Considerable concern exists about pesticide losses and contamination of ground water with intensely managed turfgrass systems. Triazine herbicides such as simazine are subject to high mobility in the sandy soils commonly found beneath golf course fairways in coastal regions of the southeastern U.S. In these experiments, we investigate the influence of organic matter binding on degradation of ¹⁴C-simazine [6-chloro-N,N'-diethyl-1,3,5-triazine-2,4-diamine] in soils from turfgrass systems of widely varying ages that have differing levels of organic matter. Simazine additions to sterile soil revealed substantial potential for binding to organic matter. Binding capacity was related to organic matter content, with 58, 83 and 78% of applied ¹⁴C bound in soils from 5, 21 and 95 yr old turfgrass systems after 16 weeks of incubation. When non-sterile soil with high biological activity was examined, significant organic matter binding still was present. Release of ¹⁴CO₂, presumably resulting from biological degradation and cleavage of the triazine ring, was the primary fate of simazine, as 73, 77 and 54% was released from the three types of soils. Bound simazine still accounted for 17, 19, and 31% of applied ¹⁴C even after 16 weeks of incubation. Furthermore, ¹⁴C binding was evident to a greater soil depth with the older turfgrass systems. These results indicate that organic matter and simazine interactions are an important determinant of simazine leaching potential. As turfgrass systems age and organic matter levels increase, the potential for simazine leaching into groundwater decreases even though biological degradation rates may be lower.