was measured when irrigation was delayed to
R5 compared to the producer standard of initiation at R1. An average of 20 bu/ac yield
advantage was seen for all irrigated treatments when compared to the NI treatment (Table 1.2).
Plant development was also measured through number of seed within each pod, total number of
pods, and pod and bean weight for a m2 of row for each initiation treatment. In 2012, seed weight
for all irrigated treatments was significantly greater than seed weight from the NI treatment.
Total pods and pod weight had no significant difference in 2012. In 2013, total pod and pod
weight for all irrigated treatments were greater than for the NI treatment, with the R4-initiated
treatment having the greatest total number of pods (Table 1.3). The number of seed in each pod
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(i.e. pod type) was not different among irrigation treatments in 2012. In 2013, the R5-initiated
treatment had the greatest number of one- and two-bean pods (Table1.4). This smaller pod
number did not translate to a yield reduction or lower pod/bean weight.
Objective 1: Provide an economical assessment of irrigation costs associated with various
irrigation initiation timings.
An economic analysis of the irrigation initiation experiment to measure gross and net returns for
both years was conducted with the assistance of Dr. Larry Falconer, Extension Economist with
MSU. Irrigation was initiated at 4 different stages. A NI treatment was included for comparison
purposes. The economic analysis took into account cost of irrigation applications, holding all
other costs constant. This reflects the savings, in dollars, by delaying irrigation initiation with no
adverse effect on yield/return.
In some cases, a slight yield increase was seen by delaying irrigation applications (Table 1.2). In
2012, net returns for all delayed initiation treatments were higher than the producer standard.
Statistically, the R5-initiated treatment had a significantly higher return than the producer
standard treatment. In 2013, irrigated treatments were not significantly different for gross or net
return. Although not significantly different, the R4-initiated treatment resulted in the highest net
return.
Additional experiments associated with the M.S. student project:
Objective: Evaluate soybean yield of differing growth habits planted under various seeding
rates in irrigated and non-irrigated systems.
Experiments were conducted in 2013 and 2014 in both Starkville, MS at the R.R. Foil Plant
Science Research Center (North Farm) and in Stoneville, MS at the Delta Research and
Extension Center (DREC) to evaluate 6 different soybean seeding rates under irrigated and nonirrigated systems for indeterminate and determinate soybean varieties. Plots were set up in a
randomized complete block design with a split-plot arrangement of treatments. The main factor
was irrigation system and the sub-factor was seeding rate within maturity group. Seeding rates
used were 90,000, 105,000, 120,000, 135,000, 150,000, and 165,000 seeds per acre. Once a full
crop stand had been established, stand counts were recorded from each treatment. At crop
maturity, final plant height and yield were recorded.
The DREC location received three irrigations in both 2013 and 2014 for the irrigated plots, while
both years of Starkville’s plots received two irrigations. Stand counts indicated that 90% or
greater of the intended seeding rate was achieved. Furthermore, plant height data indicated that
as seeding rate increased, plant height increased. Yield data are still being analyzed. Preliminary
analysis indicates that yield varied by location, but in general the higher seeding rates (135k to
165) resulted in greater yields. Regression analysis will be run on these data to find a possible
peak in return from seeding rate.
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IMPACTS AND BENEFITS TO MISSISSIPPI SOYBEAN PRODUCERS
With the implications that irrigation applications could be saved without reducing yield, all
Mississippi soybean producers with irrigation capability could see direct benefit from this
research both now and in the future. Presently, these data support MSU-ES and MSPB
recommendations for irrigation efficiency by scheduling irrigation events using sensors or some
type of applied scheduling tool rather than just initiating irrigation at first flower regardless of
soil moisture. In doing so, producers have the ability to increase returns and reduce costs while
maintaining or boosting yield. Along with lowering costs and increasing net returns, reducing
irrigations could contribute to conserving the Mississippi Alluvial Aquifer.
END PRODUCTS - COMPLETED OR FORTHCOMING
Data collected from this study will be used in an M.S. thesis and will be edited for publication in
2015. Along with an M.S. thesis, this initiation study will be submitted for review to be
published in a journal in 2015.
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Table 1.1. Irrigation initiation dates, number of applications made, acre-inches applied, and
effective rainfall plus irrigation in acre-inches.
Irrigation
Initiation
Number of
AcreAcre-Inches +
Year Initiation Timing
Date
Irrigation Events Inches
Rainfall
2012
NI
------------11.85
PS
May 17, 2012
6
24
35.85
FAO
May 24, 2012
5
20
31.85
R4
June 4, 2012
4
16
27.85
R5
June 22, 2012
4
16
27.85
2013
NI
------------3.67
PS
May 31, 2013
8
21
24.67
FAO
June 17, 2013
6
17
20.67
R4
June 25, 2013
5
16
19.67
R5
July 8, 2013
4
16
19.67
Table 1.2. Yield and economic returns for each irrigation initiation timing treatment as
affected by yeara.
Irrigation
Year Initiation Timing
Yieldbc
Gross Returnbd
Net Returnbef
2012
NI
63.98 c
971 c
971 c
PS
82.41 b
1251 b
1105 b
FAO
84.03 ab
1275 ab
1143 ab
R4
83.27 ab
1264 ab
1145 ab
R5
85.95 a
1304 a
1184 a
2013
NI
47.06 b
647 b
634
PS
70.68 a
971 a
811
FAO
68.69 a
944 a
803
R4
70.17 a
964 a
832
R5
66.46 a
913 a
792
a
Data were split between years due to year being highly significant for yield and returns when
compared across years.
b
Means within a column for each respective crop followed by the same letter are not
significantly different based on Fisher’s protected LSD at p≤0.05.
c
Yield expressed as bu/ac.
d
Yield per bu/ac x market price.
e
Gross income less irrigation costs (all other costs assumed fixed).
f
Net Return in 2013 not significantly different among initiation timings.
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Table 1.3. Total pods and pod and bean weight in a m2 for each irrigation initiation timing
treatment as affected by environmenta.
Irrigation
Plantsc
Year Initiation Timing
per m2
Total Podsde
Pod Weightde
Bean Weightd
2012
NI
25
1179
643
394 b
PS
23
1293
840
543 a
FAO
24
1322
839
542 a
R4
23
1376
849
558 a
R5
25
1371
837
513 a
2013
NI
18
545 c
194 c
108 c
PS
21
759 b
279 b
151 bc
FAO
19
895 ab
343 ab
176 ab
R4
20
955 a
358 a
178 ab
R5
22
903 ab
386 a
217 a
a
Data were split between years due to year being highly significant for pod count and weight
when compared across years.
b
Means within a column for each respective crop followed by the same letter are not
significantly different based on Fisher’s protected LSD at p≤0.05.
c
No significant difference for plants m2 for either 2012 or 2013.
d
Data collected from plants in a m2
e
No significant difference among initiation treatments in 2012.
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Table 1.4. Pod development (pod type) in a m2 of row for each irrigation initiation timing
treatment as affected by environmenta.
Irrigation
Blank
One-Bean Two-Bean Three-Bean Four-Bean
Year Initiation Timing
Podsc
Podsd
Podsd
Podsc
Podsce
2012
NI
13
62
346
714
44
PS
12
61
295
865
59
FAO
34
87
311
832
56
R4
14
59
328
923
52
R5
11
60
357
895
48
2013
NI
49
192 c
197 c
108
--PS
51
264 b
309 b
135
--FAO
53
307 b
365 ab
171
--R4
42
305 b
377 ab
179
--R5
50
375 a
407 a
123
--a
Data were split between years due to year being highly significant for pod count and weight
when compared across years.
b
Means within a column for each respective crop followed by the same letter are not
significantly different based on Fisher’s protected LSD at p≤0.05.
c
No significant difference among initiation timings in either 2012 or 2013.
d
No significant difference among initiation treatments in 2012.
e
No four-bean pods were found in 2013.
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