Fluometuron wash-off from cover crop residues and fate in a loessial soil

Cover crop residues on no-till soil will intercept a portion of applied her bicides. Thus, herbicide efficacy in no-till systems depends, in part, on r ainfall to wash the herbicide onto the soil. Tillage and cover crop residue may also influence sorption and degradation of a herbicide in soil. This s eries of studies examined fluometuron [N,N-dimethyl-N '-[3-(trifluoromethyl )phenyl]urea] wash-off from native vegetation, hairy vetch (Vicia villosa), and wheat residue (Triticum aestivum), related wash-off to sorption on the se residues, and compared fluometuron sorption and degradation in soil from long-term native, vetch, and wheat cover crop plots used with either conve ntional or no-till cotton (Gossypium hirsutum). A rainfall simulator was us ed to wash spray-applied fluometuron from plant material. Through-flow was analyzed for fluometuron by high-performance liquid chromatography. More fl uometuron was washed off native vegetation than vetch or wheat residues, wh ich retained fluometuron about equally. Fluometuron sorption on these resid ues was determined in a batch study. Sorption was least with native vegetat ion (K-D = 11 L kg(-1)), and there was minimal difference between vetch and wheat in sorption (K-D = 17 L kg(-1)). Fluometuron wash-off could be model ed from the batch sorption data. Sorption of fluometuron in surface soil fr om each tillage by cover crop combination was determined in a batch experim ent. Sorption was adequately described by the Freundlich model with N simil ar to 0.9 for all soils but K values of no-till soils (average similar to 2 L kg(-1)) nearly twice that of corresponding conventional-till soils. Degr adation of fluometuron in these surface soils was determined by incubating fortified samples for 6, 15, 30, and 60 days. Soil extracts showed that deg radation was more rapid in any no-till soil than in its conventional-till a nalog. Within either tillage treatment, degradation was slowest in vetch so il. Half-lives ranged from 7 and 8 days (no-till native and wheat soils, re spectively) to 51 days (conventional-till vetch soil). Fluometuron half-liv es in conventional-till wheat and native (19 and 27 days, respectively) and no-till vetch (31 days) soils were intermediate. Microbial activity was hi gher in no-till soil, consistent with faster degradation.