Soybean Yield Optimization Using Nitrogen Applications.

Although soybean (Glycine max) yields have shown great increase since first being cultivated in the U.S., even greater increase is in demand.  Nontraditional practices being implemented into traditional cropping systems, such as applying nitrogen to soybean for yield optimization, might be one of many solutions to fill this demand for improvement. Various nitrogen rates were applied at planting, V2 and R2 stages in Irrigated full season and dryland double crop field studies to evaluate nitrogen effect on soy yield. Both dryland and irrigated environments had numerically greater biomass where nitrogen was applied, but statistical significance varied. When early season dry weights were analyzed, greater biomass was observed in some nitrogen treatments compared to the zero nitrogen treatment under dryland conditions, but no statistical differences were seen in an irrigated environment. Mid-season nodulation seemed to be lower when nitrogen was applied, but not significantly lower. Late season nodulation analysis indicated there was no effect on mid-season nodulation by fertilizer treatments within dryland and irrigated environments. Mid-season biomass data suggested there were no differences in plant growth in both environments. Thus, the fertilizer rates did not have an effect on biomass at the timing dates. Post-harvest seed weights did not suggest any differences in seed size among treatments in dryland and irrigated environments. Yield results showed that no significant differences among treatments within both environments were observed in the field. A mean separation analysis did show differences among treatments, but this was not supported by the F test. Consequently, nitrogen fertilizer application at planting, V2 or R2 stage appeared to have no effect on soybean yield for the two environments. Although, continued research is being conducted to conclude further results.