Rate of Degradation of Metribuzin and Two Analogs in Soil

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Abstract
The rates of degradation of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], the isopropyl analog [4-ammo-6-isopropyl-3-(methylthio)-as-triazin-5(4H)-one], and the cyclohexyl analog [4-amino-6-cyclohexyl-3-(methylthio)-as-triazin-5(4H)-one] in soil were determined under laboratory and field conditions. First-order kinetics best described the rate of degradation of the three herbicides. At 5 and 20°C, metribuzin and the isopropyl analog degraded more slowly than the cyclohexyl analog. At 35°C, the rates of degradation for all three herbicides were similar. The calculated half lives were approximately 329, 44, and 16 days for the three herbicides at 5, 20, and 35°C, respectively. Rates of 1.12 and 2.24 kg/ha, applied in the field, remained in the upper 5 cm of the soil profile, and the pattern of herbicide degradation followed that found in the laboratory study at 20°C.