Turfgrass thatch effects on pesticide leaching: a laboratory and modeling study

Process-based models are frequently used to assess the water quality impacts of turfgrass management emanating from proposed or existing golf courses. Thatch complicates the prediction of pesticide transport because surface-applied pesticides must pass through an organic-rich layer before entering the soil. This study was conducted to (i) compare the use of a linear equilibrium model (LEM) and two-site nonequilibrium (2SNE) model to predict pesticide transport through soil and thatch + soil columns, and (ii) evaluate thatch effects on pesticide transport through soil columns with a volume-averaging approach. Pesticide breakthrough curves were obtained for soil and thatch + soil columns from a 1 cm h(-1) flux applied one day after applying triclopyr (3,5,6-trichloro-2-pyridinyloxyacetic acid) and carbaryl (1-napthyl-methyl carbamate). Pesticide and bromide transport parameters indicated that nonequilibrium processes were affecting pesticide transport. Columns containing zoysiagrass (Zoysia japonica Steud.) thatch had lower triclopyr and carbaryl leaching losses than did soil-only columns, although total reductions attributable to thatch did not exceed 15% of the applied pesticide. When laboratory-based retardation factors were used, the 2SNE model explained 88 to 93% of the variability for triclopyr and 70 to 94% of the variability for carbaryl. Laboratory-based retardation factors performed well in a 2SNE model to predict the peak concentration and tailing behavior of triclopyr and carbaryl with a volume-averaging approach. These results suggest that separate representation of the thatch layer in process-based models is not a prerequisite to obtain reasonable estimates of pesticide transport under steady state flow conditions.