Late-Planted Soybean Yield Response To Row Spacing, Seeding Rate and Maturity Group Under Rainfed Conditions In The Southern Plains.

Although innumerous technologies and production strategies have contributed for greater soybean [Glycine max (L.) Merr.] yields throughout the country, unique production aspects still needs to be addressed in the Southern Plains. The most common period for soybean production in Oklahoma is late-season, resulting in low canopy formation and low yields due to short period left for the soybean crop to complete its life cycle. The effect of different management practices on late-planted soybean yields has not yet been evaluated in Oklahoma. The objective of this study is to evaluate the effects of maturity group (MG), row spacing, and seeding rate on late-planted soybean seed yield under rainfed conditions. Five locations were sowed in late June/early July from 2011 to 2013. Seeding rate ranged from 198,000 to 383,000 seeds ha^-1, row spacing were 19 cm, 38 cm, and 76 cm, and MG IV and V were selected. Yield analysis were performed and correlated to canopy closure measurements. In 2011 and 2012 site-yr, extensive periods with very high temperatures and no rainfall, lead to an overall poor soybean growth and yield . In 2011, no difference was observed among treatments except for 38 cm row spacing planted at 321,000 seeds ha^-1, which had the highest yield for both MGs. In 2012, treatments showed no yield differences using MG 4.8. For MG 5.6 greater yields were observed only at 38 cm row spacing when planted at the two highest seeding rates. MG 5.6 had in general greater yields than MG 4.8. For 2013, treatments at same seeding rate showed greater canopy closure at 19 and 38 cm compared to 76 cm row spacing. Seed yields for 2013 locations are still under evaluation; therefore conclusions were not established yet.