Analysis of high yielding, early-planted soybean in Indiana
A trend toward early planting of soybean [Glycine max (L.) Merr.] in Indiana results in higher yield, but the limit to which a positive response to early planting occurs has not been evaluated. Our objective was to determine how early planting affects yield components and seed composition of indeterminate soybean planted in late March through early June in Indiana. Three cultivars (Pioneer brand 92M61, Becks brand 321NRR, and Becks brand 367NRR) were sown at six planting dates (late March through early June) in West Lafayette, IN, in 2006 and 2007. Across cultivars, yield in 2006 ranged between 4.24 to 4.43 Mg ha–1 at the planting dates from late March to mid-May, and decreased to 3.36 and 3.56 Mg ha–1 at later planting dates. In 2007, yield ranged from 4.21 to 4.44 Mg ha–1 for the 10 April, 30 April, and 9 May planting dates. Yield was reduced at the late March and early June plantings and ranged from 3.85 to 3.99 Mg ha–1. Path analysis revealed that pods m–2 had the greatest impact on yield, but seed mass was also an important constituent. 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. In 2007, mean protein concentration increased 14 g kg–1 as planting was delayed. Delaying planting until late May or early June altered seed composition slightly, but significantly reduced yield. Planting in April or early May is an effective management strategy to increase soybean yield in Indiana.