Metribuzin Degradation Kinetics in Organically Amended Soil

The rates of degradation of metribuzin [4-amino-6- tert -butyl-3-(methylthio)- as -triazin-5(4 H )-one] were determined in an untreated Portneuf silt loam, in soil with added organic amendments, and in soil previously treated with metribuzin. While first-order rate kinetics generally described the degradation of the metribuzin in the soil, a quadratic expression was superior. Organic amendments were found to inhibit or accelerate the rate of breakdown of metribuzin depending upon the kind of amendment. Neither a lag phase nor an enrichment was observed from prior treatment with metribuzin.