Bly A., H.J. Woodard, D. Winther
Introduction
Soybean grain production has increased from improved plant genetics. Production increases from management practices haven’t been as great. Yield response to narrow row spacing has been shown to be positive. Response to fertilizer application is rare and most notable with phosphorus when soil test P levels are low. Soybean plants receive N from symbiotic bacterium nodulation. Additions of N to soybean is not a standard practice. Some individuals believe N additions are necessary for maximum soybean production. A research project was initiated to evaluated the effect of N and Agrotain application at mid-pod fill growth stage (R3.5) on soybean yield parameters.
Materials and Methods
A research site was chosen near Brookings SD with no soybean cropping history in the past 5 years. Prior to planting, composite soil samples were taken from 0-6" and 6-24" soil layers for soil test analysis. One soybean variety from each maturity group 0, I, and II was no-till seeded into corn residue at 220,000 seeds/a in 7 inch rows on May 27, 1998. Seeds were treated with Bradyrhizobium japonicum inoculum. Plot size measured 5 by 62.5 feet. Immediately after planting 2.5 pts/a Broadstrike/Dual was broadcast applied for residual grass and partial broadleaf control. Select at 10 oz/a for volunteer corn and Lorsban at 16 oz/a for grasshopper control was applied on July 9, 1998. Lorsban at 16 oz/a for grasshopper control was also applied to this site on July 16 and 28, 1998. Fertilizer treatments consisted of a check without N and Agrotain, 50 lbs N/a as urea without Agrotain, and 50 lbs N/a as urea with impregnated Agrotain at 5 qts/ton fertilizer. Treatments were randomized within variety main blocks and replicated four times. N treatments were broadcast applied on the soil at mid-pod fill growth stage (R3.5). Plots were harvested with a plot combine on Sept. 25, 1998. Grain weight and moisture was determine at harvest. Grain test weight was measured with mechanical methods and protein and oil content was determined with NIR spectroscopy. Comparison of dependent variable treatment means was completed with SAS.
Results and Discussion
Soil test N results showed 51.9 lbs NO3-N/a (0-2’). Soil P and K were considered in the "very high" category. Soil pH was 7.8 and organic matter was 3.2%. ANOVA analysis showed that variety significantly influenced only grain test weight and protein (Table 1). Fertilizer treatment significantly influenced only grain protein and oil. The variety and fertilizer treatment interaction did not significantly influence any dependent variable. The IA 2021 variety had the highest grain test weight and lowest grain protein (Table 2). The Parker variety had the highest grain protein. A trend for higher grain protein and a lower grain oil was associated with N application. However; protein and oil yield was not significantly different from the check treatment. Grain yield was not significantly influenced by variety or fertilizer treatment.
Conclusions
Application of N and Agrotain at soybean mid-pod fill growth stage (R3.5) did not significantly influence grain, protein, and oil yield.
Acknowledgment
This project was partially funded by the South Dakota Soybean Research and Promotion Council and the SD Ag. Experiment Station.