Environmental Factors and Soil Amendment Affect the Decomposition Rate of Dazomet Fumigant

Dazomet (3,5-dimethyl-1,3,5-thiadiazinane-2-thione) is widely used as a soil fumigant for controlling soil-borne diseases and pests in China and other agricultural countries. The active ingredient of dazomet is its degradation product, methyl isothiocyanate. Little is known about the environmental conditions that affect the degradation of dazomet in soil. In this study, we conducted laboratory incubation experiments to test the effects of several environmental factors, including soil texture, water content, temperature, pH, and soil amendments, such as chicken manure or urea fertilizer, on the decomposition of dazomet. Results showed that dazomet degradation in soil is an abiotic process strongly dependent on soil texture, water content, temperature, and pH. Decomposition rates differed greatly in various soils, depending mainly on soil physicochemical properties such as pH and organic matter content. The degradation rate increased by 15 to 24 times and by 16 to 37 times when soil temperature increased from 5 to 45°C, and water content increased from 10 to 30%, respectively. Dazomet degraded faster in alkaline versus acidic soil. Both chicken manure and urea fertilizer moderately slowed dazomet degradation. Dazomet was degraded in soil mainly by hydrolysis. The results of our study contribute to a better understanding of the environmental behavior of dazomet, potentially leading to its more efficient, safe, profitable, and effective use by farmers.