Soybean Maturity Group and Row Spacing Choices for Maximizing Light Interception in the US Midsouth.

Light interception is a key factor affecting soybean yields and crop competitiveness with weeds. A comprehensive analysis of planting date and maturity group (MG) combinations for common row spacing in the US Midsouth  may be useful for detecting scenarios that will ensure reaching full canopy and interception of sufficient cumulative photosynthetically active radiation (CIPAR) for obtaining high yields and for competing against weeds. A set of light interception functions as a function of thermal time were obtained from 2 years of experimental data from planting date and MG studies for a narrow (0.46-0.48 m) and a twin row spacing (0.19-0.20 m twin rows on 0.96 m beds) under a constant seeding density of 35 plants m^-2 under irrigated conditions. Prediction of soybean developmental stages was performed with DSSAT-CROPGRO-Soybean (v. 4.5.1.023) for different scenarios: MG choices 3 to 6, planting dates from early April to late June, and 30 years of weather data from Rohwer and Fayetteville, AR. The regressions obtained experimentally of LI with thermal time were used to investigate LI at R1 and R5 for each scenario and row spacing, the probability of intercepting sufficient CIPAR, and the time interval to reach full canopy.