Adsorption and Degradation of Metolachlor in Alluvial Soils: Effect of Poultry Litter

Abstract

Soils in the Southern Mississippi Valley Alluvium (MLRA 131) have low organic matter content (< 20 g kg-1) and application of poultry (Gallus gallus domesticus) litter to these soils may improve their quality. However, after litter application, chemical weed control practice such as herbicide application for row crop production remains the same. In soils where soybean [Glycine max (L.) Merr.] is grown, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl] acetamide] is applied as a pre-emergent herbicide to control broadleaf and annual grasses. There is an opportunity for metolachlor to leach to the groundwater during and after rainfall events. We hypothesize that metolachlor applied to these alluvial soils amended with poultry litter may degrade rapidly when compared to unamended (control) soils. Soil samples were collected from the top 10 cm of Commerce silt loam (Aeric Fluvaquents) and Sharkey clay (Vertic Haplaquepts). The samples were air dried and amended with poultry litter to increase the organic matter content to 20 g kg-1. Control samples received no poultry litter but were subjected to similar protocols as the amended samples. Batch experiments indicated significant increase in metolachlor adsorption for the amended soils, although adsorption was higher in Sharkey clay. Kinetics experiments showed that equilibrium was established 2 h for Commerce silt loam and 24 h for Sharkey clay. Metolachlor degradation was 6 times faster in the amended Commerce soil and 2.5 times faster in the amended Sharkey soil. Degradation rate in the amended Commerce soil was 2.3 times faster than the amended Sharkey clay. We conclude that adding poultry litter to these alluvial soils will increase metolachlor adsorption and further increase rates of degradation. However, appropriate amounts of poultry litter when applied, are promising for enhancing remediation of metolachlor.