FLUOMETURON BEHAVIOR IN LONG-TERM TILLAGE PLOTS

Fluometuron (N, N-dimethyl-N'-[3-(trifluoromethyl) phenyl] urea) is a preemergence herbicide used widely for weed control in cotton (Gossypi um hirsutum L.). Field research results suggest that many herbicides, including fluometuron, may be subject to preferential transport and le aching through the soil profile. The objectives of this study were to evaluate the distribution and leaching of fluometuron in a Lexington s ilt loam (Typic Paleudalf) through 3 years of study by analyzing depth incremented soil samples and tension-free pan lysimeter leachates col lected at a soil depth of 90 cm under no-till (NT) and conventional ti llage (CT, disc 2x - roller harrowed) management. Fluometuron depth di stribution following application and subsequent rainfall was related t o soil organic carbon content, with tillage effects restricted to the surface 2-cm. The amount of herbicide remaining in the soil profile af ter application decreased with increasing rainfall amounts. On average , 11% of applied herbicide in NT and 6% in CT remained in the surface 15 cm after 1 year. Fluometuron was detected in all lysimeter leachate s during the 3-year period. Peak herbicide leachate concentrations ran ged from 68 mg L(-1) to 1700 mg L(-1), depending on herbicide applicat ion in relation to rainfall timing. Annual leaching losses ranged from 5 to 53% of applied fluometuron during the study. Of the amounts lost to leaching, 68 to 100% (averaging 87% of the total lost to leaching) were lost during the first two or three significant rainfall events a fter treatment. Rainfall timing in relation to herbicide application w as the dominant effect in herbicide mobilization through the soil prof ile. Antecedent soil moisture content (predicted from rainfall amounts prior to fluometuron application) also influenced the appearance of l eachate and herbicide in the lysimeters, with lower soil moisture cond itions at application producing lower preferential flow. Depth-increme nted soil sampling after initial rainfall events was a poor mechanism for detecting fluometuron mobility through the soil profile. The rapid ity at which fluometuron was detected in the lysimeter leachates, the exceedingly high fluometuron concentrations, and the variability in le achate collection by the lysimeters, illustrated the significance of p referential flow The influence of tillage practice on the volume of dr ainage collected by the lysimeters and on fluometuron leaching was of little significance when compared with the influence of natural infilt ration heterogeneity.