Evaluation of Seeding Rates On Maturity Group IV through VIII Soybeans.

The objective of the study was to evaluate the influence of reduced seeding rates on maturity groups (MG) IV through VIII soybeans [Glycine max (L.) Merr.] grown in the Southeastern U.S. under dryland conditions. The research project was conducted at Clemson University, Edisto Research and Education Center near Blackville, SC in 2007 and 2008. Maturity group IV through VIII soybeans in the plant population study were planted at 141,464, 212,197, 282,928, 353,662, and 424,392 seeds ha^-1. In 2007, soybeans DP4331RR (MG 4) were planted on 12 April, DP5915RR (MG 5) and AG6301 (MG 6) on 9 May, Pioneer 97M50 (MG 7) on 4 June, and AGS 825 (MG 8) on 18 June. In 2008, soybeans were planted on 22 April (MG IV - AG 4801), 7 May (MG V - DP 5631 and MG VI - AG 6451), and 3 June (MG VII - V74N4RR and MG VIII - Prichard RR). Soybean yields were not influenced by seeding rates for any MG in 2007. In 2008, there was no difference between seeding rates for MG IV through VI. However, significantly lower yields were obtained from the lowest seeding rate of 141,464 seeds ha^-1 for MG VII, and lower yields for MG VIII soybeans at 141,464 and 212,197 seeds ha^-1. Generally, averaged across years and all MG soybeans, the results showed that seeding rates can be reduced to about 212,197 seeds ha^-1 without significant yield reductions. Moreover, grain yields were negatively correlated with weed pressure and positively correlated with leaf area index, plant height, and grain moisture.