SOIL METABOLISM OF THE HERBICIDE RIMSULFURON UNDER LABORATORY AND FIELD CONDITIONS

Procedures were developed for soil analysis of rimsulfuron and its met abolites by means of GC-ECD, GC-FPD and GC-MS with a detection limit o f 1 mu g of rimsulfuron equivalents per kilogram of dry soil, after pu rification of the soil extracts by TLC. Soil containing an exaggerated rimsulfuron concentration was incubated in the laboratory, in order t o adjust the analytical procedures. To evaluate the role of different manuring managements, rimsulfuron was applied postemergence (10 g ha(- 1) on a corn field in 1994 and 1995) on plots treated with (1) green m anure, pig slurry applied in (2) November and (3) March, and cow manur e applied in (4) November and (5) March and (6) untreated control plot s without organic fertilizer. Neither rimsulfuron nor its metabolites were detected at soil depths lower than 8 cm. The results show that ma nure managements prolong rimsulfuron half-life in the 0-8 cm surface s oil layer from a minimum of 14 days (control) to a maximum of 46 days (pig slurry in March). At corn harvest, rimsulfuron and its metabolite s were not detected in soil. Similar soil degradation pathways were ob served in the field as in the laboratory. imidin-2-yl)-N-[3-(ethylsulf onyl)-2-pyridinyl]urea 2 was a transient soil degradation product. ony l)-2-pyridinyl]-4,6-dimethoxy-2-pyrimidineamine 3 attained a maximum s oil concentration after 20 days of incubation and then progressively d isappeared and could not be detected after 40 days. The high-molecular weight amine 3 did not accumulate in soil, eliminating the concern fo r potential formation of nitroso amino compounds. 2-Hydroxy-3-(ethylsu lfonyl)pyridine 4 became the major rimsulfuron soil degradation produc t. The soil concentrations increased and attained a maximum after 40 d ays of incubation and then decreased; its isomerization into 2-pyridon e, followed by hydrolysis, could transform it into low molecular weigh t nontoxic products. The concentrations of 2-amino-4,6-dimethoxypyrimi dine 5 were somewhat lower than those of compound 4.