ABSTRACT
This chapter considers two ammo acid biosynthesis inhibitors — glyphosate and glufosinate (phosphinothricin; bialaphos). The applications of glyphosate in agronomy are wide ranging, essentially limited only by its lack of selectivity. Glyphosate degradation has been generally attributed to microbial activity, as demonstrated by its persistence in experiments involving sterilized or sodium azide-treated soils. Glufosinate and bialaphos have found wide use as postemergence herbicides in agriculture and horticulture despite their essential nonselectivity, particularly in noncropping and minimum-tillage situations, and as preharvest desiccants. A number of explanations for the wide variation in in vitro microbial resistance — or at least tolerance — toward glyphosate may be advanced. Conflicting evidence of the effect of glyphosate on soil respiration rates has accumulated. The ability of the soil microflora to degrade cellulose is of particular importance in minimum- or no-tillage cultivation, in which glyphosate is frequently used for sward clearance prior to direct drilling.
