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Title: Water Table Control Systems

Author
item Fouss, James
item EVANS, ROBERT - NORTH CAROLINA STATE U
item Ayars, James
item CHRISTEN, EVAN - CSIRO LAND AND WATER

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 9/26/2006
Publication Date: 10/5/2007
Citation: Fouss, J.L., Evans, R.O., Ayars, J.E., Christen, E.W. 2007. Water Table Control Systems. Book Chapter. Design and Operation of Farm Irrigation Systems, 2nd edition; Published by the American Society of Agricultural and Biological Engineers (ASABE); Eds., G.J. Hoffman, R.G. Evans, M.E. Jensen, D.L. Martin and R. L. Elliott. Chapter 18, pp. 684-724. August 2007. ISBN: 1-892769-64-6.

Interpretive Summary: Water table control systems for agricultural cropland are installed primarily to reduce or eliminate the effects of excess and/or deficit soil-water conditions in the root-zone that limit crop yields, and to control losses of applied fertilizers and pesticides (agrochemicals) in subsurface drainage effluent and surface runoff. Water table depth in the soil is maintained within a desired range by controlling subsurface drainage outflow and by subirrigation (i.e., water supplied back through the drainpipes into the soil profile). The primary system design objectives are to improve: (1) Crop production by decreasing the duration of excess and deficit soil-water conditions in the root-zone; and (2) Water quality of drainage effluent by controlling subsurface drainage to decrease outflow volume and thus reduce agrochemical losses. The system should provide control of the water table within the range of soil depth needed for conducting farm field operations for the crops grown, and an operation method to reduce agrochemical losses. In determining optimum drain depth and spacing, it is often not clear whether the greatest demands on the water table control system will be drainage management under wet season shallow water table conditions, or subirrigation needs during extended dry periods. Therefore, a computer simulation model approach is recommended (e.g., with DRAINMOD ver. NII) to conduct a complete design evaluation for the water table control system, and to predict its performance over a period of 10 to 30 years for the climatologic conditions at the specific site. DRAINMOD-NII can predict the effects of system design and operational parameters on the losses of various forms of nitrogen within the soil profile and in subsurface flow and surface runoff. Additionally, an economic analysis for operating the designed system needs to be conducted for the farmer’s use in evaluating the benefits of installing the water table control system on his farm.

Technical Abstract: Water table control systems for agricultural cropland are installed primarily to reduce or eliminate the effects of water related factors that limit crop production, and to control losses of applied agrochemicials in subsurface drainage discharge and surface runoff. System design objectives are to improve: (1) Crop production by controlling the durations of excessive and deficient soil-water conditions in the root-zone; and (2) Water quality of drainage discharge by controlling drainage flow volume to reduce agrochemical losses. An integrated design includes determining the suitability of a site, the required drain depth and spacing, a field installation plan, and method of operation for controlled-drainage and subirrigation modes. The design should provide control of the water table depth in the soil over the range needed for conducting farm field operations for the crops to be grown, and an operation method to reduce agrochemical losses. The design should also provide for efficient utilization of shallow groundwater supplied by natural rainfall or irrigation. In determining optimum drain depth and spacing, it is often not clear whether the greatest demands on the system will be drainage management under wet season shallow water table conditions, or subirrigation needs during extended dry periods. Therefore, a simulation model approach is recommended (e.g., with DRAINMOD ver. NII) to conduct a complete design evaluation analysis for the water table control system, and to predict its performance over a period of 10 to 30 years for the climatologic conditions at the specific site. DRAINMOD-NII can predict the impact of system design and operational parameters on transport of various forms of nitrogen within the soil profile and losses in subsurface flow and runoff. An economic analysis from operating the designed water table control system needs to be conducted for the farmer’s use in evaluating the benefits of installing the system on his farm.