Metribuzin degradation in soil: II—effects of tillage

A 140‐day laboratory incubation, using surface soil from a long‐term soybean tillage study, evaluated tillage influence on [ 14 C]metribuzin degradation. Higher plant residue conditions in no‐tillage (NT) soil inhibited metribuzin mineralization to [ 14 C]carbon dioxide as compared to metribuzin degradation patterns observed in conventional tillage (CT) soil. At 140 days, relative abundance of extractable 14 C components in NT included polar metabolites > metribuzin = deaminated metribuzin (DA) = deaminated diketometribuzin (DADK), while in CT, components included metribuzin > polar metabolites > DADK≫DA. Conditions in NT apparently inhibited polar 14 C degradation, and resulted in its accumulation, while in CT polar 14 C degradation proceeded relatively rapidly. For both NT and CT, more 14 C was measured in an unextractable fraction than in any other fraction. A greater portion of the unextractable fraction in NT was associated with decomposed plant residue than in CT. Surface accumulation of crop residue, such as occurs under NT, provided a soil environment which altered metribuzin degradation patterns.