Residue-Management Practice Effects on Soybean Establishment and Growth in a Young Wheat-Soybean Double-Cropped System

Research was conducted on silt-loam Alfisols at the Pine Tree Branch (PTBS) and Cotton Branch (CBES) Experiment Stations. Prior to the initiation of this study, both study locations were cropped under CT; thus the results of this study represent a short-term NT history. Previous crops were sorghum (Sorghum bicolor L.) and soybean at PTBS and CBES, respectively. The research area was established at both locations in Spring 2002 and repeated in Spring 2003. In Fall 2001 and 2002, ‘Coker 9663’ wheat was drill-seeded with a 7.5-inch row spacing at both locations. In Spring 2002, 48 10-ft by 20-ft plots were established at both locations. In 2003, the exact same plots as in 2002 were used again. All plots were fertilized with a 90 lb/acre broadcast application of N as urea (46% N) in early March 2002 and 2003. To obtain different levels of wheat residue, one half of the plots were fertilized with an additional 90 lb N/acre broadcast application as urea during the late-jointing stage in late March 2002 and 2003. After wheat harvest in early June 2002 and 2003, the residue-burning treatment was imposed on half of the plots. Following burning each year, the CT treatment was imposed. Glyphosate-resistant soybean, ‘Pioneer 95B32’, maturity group 5.3, was drill-seeded with a 7-in row spacing at both locations each year. Soybeans were harvested in early November 2002 by hand due to wet soil conditions, but were harvested using a plot combine in late October 2003. Soybean yields from 2002 and 2003 were adjusted and reported on a 13% moisture basis. To capture potential effects of tillage, burning, and wheat-residue level throughout the growing season in addition to final yield, plant populations were measured early in the growing season (i.e., 8 to 10 and 30 days after planting) and at mid-season growth BACKGROUND INFORMATION AND RESEARCH PROBLEM