The transgenic Liberty Link® (LL) soybean is tolerant to glufosinate, conferred by the enzyme phosphinothricin acetyltransferase (PAT), which is encoded by the pat gene from Streptomyces viridochromogenes. Because symptoms of injury can be observed in soybean [Glycine max (L.) Merr.] plants in some situations, this study evaluated the effects of rates of glufosinate on agronomic performance; quality of LL soybean seeds; and the ammonia, glufosinate, and N-acetyl-l-glufosinate concentration (NAG) in soybeans with and without the pat gene after application of increasing glufosinate rates. Field and greenhouse experiments were conducted; the first evaluated the selectivity of glufosinate in LL soybeans, and the second evaluated the metabolic changes in soybeans with (LL) and without (RR2) the pat gene, after application of glufosinate. For fieldwork, application of glufosinate at rates up to four times the maximum recommended caused initial injury symptoms (up to 38.5%) in LL soybean plants. However, no negative effect was found on seed quality and agronomic performance of LL plants, including yield. This shows the selectivity of glufosinate promoted by pat gene insertion for application in POST (V4), in LL soybean. For the greenhouse experiment, it was concluded that the LL soybean plants presented high glufosinate metabolism, lower ammonia concentration, and no reduction in dry matter, in comparison with RR2 soybean, after application of high rates of glufosinate.

Field experiments were conducted in 1998 and 1999 at two locations in Mississippi to determine weed control efficacy of postemergence soybean herbicides alone or following pendimethalin + imazaquin preemergence in glufosinate-tolerant soybean planted in 38- or 76-cm rows. Glufosinate applications controlled pitted morningglory better than conventional herbicide treatments, regardless of row spacing. Pendimethalin + imazaquin did not increase the efficacy of glufosinate on pitted morningglory. Pitted morningglory control was increased in narrow rows when compared to wide rows with all treatments. Sicklepod control ranged from 90 to 100% in narrow rows with glufosinate, regardless of rate. Residual herbicides alone controlled sicklepod 54%, regardless of row spacing. With grass species, two applications of 420 g ai/ha glufosinate controlled weeds 82 to 100%. Residual herbicides followed by 420 g/ha glufosinate controlled grass species 80% or more, regardless of row spacing. Hemp sesbania control ranged from 80 to 92% in 76- and 38-cm rows with one application of 560 g/ha glufosinate. Glufosinate at 420 g/ha used as sequential applications controlled hemp sesbania better than the conventional treatment in 76-cm rows. Residual herbicides in combination with glufosinate did not increase hemp sesbania control. There were no differences in yield due to row spacing at Stoneville in either year due to extremely dry growing conditions during pod set. At Starkville, two applications of 420 g/ha glufosinate resulted in higher yields than pendimethalin + imazaquin followed by 420 g/ha glufosinate in both years. Pendimethalin + imazaquin followed by 420 g/ha glufosinate increased yield in narrow rows compared to wide rows at Starkville in 1998.