Updated May 5, 2021:
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Increasing Double Crop Soybean Yields through Intensive Management: Final Year
Katherine Rod, Carrie Knott, Carl Bradley, and Jordan Shockley

Introduction:
There has been recent interest from Kentucky soybean producers to increase double crop soybean
yields while remaining profitable. Double crop soybeans are grown in a more stressful environment
than full season soybeans, which includes a shorter growing period, higher temperatures, and lower
water availability during seed set and seed fill. The goal of this research was to identify
intensive management practices of the winter wheat double crop soybean rotational system to
increase soybean yield and profitability for Kentucky double crop producers.
Objectives:
The objectives of this study were to 1) determine the effect of wheat harvest timing on double crop
soybean yield, in the form of soybean planting timings; 2) investigate the effect of intensive
management programs on double crop soybean yield; and 3) evaluate the profitability of the
intensive management programs.
Materials and Methods:
This study was conducted in 2017, 2018, and 2019 on two different soil types at the University of
Kentucky Grain and Forage Center of Excellence in Princeton KY. Double crop soybean plots were
planted following wheat harvest at two different timings: early harvest at 20 to 22% grain moisture
and at the normal harvest timing of 13 to 15% grain moisture. The soybean trails were arranged in a
split plot randomized complete block design, where the main plot was planting timing, and the
split plot were the management treatments. Management treatments consisted of a combination of
seeding rate, the use of seed treatment, and foliar pesticide applications. Treatments were
replicated five times in each of the planting dates.
Treatments included:
1) 150,000 seeds/A planting population, no seed treatment, and foliar pesticide application when
economic thresholds were met – UK Rec
2) 150,000 seeds/A planting population, use of seed treatment, and foliar pesticide application
when economic thresholds were met – UK+ST
3) 150,000 seeds/A planting population, use of seed treatment, and a prophylactic foliar
pesticide application of Quadris Top and Warrior II with Zeon Technology at the R3 growth stage –
UK+ST+PF
4) 225,000 seeds/A planting population, no seed treatment, and foliar pesticide application when
economic thresholds were met – INT
5) 225,000 seeds/A planting population, use of seed treatment, and foliar pesticide application
when economic thresholds were met – INT+ST
6) 225,000 seeds/A planting population, use of seed treatment, and a prophylactic foliar
pesticide application of Quadris Top and Warrior II with Zeon Technology at the R3 growth stage –
INT+ST+PF


Early season plant populations were measured at approximately the V2 growth stage. Canopy closure
was measured once a week using the Canopeo software until the soybean canopy was fully closed.
Disease ratings (particularly frogeye leaf spot) and leaf defoliation ratings (to estimate insect
damage) were measured prior to the prophylactic pesticide application and at 14 and 21 days after
application for all soybean plots. Economic thresholds treatment plots were scouted once a week and
fungicide or/and insecticide was applied as needed. Harvest plant populations were measured at
physiological maturity prior to harvest. All soybean plots were harvested at approximately 13%
grain moisture and evaluated for yield. Yield component data of seed number m-², seed weight, pod
number and seeds per pod were measured. Grain samples from each plot were tested for protein and
oil content at the University of Minnesota NIR laboratory. Partial budget analysis was conducted to
evaluate the profitability of each of the intensive management treatments compared to the current
UK recommendation.
Results:
The three years of results indicate that there was an effect of the planting timing and management
treatments on soybean yield. Planting double crop soybean immediately after wheat harvested at 20
to 22% grain moisture had increased yields from approximately 10 to 12 bu per acre each year. In
2017, the early double crop soybean was planted 10 days before the normal planting timing while in
2018 and 2019 there was an approximate 21 day difference between the planting timings. Each of the
intensive management options: increased seeding rate, the use of seed treatments, and prophylactic
foliar pesticide application were examined, before looking at each of the six management
treatments. The increased seeding rate increased seed yield by approximately 5.5 bu per acre and
increased plant populations compared to the UK recommended seeding rate. There was no difference in
seed yield when the seed treatment was applied however, the plots with seed treatment had
significantly greater plant populations compared to the non-seed treated plots. The prophylactic R3
foliar pesticide application increased soybean yields by approximately 4 bu per acre in 2018 and
2019.
The six intensive management treatments were then evaluated for yield (Figure 1). The most
intensive management treatment (INT+ST+PF) had the greatest yield, however it was similar to the
INT+ST treatment. The four treatments of UK+ST, UK+ST+PF, INT, and INT+ST had similar yields to
each other. The UK Rec treatment had the lowest yield, however it was still similar to the UK+ST,
UK+ST+PF, and INT treatments.
Economic evaluation of each of the intensive management treatments compared to the UK
recommendation is important to determine the profitability of each management treatment. Partial
budget analysis was conducted to determine the double crop soybean management profitability. The
partial budget analysis (Table 1) indicates that two treatments had positive net benefits compared
to the UK recommendation while three treatments had negative net benefits. The INT+ST+PF, the high
intensive management treatment, had a positive net benefit of almost $5 per acre while the INT
treatment of the higher seeding rate, had a positive net benefit of almost $12 per acre. These two
positive net benefits show that there is a possibility of some intensive management practices being
profitable.
Results from this project are currently apart of K. Rod’s PhD dissertation, and will be published
in a peer review journal, which was submitted in summer of 2020. It is still under review, but we
are hopeful it will be published late-winter 2021. Based upon these findings, and additional
research, University of Kentucky’s recommendations for double crop soybean production were revised.


Figure 1. Yield of the six intensive management treatments from two locations at Princeton KY in
2018 and 2019. Treatments included: UK-Rec: 150,000 seeds/A, no seed treatment, foliar pesticide
applications at economic thresholds; UK+ST: 150,000 seeds/A, seed treatment, foliar pesticide
applications at economic thresholds; UK+ST+PF: 150,000 seeds/A, seed treatment, prophylactic R3
pesticide application; INT: 225,000 seeds/A, no seed treatment, foliar pesticide applications at
economic thresholds; INT+ST: 225,000 seeds/A, seed treatment, foliar pesticide applications at
economic thresholds; and INT+ST+PF: 225,000 seeds/A, seed treatment, prophylactic R3 pesticide
application.
Yields are adjusted to 13% grain moisture. Means labeled with the same letter are not
significantly different (P 0.05).

Table 1. Partial budget analysis of the intensive management treatments to determine profitability.
Each treatment is compared to the UK Rec treatment which is the UK’s current double crop soybean
recommendation. Treatments include: UK-Rec: 150,000 seeds/A, no seed treatment, foliar pesticide
applications at economic thresholds; UK+ST: 150,000 seeds/A, seed treatment, foliar pesticide
applications at economic thresholds; UK+ST+PF: 150,000 seeds/A, seed treatment, prophylactic R3
pesticide application; INT: 225,000 seeds/A, no seed treatment, foliar pesticide applications at
economic thresholds; INT+ST: 225,000 seeds/A, seed treatment, foliar pesticide applications at
economic thresholds; and INT+ST+PF: 225,000 seeds/A, seed treatment, prophylactic R3 pesticide
application. The average October 2019 Kentucky soybean price of $8.89 was used (USDA, NASS, 2020).













Intensive Management Treatments


UK Rec



UK+ST



UK+ST+PF



INT



INT+ST



IN+ST+PF















Inputs


150,000 seeds a-¹/ No Seed treatment/ Foliar Pesticide Application at economic thresholds
150,000 seeds a-¹/ Pioneer Premium Seed Treatment/ Foliar Pesticide Application at economic
thresholds
150,000 seeds a-¹/Pioneer Premium Seed Treatment/Prophylactic R3 Pesticide Application 225,000
seeds a-¹/No Seed Treatment/ Foliar Pesticide Application at economic thresholds
225,00 seeds a-¹/Pioneer Premium Seed Treatment/As Needed Foliar Pesticide Application
225,000 seeds a-¹/Pioneer Premium Seed Treatment/Prophylactic R3 Pesticide Application















Yield

bu/a 50.5

51.2



53.9



55.5



56.0



61.0














Additional Cost



$0.00



$18.21



$46.58



$32.68



$60.00



$88.37














Additional Benefit
per acre

$0.00



$6.22



$30.23



$44.45



$48.90



$93.35














Net Benefit



$0.00



-$11.99



-$16.35



$11.77



-$11.10



$4.98