Persistence of Metribuzin and Metabolites in Two Subarctic Soils

Abstract

AbstractPersistence and leaching of 14C‐metribuzin [4‐amino‐6‐(1,1‐dimethyl)‐3‐(methylthio)‐1,2,4‐triazin‐5(4H)‐one] and metabolites were determined in Tanana (loamy, 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 subarctic. Overall, dissipation of total 14C (metribuzin and metabolites) was significantly slower (P > 0.05) in Tanana than Beales soil over the first 105 d, but by 468 d, the 14C remaining (51% of applied) did not differ (0.05 < P) between soils. Initial degradation of metribuzin was rapid in both soils but was not significantly different between soils (0.05 < P). At 35 after application 24% of applied metribuzin remained. At the end of the study (468 d), 5.0% of the applied metribuzin was still present. Unextractable residues accounted for the greatest amount of 14C remaining in the soils. Of the extractable metabolites, greater amounts of desaminometribuzin were found in both soils than diketometribuzin or desaminodiketometribuzin. More water moved through the irrigated than nonirrigated soil as evidenced by bromide movement. Also, more 14C moved to 15 to 22.5 cm depth in the irrigated than in the nonirrigated soil, but <1% of applied 14C was detected below 22.5 cm for both soils and irrigation treatments. Rapid metribuzin degradation in combination with sorption processes minimized leaching of total metribuzin residues through these subarctic surface soils.