Reducing Nitrate Loss in Tile Drainage Water with Cover Crops and Water-Table Management Systems

Drury, C. F.; Tan, C. S.; Welacky, T. W.; Reynolds, W. D.; Zhang, T. Q.; Oloya, T. O.; McLaughlin, N. B.; Gaynor, J. D.

Reducing Nitrate Loss in Tile Drainage Water with Cover Crops and Water-Table Management Systems

2014

Nitrate lost from agricultural soils is an economic cost to producers, an environmental concern when it enters rivers and lakes, and a health risk when it enters wells and aquifers used for drinking water. Planting a winter wheat cover crop (CC) and/or use of controlled tile drainage–subirrigation (CDS) may reduce losses of nitrate (NO₃⁻) relative to no cover crop (NCC) and/or traditional unrestricted tile drainage (UTD). A 6-yr (1999–2005) corn–soybean study was conducted to determine the effectiveness of CC+CDS, CC+UTD, NCC+CDS, and NCC+UTD treatments for reducing NO₃⁻ loss. Flow volume and NO₃⁻ concentration in surface runoff and tile drainage were measured continuously, and CC reduced the 5-yr flow-weighted mean (FWM) NO₃⁻ concentration in tile drainage water by 21 to 38% and cumulative NO₃⁻ loss by 14 to 16% relative to NCC. Controlled tile drainage–subirrigation reduced FWM NO₃⁻ concentration by 15 to 33% and cumulative NO₃⁻ loss by 38 to 39% relative to UTD. When CC and CDS were combined, 5-yr cumulative FWM NO₃⁻ concentrations and loss in tile drainage were decreased by 47% (from 9.45 to 4.99 mg N L⁻¹ and from 102 to 53.6 kg N ha⁻¹) relative to NCC+UTD. The reductions in runoff and concomitant increases in tile drainage under CC occurred primarily because of increases in near-surface soil hydraulic conductivity. Cover crops increased corn grain yields by 4 to 7% in 2004 increased 3-yr average soybean yields by 8 to 15%, whereas CDS did not affect corn or soybean yields over the 6 yr. The combined use of a cover crop and water-table management system was highly effective for reducing NO₃⁻ loss from cool, humid agricultural soils.

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