Soil organic matter changes in turfgrass systems aff ect binding and biodegradation of simazine

Abstract

Concern about pesticide losses from maintained turfgrass areas led us to examine the fate of the triazine herbicide simazine in turfgrass systems and, specifi cally, interactions between simazine binding to soil organic matter and biodegradation. Soil samples were removed from turfgrass systems of different ages, placed in microcosms, conditioned as sterile or nonsterile, and exposed to 14C-simazine. At seven sampling intervals, the soil was extracted and 14C was separated into three pools; bound, extractable, and CO 2. With sterilized surface soil (0-5 cm), 52, 70, and 71% of applied 14C-simazine was bound to soil from the 4-, 21-, and 99-yr-old turfgrass systems, respectively, after 16 wk. With nonsterile conditions, biodegradation became dominant, as 60 to 80% of the 14C was recovered in the CO2 fraction and binding was held at ~20%. Among all soils evaluated, bound 14C and 14CO2 production was lower in subsurface soil (5-15 cm) from the 4-and 21-yr-old turfgrass systems. 14C-simazine disappearance time (DT50) values under nonsterile conditions ranged from 0.9 to 5.8 wk. Results indicate that turfgrass systems have a relatively low amount of simazine available for leaching as the systems age due to a large capacity for biodegradation and binding to organic matter.©Crop Science Society of America.