The Impact of Soil Characteristics and Land Use on Sorption of Ionic and Non-Ionic Herbicides.

Sorption is a key factor determining herbicide environmental fate and behavior. Sorption of the same compound differs in various environmental and soil conditions. The overall goal of this research is to systematically compare the effect of soil physicochemical characteristics and land use on sorption of ionic (atrazine) and non-ionic (metolachlor) herbicides. Atrazine is chosen for it is one of the most widely used herbicides in the world and in the U.S., and its use has been controversial. Metolachlor is selected because it is widely used in diverse agronomic crops, and it is among one of the most commonly detected herbicides of groundwater contamination. Sorption isotherms were conducted for soils from three land uses including cropland, turf, and woods of two depths, with various soil characteristics. Initial data for atrazine show that the sorption is greatest on soils collected in woods whereas it is least on soils collected from croplands. Soils from depths of 0-5 cm had higher atrazine sorption than from depths of 5-15 cm in woods and turf, but not in cropland. Among soil organic carbon (SOC), soil pH, texture, and humic matter content, SOC concentration alone predicts sorption fairly well (r² = 0.92) in a stepwise sorption prediction model. The research for metolachlor is ongoing currently, and will be concluded by July, 2016. Collectively, this research is yielding new insights for predicting how soil conditions and land use influence herbicide predict sorption, leaching, and runoff, thereby providing broad utility for improved herbicide management.