Laboratory degradation studies of bentazone, dichlorprop, MCPA, and propiconazole in Norwegian soils

Laboratory degradation studies were performed in Norwegian soils using two commercial formulations (Tilt and Triagran-P) containing either propiconazo le alone or a combination of bentazone, dichlorprop, and MCPA. These soils included a fine sandy loam from Hole and a loam from Kroer, both of which a re representative of Norwegian agricultural soils. The third soil was a hig hly decomposed organic material from the Froland forest. A fourth soil from the Skuterud watershed was used only for propiconazole degradation. After 84 d, less than 0.1% of the initial MCPA concentration remained in all thre e selected soils. For dichlorprop, the same results were found for the fine sandy loam and the organic-rich soil, but in the loam, 26% of the initial concentration remained. After 84 d, less than 0.1% of the initial concentra tion of bentazone remained in the organic-rich soil, but in the loam and th e fine sandy loam 52 and 69% remained, respectively. Propiconazole was show n to be different from the other pesticides by its persistence. Amounts of initial concentration remaining varied from 40, 70, and 82% in the referenc e soils after 84 d for the organic-rich soil; fine sandy loam, and loam, re spectively. The organic-rich soil showed the highest capacity to decompose all four pesticides. The results from the agricultural soils and the Skuter ud watershed showed that the persistence of psopiconazole was high. Pestici de degradation was approximated to first-order kinetics. slow rates of degr adation, where more than 50% of the pesticide remained in the soil after th e 84 d duration of the experiment, did not fit well with first-order kineti cs.