Management practices for control of runoff losses from cotton furrows under storm rainfall. II. Transport of pesticides in runoff

Abstract

Pesticide transport in runoff was measured using a rainfall simulator on cotton hill–furrow systems with a range of on-ground cover (0–60%), each with and without prior wheel traffic. The scenario was a 65-mm storm, 3 weeks after planting cotton with associated herbicide applications and 2 endosulfan applications after planting. Concentrations of α, β, and total endosulfan in runoff decreased significantly with increasing cover, irrespective of cover type (wheat stubble or cotton trash) or placement (in furrow or overall). Concentrations of endosulfan sulfate, trifluralin, and DDE decreased with cover, but were affected by cover placement. With 45–60% cover, concentrations were reduced 5-fold for α, β, and total endosulfan; halved for endosulfan sulfate, trifluralin, and DDE; and unchanged for prometryn. Cover had more effect on endosulfan because cover intercepted and dissipated the sprayed endosulfan, reducing concentrations in surface soil and therefore in runoff. This is a mechanism for reducing pesticide runoff additional to effects of cover on runoff and sediment. Cover placement affected pesticide concentrations because cover in the furrows was more effective in trapping larger sediment than evenly spread cover. Pesticide concentrations (mg/kg) were apparently greater in larger, aggregated sediment than in fines, probably because of more organic matter in larger sediment.

Cover had more effect on total pesticide losses (g/ha) than on concentrations, because cover reduced runoff and soil loss considerably. With 45–60% cover, total losses of α, β, and total endosulfan were 1.4% of losses from bare plots, endosulfan sulfate and DDE 3%, trifluralin 5%, and prometryn 8%. Avoiding wheel traffic gave 20–30% lower concentrations and 40% lower losses, due to lower transport in the water phase and enhanced the effect of cover, but did not prevent large pesticide losses from bare plots. Prometryn was transported mostly in the water phase while other pesticides were transported mostly with sediment. Cover provided more control of more soil-sorbed pesticides (endosulfan, trifluralin, and DDE) due to a large reduction in soil loss with cover. Control of the less sorbed prometryn was largely due to cover reducing runoff.

agricultural chemicals, endosulfan, prometryn, trifluralin, DDE, cover, controlled traffic, water quality.