Influence of Seeding Rate on Weed Density in Soybean Planting System for Southeastern Coastal Plains

Problem statement: Increasing seeding rates may help decrease weed pressure in soybean [Glycine max (L.) Merr.] wide row spacing. Approach: The objective of this study was to evaluate the influence of five glyphosate-resistant soybean Maturity Groups (MG) (IV, V, VI, VII and VIII) and six seeding rates (68,000,136,000, 204,000, 272,000, 340,000 and 408,000 seeds ha^-1) on weed density under dryland conditions on the Southeastern coastal plain in 2007-2009. Results: Weed decrease with increasing seeding rate varied over years. Weed density was generally lower at higher seeding rates for most MG soybeans at 30 and 60 DAP, except MG IV and VIII at 30 DAP in 2007 and MG VI at 30 DAP in 2008. At 60 DAP, soybean leaf area index (LAI) and normalized difference vegetation index (NDVI) were greater with lower weed density. Conclusion: Additionally, negative correlations were observed between weed density and plant LAI/NDVI for all MG in 2008 and MG IV through VI in 2009. These results suggest that increased seeding rates may help decrease weed pressure and improve soybean growth at early growth stages. However the response of weed pressure to seeding rate may vary over years and depend on MG soybean.