Influence of Seeding Rate On Weed Pressure and Plant Growth of Different Maturity Groups Soybeans.

Plant reductions may contribute to increase in weed pressure. The objective was to evaluate the influence of seeding rates on weed pressure and plant growth of maturity groups (MG) IV through VIII soybeans [Glycine max (L.) Merr.] grown in the Southeastern U.S. under dryland conditions in 2007 and 2008. Soybeans were planted at approximately 55,000, 82,500, 110,000, 137,500, and 165,000 seeds acre^-1. Variety DP 4331RR (MG IV) was planted on 12 April, DP 5915RR (MG V) and AG 6301 (MG VI) on 9 May, Pioneer 97M50 (MG VII) on 4 June, and AGS 825 (MG VIII) on 18 June 2007. In 2008, variety AG 4801 (MG IV) was planted on 22 April, DP 5631 (MG V) and AG 6451 (MG VI) on 7 May, and V74N4RR (MG VII) and Prichard RR (MG VIII) on 3 June. Plant growth was evaluated based on the plant leaf area index in 2007 and 2008, and normalized difference vegetation index (NDVI) in 2008. Overall, weed pressure increased with decreased soybean seeding rates and was negatively correlated with soybean yields. Plant leaf area index generally increased with increased seeding rate and was positively correlated with soybean yields. However, plant NDVI varied across maturity groups and seeding rates.