PERSISTENCE OF METRIBUZIN AND METABOLITES IN 2 SUB-ARCTIC SOILS

Persistence and leaching of C-14-metribuzin -dimethyl)-3-(methylthio)- 1,2,4-triazin-5(4H)-one] and metabolites were determined in Tanana (lo amy, mixed, nonacid Pergelic Cryaquept) and Beales (sandy, mixed Typic Cryochrept) silt loam soils under irrigated potato (Solanum tuberosum L.) and dryland barley (Hordeum vulgare L.) conditions in the subarct ic. Overall, dissipation of total C-14 (metribuzin and metabolites) wa s significantly slower (P > 0.05) in Tanana than Beales soil over the first 105 d, but by 468 d, the C-14 remaining (51% of applied) did not differ (0.05 < P) between soils. Initial degradation of metribuzin wa s rapid in both soils but was not significantly different between soil s (0.05 < P). At 35 d after application 24% of applied metribuzin rema ined, At the end of the study (468 d), 5.0% of the applied metribuzin was still present. Unextractable residues accounted for the greatest a mount of C-14 remaining in the soils. of the extractable metabolites, greater amounts of desaminometribuzin were found in both soils than di ketometribuzin or desaminodiketometribuzin. More water moved through t he irrigated than nonirrigated soil as evidenced by bromide movement. Also, more C-14 moved to 15 to 22.5 cm depth in the irrigated than in the nonirrigated soil, but < 1% of applied C-14 was detected below 22. 5 cm for both soils and irrigation treatments. Rapid metribuzin degrad ation in combination with sorption processes minimized leaching of tot al metribuzin residues through these subarctic surface soils.