Amitrole degradation in vineyard soils in relation to pedo-climatic conditions

The fate of [C-14]-amitrole herbicide was studied in eight soils having dif ferent capacities for amitrole mineralisation. Laboratory incubations were run combining different experimental conditions: temperature (4. 28 and 50 degreesC), soil moisture (50, 100 and 150% of soil water holding capacity) and microbial activity (sterile and non-sterile conditions). During incubat ion, samples: of the soils were periodically extracted with 0.5 M NH,OH and extracts were analysed by HPLC. The lengths of time needed for 50% dissipa tion of amitrole (DT50) in soils ranged from less than 1 day to more than 7 0 days. Amitrole mineralisation occurred only in nun-sterile soils, showing that it is a biological process. Mineralisation was lower in soils with a coarse texture than in soils with a fine texture. Soil water content had li ttle influence on the total amount of amitrole mineralised at the end of in cubation. Temperature had a greater influence on mineralisation. although r ates were still high at low and high temperatures. In non-sterile as in ste rile soils, the major product detected in the extracts was amitrole. Additi onal non-identified radioactivity was occasionally extracted. However, it n ever represented more than 10% of initially applied amitrole. Non-extractab le residues represented less than 15% of applied radioactivity in acidic so ils and about 30% of applied radioactivity in alkaline and neutral soils. T he amount of nonextractable radioactivity formed was enhanced in sterile as compared to non-sterile soils. Furthermore, in sterile soils, high tempera ture induced an increase of non-extractable residues, showing that amitrole is chemically quite reactive.