LEACHING AND TRANSFORMATION OF GLUFOSINATE-AMMONIUM AND ITS MAIN METABOLITE IN A LAYERED SOIL COLUMN

Results from a long‐term study on leaching and transformation of the herbicide glufosinate‐ammonium (ammonium‐DL‐homoanalin‐4‐yl (methyl)phosphinate) in a layered soil column were compared with model calculations. Soil columns with layers of loamy sand and sand were treated with 3 kg/ha glufosinate‐ammonium, applied to the soil surface. The soils were irrigated and the leachate was monitored for glufosinate‐ammonium and the main metabolite 3‐methylphosphinico‐propionic acid during a period of 256 d. Calculations for glufosinate‐ammonium and the metabolite were performed with the soil column model EXSOL. Linear equilibrium sorption coefficients (Kd) and first‐order half‐lives were used for fitting effluent curves for both the herbicide and the metabolite. Sorption coefficients were compared with those values estimated from a relation to the clay content derived from batch studies. Fitted half‐lives were compared with the results from die‐away and 14CO2 evolution studies of both the parent and the daughter compound. The observed leaching of glufosinate‐ammonium could be well simulated using Kd (0.5 cm3/g) and half‐life (11.2 d). The half‐life fitted for the metabolite (10–30 d) was a factor 2 to 3 smaller than that measured with batch degradation experiments. This may be the result of using degradation data estimated by 14CO2 evolution, which only indirectly indicates the disappearance of the compound. Copyright © 1990 SETAC