The Influence of Crop Inputs On US Soybean Yields.

Perceived stagnant yields and high commodity prices have led U.S. soybean farmers to consider additional crop inputs as potential management devices to increase soybean productivity.  In some cases, these inputs are being applied as “yield enhancing” products with little or no scientific evidence to support these claims.  This study was conducted to analyze the potential yield benefits and synergistic interactions crop inputs may have on soybean yields.  The study was initiated in 2009 as a six state (MN, IA, MI, KY, AR, and LA) collaborative project.  Each cooperating state used its respective university recommended best management production practices and adapted varieties for that region.  The yield response of additional soil fertility, seed treatment, seed applied inoculant, foliar fertilizer, and foliar fungicide in conjunction with wide (≥76 cm) and narrow row spacing (≤ 50.8 cm) was measured across all six states.  Products were applied at recommended label rates and growth stage.  A recommended seeding density of 345,800 seeds ha^-1 was used in 12 of the 14 treatments; two treatments received an additional 247,000 seeds ha^-1 and were considered ultra-high input systems.  A knock-out treatment structure was implemented to measure crop response to the selected crop inputs, including a control.  The treatment receiving all five inputs was termed the “kitchen sink” (KS) treatment.  All six states identified a significant yield increase in the KS treatment when compared to the control.  Further investigation revealed the observed response in the KS treatment was likely due, at least in part, to the application of foliar fungicide.  Disease ratings indicated the presence of foliar pathogens, though below economic threshold levels.  The removal of any of the other four inputs had little to no impact on soybean yield when compared to the KS treatment across states.  Data from 2009 and 2010 will be presented.