Maximizing Agronomic Input Efficiency for Soybean Growth and Yield in a Double-Crop Wheat-Soybean System Produced in Virginia, USA.

Field experiments were conducted in 2012 in a wheat-soybean double-crop system at three Virginia locations to evaluate seeding rate, seed-applied inoculant, starter N applied at planting, cultivar growth habit, and foliar fungicide application on soybean vegetative response and seed yield. Experiments were conducted as a split-plot in a randomized complete block design replicated four times. Factors tested included main plot foliar fungicide (untreated or disease free management), and sub-plot, which was a factorial arrangement of soybean cultivar growth habit (indeterminate or determinate), seeding rate (592,800 or 716,300 seed ha^-1), seed-applied liquid inoculant (untreated or with Bradyrhizobia japonicum), and application of UAN solution at planting (untreated or 30 kg N ha^-1). Data collection focused on V4 and R8 plant height, V4 and R5 whole plant tissue N, R4 canopy reflectance, yield component analysis, seed yield, 100 seed weight, and oil and protein concentration. Location main effect influenced seed yield, therefore results are presented separately by location. When UAN was applied at planting at Painter location, cultivars’ seed yield did not differ, however when UAN was not applied, 95Y01 out-yielded 95Y20 by 331 kg ha^-1. At Suffolk, when UAN application was applied, cultivars’ seed yield did not differ, however, without UAN application, 95Y20 increased seed yield by 11% compared to 95Y01. Foliar fungicide applied at Suffolk increased seed yield by 6% compared to untreated. When foliar fungicide was not applied at Painter, decreased seed yield was observed for both cultivars compared to no fungicide application.