Pesticide sorption by soil is among the most sensitive input parameter in many pesticide leaching models. Organic matter is the most important soil constituent influencing pesticide sorption by soils. Bermudagrass is a perennial crop with a constant deposition of organic material creating a soil system that can change drastically with time. Therefore, sorption characteristics of the herbicide simazine [6-chloro-N,N'-diethyl-1,3,5-triazine-2,4-diamine] on five soils and three soil macroorganic matter density fractions were studied. Surface soils (0-5 cm) from bermudagrass systems of five different ages were air-dried and passed through a 4-mm sieve. Macroorganic matter from two soils were further separated into three separate density fractions using colloidal silica solutions with differing specific gravities. Using a batch-equilibrium method, adsorption isotherms were determined for each soil and macroorganic matter fraction. Sorption was greatest on the oldest soil system and decreased with age of the bermudgrass soil system. Sorption and soil system age was directly related to organic matter levels in the soil. These results indicate leaching potential and bioavailability of simazine may decrease as bermudagrass systems age.