Tuesday, November 6, 2007
231-37
Effects of Organic Amendment on Degradation of 1,3-Dichloropropene and Chloropicrin in Soil.
Ruijun Qin1, Suduan Gao1, Dong Wang1, Husein Ajwa2, and Thomas Trout3. (1) USDA-ARS, Water Management Research Unit, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, CA 93648, (2) Department of Plant Sciences, University of California-Davis, 1636 East Alisal Street, Salinas, CA 93905, (3) USDA-ARS, Water Management Research, 2150 Centre Ave, Ft. Collins, CO 80526-8119
Soil fumigants, 1,3-dichloropropene (1,3-D) and chloropicrin (CP), are promising alternatives to the phased-out methyl bromide. However, these fumigants are volatile organic compounds and contribute to air pollution from emissions. Organic amendment to soils has been found effective to reduce emissions by increasing their adsorption or degradation but conditions to maximize this effect has not been well defined. This research investigated important factors affecting the degradation of fumigants under the amendment of organic materials. Laboratory incubation experiments were conducted for 15 days and the degradation rate of 1,3-D and CP in a sandy loam soil were determined under amendments with various organic materials, different temperature, and soil water content that increased from air-dry gradually to field capacity. Degradation of 1,3-D and CP showed a pseudo first-order kinetics. The degradation of 1,3-D isomers (cis-1,3-D and trans-1,3-D) was similar while the degradation of CP was generally faster than 1,3-D. Temperature increase accelerated fumigant degradation significantly, particularly for 1,3-D. Sterilization by autoclave did not reduce fumigant degradations indicating that chemical reactions between organics and fumigants were the primary mechanisms. The degradation of 1,3-D increased slightly when soil moisture increased while the degradation of CP was not affected. Amendment with steer manure, chicken manure, organic composts, and grape pomace enhanced fumigant degradation rate 2-3 times for 1,3-D compared to non-amended soil. The effects of organic amendments on CP degradation was more effective than on 1,3-D. Fumigant degradation rates increased as the amount of steer manure increased and there was no interaction between soil moisture and the manure. The results suggest that soil moisture, temperature and organic materials are important factors on the degradation of 1,3-D and CP and must be considered simultaneously to achieve low fumigant emissions in the field.