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Title: WATER TABLE CONTROL EFFECTS ON LEACHING LOSSES OF SOIL-APPLIED HERBICIDES

Author
item Southwick Jr, Lloyd
item WILLIS, GUYE - ARS - RETIRED
item Fouss, James

Submitted to: Irrigation and Drainage International Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/10/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Subsurface drains in an agricultural field increase rainfall infiltration and therefore reduce surface runoff of the rainwater. This runoff reduction leads to diminished runoff losses of soil-applied chemicals such as insecticides and herbicides. Controlling water table depth at a certain level below the soil surface and above the drain lines also can be effective in reducing runoff losses of agricultural chemicals. Water table control provides an additional advantage: leaching into the drain can be greatly diminished, thereby reducing the amount of leachate pumped into a surface waterway. In studies of water table control at 45 and 75 cm below the soil surface we have observed reductions of water flow into the drains of 30% compared to the leaching into the drains without water table control. This decreased water flow has translated into corresponding, but not as great, reductions of applied herbicide flow into the drains. In these studies, therefore, the water table control procedure is showing promise as a method of keeping leached herbicides in the soil profile for continued herbicidal activity and for soil degradation processes. Additional work will involve a dynamic control whereby the water table is adjusted with respect to expected rainfall in order to maintain a desirable balance between runoff losses and leaching of applied chemicals.

Technical Abstract: The effect of water table management on leaching losses of atrazine and metolachlor was investigated for 91 days after chemical application in a field study on Mississippi River alluvial soil (Commerce silt loam). Water flow into the subsurface drains (1 m deep) from plots with water table management at 45 cm (CWT45) or 75 cm (CWT75) below the soil surface was about one third that from plots with traditional uncontrolled subsurface drainage (DRN)--a statistical difference. The concentrations of the two herbicides in the drain outflow did not show the same trend as water flow, so that total leaching losses of the chemicals, although less from the CWT45 and CWT75 treatments, were not statistically lower than that from the DRN plots. Additional studies are planned in which water tables are controlled with respect to predicted and actual rainfall.