Seeding rate effects on soybean maturity group IV-VIII for the southeastern production system: I. vegetation indices

Abstract

Increasing seeding rates in wide row spacing soybean [Glycine max (L.) Merr.] may improve vegetation growth. This study evaluated vegetation indices of five maturity groups (MGs) at six seeding rates (68,000; 136,000; 204,000; 272,000; 340,000; and 408,000 seeds ha-1) under dryland conditions for soybean production system on the southeastern coastal plain in 2007-2009. In this region, MG IV is part of early soybean production system (April planted), MG V and VI are full-season soybean (May planted), and MG VII and VIII for double-cropping system (June planted). Leaf area index (LAI) varied with seeding rate by linear functions at 60 and 90 days after planting (DAP) for MG IV in 2008/2009, V in 2007/2008, and VIII in 2008; by quadratic functions at 60 and 90 DAP for MG V and VI in 2009, 60 DAP for MG VII in 2007, and 90 DAP for MG IV in 2007 and VII in 2008. Normalized difference vegetation index (NDVI) increased with seeding rate linearly at 60 DAP for MG IV, V, VI, and VIII in 2008, IV and V in 2009; at 90 DAP for MG IV in 2008, VI and VII in 2009. Quadratic responses of NDVI to seeding rate were found at 60 DAP for MG VI in 2009 and VII in 2008; 90 DAP for MG IV and V in 2009, VII and VIII in 2008. Results suggest that increasing seeding rate may improve soybean growth at early development stages; however, increase of seeding rate above 272,000 seeds ha-1 may not achieve significant improvement of vegetation growth. © 2011 by the American Society of Agronomy.