Glyphosate-resistant soybean cultivar response to glyphosate

Glyphosate (N-(phosphonomethyl) glycine)-resistant (GR) soybean [Glycine ma r (L.) Merr.] technology is gaining acceptance in U.S. cropping systems, ye t potential yield suppression from either cultivar genetic differentials, t he GR gene/gene insertion process, or glyphosate is a concern. Other work s hows that the GR gene/gene insertion process may suppress soybean yield. No one has reported the effects of glyphosate on a diverse group of commercia lly available GR soybean cultivars. In this study we evaluated one oft he p otential sources of GR yield suppression-the effect of glyphosate on yield, growth, and development of GR cultivars. Field experiments were conduct ed at four Nebraska locations with 12 GR cultivars in 1998 and 13 GR cultivar s in 1999. Soybean response to glyphosate, ammonium sulfate (AMS), and mate r application at 21 and 42 d after soybean emergence was compared with cont rol plots treated with AMS and water in 1998. An additional control, water alone, was added in 1999. Grain yield among cultivars differed as expected with a range of 3.44 to 3.96 Mg ha(-1) in the 2-yr averages. Glyphosate did not affect the majority of the soybean growth and development characterist ics measured. Grain yield of GR soybean was not affected by glyphosate at a ny Location or when averaged over locations. Two-year average grain yield o f cultivars treated with glyphosate, AMS, and water was 3.74 Mg ha(-1); thi s was not different from 3.79 Mg ha(-1) with AMS and water treatment.