SULFENTRAZONE SORPTION, DESORPTION, AND MINERALIZATION IN SOILS FROM 2 TILLAGE SYSTEMS

Sulfentrazone sorption kinetics, desorption, and mineralization were e valuated in surface 7.5 cm of soils collected from long-term conventio nal-till (CT) and no-till (NT) plots. The soils used were Miami silt l oam and Drummer silty clay loam from Illinois and Dundee silt loam fro m Mississippi. Sulfentrazone sorption kinetics in Dundee silt loam CT and NT soils were adequately described by a simple two-site equilibriu m/kinetic model. Rapid initial sorption (within 1 h) was followed by a slower sorption and equilibrium, largely achieved by 72 h of shaking, with a negligible increase in sorption thereafter. The sorption K-f r anged from 1.02 to 3.44 among the six CT and NT soils. The K-f values were greater for NT compared to their respective CT soils. Overall, K- f values were higher in Drummer silty clay loam followed by Dundee sil t loam and Miami silt loam soil. The N values were less than unity in all soils indicating nonlinear sorption. Sulfentrazone desorption was hysteretic with a very low rate of desorption. The total amount desorb ed in four desorptions ranged from 58 to 72% of that sorbed. Less than 2.1% of applied C-14-sulfentrazone was mineralized to (CO2)-C-14 in D undee silt loam CT and NT soils during a 77-d incubation. Relatively l ow mineralization ion of sulfentrazone suggests poor adaptability of n ative microbial populations that have not been exposed to this herbici de. Higher sorption and lower desorption of sulfentrazone in NT soils compared to CT soils suggest that NT systems (which tend to increase p lant residues) may prolong sulfentrazone residence time in soil.