Early Planting Effect on Soybean Seed Protein and Oil.

Early planting of soybean to achieve high yields is becoming more common, but early planting may mean that the environment during which R5 through R6 growth stages occur may impact seed protein and oil concentrations. Our objective was to evaluate the effect of early planting on soybean seed composition. Three cultivars were sown at six planting dates (late March through early June) in West Lafayette, Indiana in 2006 and 2007. Protein and oil were determined using near-infrared reflectance spectroscopy. Early planting increased oil concentration and decreased protein concentration. Mean oil concentration decreased approximately 12 g kg^-1 as planting was delayed in both years. In 2006 average seed protein concentration varied by planting date, but ranged from 355 to 363 g kg^-1. In 2007 mean protein concentration increased 14 g kg^-1 as planting was delayed. Seed composition was associated with mean daily maximum temperature during R6. Delaying planting until late May or early June altered seed composition slightly.