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Title: CONTROLLED WATER-TABLE DEPTH TO IMPROVE WATER QUALITY

Author
item Willis, Guye
item Southwick Jr, Lloyd
item Fouss, James
item Rogers, James
item Carter, Cade

Submitted to: Mississippi Water Resources Research Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/24/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Water table management may be a means for decreasing agrochemical losses in runoff and leaching on high-water-table soils where large amounts of agrochemicals are used and rainfall is frequent. Controlled subdrainage and subirrigation in soils where subsurface drainlines have been installed provide a method for manipulating water tables. Thus, if rain appeared imminent soon after agrochemical application to the soil surface, the water table could be lowered to enhance infiltration and increase within-soil storage capacity, thereby decreasing runoff loss. Alternatively, if pesticide or fertilizer were already incorporated into the soil, the water table could be raised to just below the root zone to retard leaching and thereby retain the chemical in the biologically active root zone longer for utilization or degradation. Water table management treatments (conventional subsurface drainage at 1.2 m below the soil surface, or controlled static water tables at depths of 45 or 75 cm below the soil surface) were applied to 0.2-ha corn plots in southern Louisiana. Preliminary results for the first 18 days after herbicide application (128 mm of rain) show that conventional subsurface drainage and a water table controlled at 45 cm below the soil surface reduced combined runoff and drainage losses for atrazine and metolachlor by about 10 to 15% compared to no subsurface drainage.

Technical Abstract: Four water-table management treatments had varying effects on surface runoff and leaching losses of atrazine and metolachlor (applied at 1.5 and 1.9 kg/ha, respectively) from 0.21-ha corn plots on a lower Mississippi River alluvial soil. Preliminary data indicate that during the first 18 days after herbicide application surface runoff losses from surface-drained-only (SUR) plots (i.e., no subsurface drainlines) were about 2.4% and 1.1% of the respective amounts applied. Combined runoff and leaching losses from plots with conventional subsurface drainage at 1.2 m below the soil surface (DRN) or controlled water table at 45 cm below the soil surface (CWT-45) were reduced by about 10 to 15%, compared to the SUR plots. Combined runoff and leaching losses from plots with a controlled water table at 75 cm (CWT-75) from the soil surface were equal to or greater than losses from the SUR plots. Atrazine losses in subdrainage effluent from the DRN and CWT-75 plots were 0.9% and 1.3%, respectively, of the amount applied. Analogous metolachlor subsurface drainage losses were 0.4% and 0.6%. No subsurface drainage losses occurred from the CWT-45 plots for either herbicide. Thus, preliminary data suggest that water table control may offer a useful technique for reducing agrochemical losses from shallow-water-table soils.