Soybean Development is Affected by Method and Timing of Rye Control in Cover Crop Systems

Cover crops provide many environmental and soil quality benefits, yet their adoption into production agriculture has been limited by insufficient management information. This study was conducted to determine a combination of method and timing of rye (Secale cerealeL.) control that would not hinder soybean [Glycine max(L.) Merr.] growth or result in resource competition. The effects of mechanical and chemical rye control at 2nd node, boot, and anthesis growth stages on soil water, light interception, soybean growth and maturity were investigated near Boone, IA, on Spillville loam (Fine-loamy, mixed, superactive, mesic Cumulic Hapludolls), and Clarion loam (Fine-loamy, mixed, superactive, mesic Typic Hapludolls) in 2002 and 2003 growing seasons. In 2002, untimely rainfall reduced soil water 0.0325 kg kg-1from 2nd node to anthesis in the 0–15 cm depth in chemical control. In mechanical control, rye depleted soil water until it matured, at which point larger plants in check subplots utilized soil water at a higher rate than soybean in treatments with rye. Soybean light interception was reduced by rye in mechanical treatments in both years. Anthesis and check plots in chemical control had similar values for light interception. Biomass accumulation was lower under mechanical control than chemical control. However, even the best treatment in chemical control, anthesis, accumulated 140 g m–2less biomass than check treatments in 2002. All treatments containing rye delayed maturity. Anthesis timing matured closest to check subplots at 6.5 and 3.8 days after the check in 2002 and 2003, respectively. The possibility of allelopathy delaying maturity is worthy of further investigation. Chemical control at anthesis was the most effective management system next to the check, differing significantly only in date of maturity. Periods of low rainfall, ineffective rye control, and possible allelopathy were critical limiting factors in this rye cover crop system.