Systematic Optimization of Yield-Enhancing Applications: Population Interactions.

Many U.S. soybean growers have adopted an input-based management approach using purported yield enhancing products and prophylactic applications of pesticides in place of a traditional active management system. Many of these inputs and practices are being used while little authentication of their effectiveness has occurred. Furthermore, interactions between plant population and an input-based management system have not been validated.  A cooperative multi-state field study was initiated during 2012 and 2013 at two locations each in Wisconsin, Michigan, Illinois, Indiana, Kentucky, Iowa, and Arkansas; three locations in Kansas; and four locations in Minnesota. The objective of this study was to determine how grain yield and seed quality respond to a more intensive management system at varying plant populations. Two management regimes were evaluated (untreated and a high input system termed, SOYA complete) at six targeted seeding rates ranging from 123,500 to 494,000 seeds ha^-1. The SOYA complete management regime consisted of multiple agricultural products currently being marketed to soybean growers (seed-applied fungicide, insecticide, biologicals, LCO promoters, and foliar-applied fertilizer, insecticide, and fungicide) which were applied at label rates and timings. Stand counts were taken at V2 and R8 growth stages to confirm planting and harvest plant populations. Growing season conditions during 2012 and 2013 were highly variable due to weather extremes. Maximum grain yields were dependent on growing region; however, a higher seeding rate was generally required to maximize grain yields in the southern U.S. vs. the central and northern U.S. Although the use of the SOYA complete management system did increase yields, no interaction between plant population and management system has been revealed. Field research will continue through the 2014 growing season. The large number of site-years will allow for the development of detailed production recommendations related to inputs and seeding rates throughout major soybean growing areas of the U.S.