Glufosinate applied to glufosinate-resistant crops may drift and injure glufosinate-sensitive crops. A 2-yr field study examined glufosinate effects on plant injury, chlorophyll content, nodulation, nitrogenase activity, leaf nitrogen, yield, and seed composition in soybean. Glufosinate drift was simulated by application at 45？g/ha to glyphosate-resistant and conventional (glufosinate-sensitive) soybean at 3 weeks after planting (WAP). Glufosinate effects were also evaluated in glufosinate-resistant soybean at 450？g/ha applied twice at 3 and 6 WAP. In glufosinate-resistant soybean, chlorophyll, nitrogenase activity, root respiration, plant biomass, and yield were not affected; seed nitrogen and protein were increased; seed oil content decreased. In glufosinate-sensitive soybean, glufosinate caused 28-32% injury and decreased 35-42% chlorophyll content within 3？d after treatment (DAT) but soybean completely recovered by 14 DAT. Glufosinate had no effect on plant biomass, nitrogenase activity, and root respiration in 2009 and inconsistent effects in 2010. In glufosinate-sensitive soybean, glufosinate had no effect on yield; increased leaf nitrogen, seed protein, and oleic acid; decreased oil content, linoleic, and linolenic acid. Glufosinate-sensitive soybean exposed to glufosinate drift may exhibit transient injury but soybean could recover without a yield penalty. Glufosinate altered seed composition in all soybean types. 1. Introduction Glufosinate[2-amino-4-(hydroxymethylphosphinyl)butanoic acid] is a nonselective, postemergence herbicide that controls a broad spectrum of annual and perennial grass and broadleaf weeds in crop and noncrop lands [1–4]. Glufosinate transport in xylem or phloem is limited [1, 5, 6] thus thorough spray coverage is required for complete kill of targeted weeds. As glufosinate cannot move to underground rhizomes and stolons, the control of perennial weeds is limited. Glufosinate inhibits glutamine synthetase, the enzyme that converts glutamate and ammonia to glutamine [7]. Following glufosinate application, ammonia levels in plants increase dramatically, resulting in metabolic disruption and plant death. Glufosinate disrupts many important nitrogen metabolism (nitrogen assimilation) reactions in plants by inhibiting glutamine synthesis and indirectly inhibiting electron flow in photosynthesis. Ammonia reduces the pH gradient across the membrane which uncouples photophosphorylation [1, 7, 8]. Injury symptoms such as chlorosis and wilting usually occur within 3–5？d after glufosinate application, followed by necrosis in 1-2
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