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Title: EFFECT OF SOIL CONDITIONS ON THE DEGRADATION OF CLORANSULAM-METHYL

Author
item CUPPLES, ALISON - UNIV OF ILLINOIS
item Sims, Gerald
item HART, STEVEN - UNIV OF ILLINOIS

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Cloransulam-methyl is a new herbicide recently registered for broadleaf weed control in soybean. The herbicide was applied to approximately 1% of soybean fields in the US for the first time in 1998. General environmental properties have been published by the manufacturer, however data are lacking on the impact of environmental conditions on fate of the compound in soil. Studies were performed to determine the effects of soil moisture and temperature on degradation and sorption of cloransulam-methyl in soil. Results of the investigations showed that the rate of loss of the herbicide from soil increases with increasing temperature, although the individual processes contributing to disappearance exhibit varied responses. Microbial degradation of cloransulam-methyl appears to be optimal at 25 degrees C whereas incorporation of the compound into soil organic matter mimicked disappearance of the compound. Most fate processes were unaffected by soil moisture over the range employed in this study (20-60% of pore space filled with water), although complete decomposition of the compound to carbon dioxide was stimulated by increasing soil moisture. The results of these investigations will be used to understand the environmental behavior of cloransulam-methyl and other herbicides in soil, and will be useful in optimizing the herbicidal properties of the compound as well. The impact of applying the results obtained will be to facilitate the development of decision aids that reduce offsite transport of pesticides and minimize the occurrence of carryover damage to crops in rotations.

Technical Abstract: Herbicide efficacy and environmental fate are often controlled by soil conditions. Aerobic soil laboratory studies were undertaken to determine the degradation of the herbicide cloransulammethyl [N-(2-carbomethoxy-6- chloro-phenyl)-ethoxy-7-fluoro[1,2,4]triazolo [1.5-c]pyrimidine-2- sulfonamide] for a range of soil factors. Treatments included soil temperature (5, 15, 25, 40, and 50 degrees C), moisture (20, 40 and 60% water filled pore space) and soil type (Drummer silty clay loam and Cisne silt loam). Variability in molecular degradation was investigated using two radiolabeled forms [Pheny-UL-14C] and [Pyrimidine-7,9-14C]). Dissipation of parent in soil solution and sorbed phases, formation of radiolabeled metabolites, 14C-mineralization, total microbial respiration and bound residue formation were measured for up to 120 days. Dissipation of parent and formation of bound residues in Drummer soil increased with greater temperatures. The influence temperature on 14C-mineralization, however, was dependent on position of radiolabel, suggesting that distinct groups of microorganisms degrade different parts of the molecule at higher temperatures. Only 14C-mineralization was influenced by moisture, with the response depending on soil type. Increasing moisture in Drummer soil resulted in more 14C-mineralization, which was attributed to increased microbial access to pesticide. In Cisne soil, which contained less clay and organic carbon, there was no effect at the highest moisture levels. Reduced availability may explain the increased persistence of parent in Drummer, compared to Cisne soil. Such increased dissipation in Cisne soil may have been responsible for the greater occurrence of bound residues in this soil.