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Title: INFLUENCE OF WATER TABLE MANAGEMENT ON RUNOFF LOSSES OF SOIL-APPLIED PESTICIDES

Author
item Southwick Jr, Lloyd
item Willis, Guye
item Fouss, James
item ROGERS, JAMES - RETIRED USDA-ARS
item CARTER, CADE - RETIRED USDA-ARS

Submitted to: Mississippi Water Resources Research Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/17/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: It well known that subsurface drain pipes lower runoff losses of soil and agricultural chemicals from crop lands. Subsurface drains with added ability to control the water table level at a certain depth below the ground surface have a potential advantage of accomodating a preselected volume of rainfall in the soil profile before surface runoff occurs. The present report describes a study of runoff losses of three herbicides and one insecticide from plots planted to corn. The plots with subsurface drains all produced decreases in runoff losses of eroded soil and the pesticides. The various subsurface drain treatments produced similar results. The subsurface drain treatments produced a greater reduction of soil erosional losses than of water runoff losses. Consequently, the losses of pesticides that are adsorbed to the soil in a runoff event are reduced to a greater extent by subsurface drains than are the losses of those chemicals that leave a field in runoff mostly in the water phase. Additional study seasons are planned in order to adequately test the utility of controlling the water table for limiting losses of soil-applied chemicals into surface water bodies. Successful implementation of such technology can lead to the environmentally safer use of agriculturally important chemicals.

Technical Abstract: A field study using sixteen 0.21 ha plots was conducted on alluvial soil in south Louisiana to determine the affect of water table management on runoff losses of atrazine, metolachlor, pendimethalin, and chlorpyrifos. The water management treatments were replicated four times and consisted of the following: SUR: surface drainage only; DRN: conventional subsurface drainage at 1.2 m depth; CWT45: water table held at 45 cm below the soil surface; CWT75: water table held at 75 cm. The subsurface drain treatments all produced decreases in runoff losses of the pesticides, compared to the SUR treatment. Generally, the DRN and CWT45 treatments produced similar reductions in runoff losses. The CWT75 treatment did not perform as well in runoff reduction. The treatment effects were generally not significant, due at least in part to a low runof volume of a subnormal rainfall season. The DRN and CWT75 treatments showed an enhanced effect on losses of pendimethalin and chlorpyrifos (water solubility < 3 mg/L) compared to those of atrazine and metolachlor (water solubility > 3 mg/L). This difference corresponded to a larger reduction in soil erosional losses than in water runoff losses produced by these two treatments, thereby affecting to a greater extent the two compounds of low water solubility. Additional study seasons are planned in order to adequately test the utility of controlled water table for limit losses of soil-applied chemicals into surface water bodies.