CHLORIMURON ADSORPTION, DESORPTION, AND DEGRADATION IN SOILS FROM CONVENTIONAL TILLAGE AND NO-TILLAGE SYSTEMS

No-tillage (NT) and other conservation management practices designed to enhance plant residue accumulation can affect the herbicides fate in soil. This study was designed to evaluate adsorption, desorption, and degradation of chlorimuron {ethyl 2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl)amino]carbonyl]amino] sulfonyl]benzoic acid} in soils collected from long-term conventional tillage (CT) and NT plots. Soils were Miami silt loam (fine-silty, mixed, mesic, Typic Hapludalf) and Drummer silty clay loam (fine-silty, mixed, mesic, Typic Endoaquoll) from Illinois, and Dundee silt loam (fine-silty, mixed, thermic Aeric Ochraqualf) from Mississippi. Adsorption was determined on five concentrations of C-14-chlorimuron (0.22-12.26 mu mol kg(-1)) equilibrated for 72 h. Desorption in four cycles (1, 24, 24, and 24 hr) was measured for samples initially sorbed at 2.60 mu mol kg(-1). Adsorption K-f values ranged from 0.55 to 6.53 and were higher in NT compared with CT soils. The N values were less than unity in all soils. Desorption was hysteretic and the total amount desorbed in four desorptions ranged from 18 to 51% of that sorbed. Desorption K-f values ranged from 0.60 to 2.74 and were higher in NT compared with CT soils. After 63 d incubation of C-14-chlorimuron, 44 to 54% of applied remained as extractable chlorimuron and 10 to 16% of applied mineralized to (CO2)-C-14 among the soils. Half-Life of over 2 mo and relatively low mineralization suggests poor adaptability of native microbial populations to chlorimuron as substrate. Differences in the chlorimuron degradation pattern were minor between NT and CT soils, despite NT soils in general having greater organic C, microbial populations, and soil enzyme activity compared with CT soils.