SOIL MANAGEMENT Subsurface Drain Losses of Water and Nitrate following Conversion of Perennials to Row Crops

tificial drainage, however, are well documented and include sediment, nutrient (N, P), and pesticide delivery Nitrate losses through subsurface drains in agricultural fields pose to surface waters via subsurface drain lines (Gast et al., a serious threat to surface water quality. Substantial reductions in drainage losses of NO3–N can occur with alfalfa (Medicago sativa 1978; Logan et al., 1980, 1993; Kladivko et al., 1991; L.) or perennial grasses as used in Conservation Reserve Program Buhler et al., 1993; Randall et al., 1997). Recently, river(CRP) plantings. Conversion of perennials to annual row crops, howborne nutrients, mainly NO3–N from farmland in the ever, could have rapid, adverse affects on water quality. We evaluated Upper Midwest, have been implicated in the spread of water and N use efficiency of row crops following perennials, and hypoxic bottom waters in the Gulf of Mexico near the losses of water and NO3–N to subsurface drains. Four cropping sysmouth of the Mississippi River (Antweiler et al., 1995; tems: continuous corn (Zea mays L.), a corn–soybean [Glycine max Burkhart and James, 1999). A major source of NO3–N (L.) Merr.] rotation, alfalfa (ALF), and CRP, were established in found in the upper Mississippi River is from agricultural 1988. The ALF and CRP were converted to a corn–corn–soybean fields that are artificially drained (Goolsby, 1999). The sequence from 1994 through 1996 while continuous corn (C-C) and contamination of surface and ground waters from sedicorn–soybean (C-S) rotations were maintained. Following CRP, corn yield was 14% and water use efficiency (WUE) 20% greater as comment and land-applied agri-chemicals (CAST, 1985) pared with C-C. Yield was 19% and WUE 21% greater for soybean combined with spreading hypoxia in the Gulf of Mexico following corn in CRP and ALF as compared with C-S. Residual soil raises concerns about the sustainability of annual rowNO3–N (RSN) increased 125% in first year corn following CRP and crop production in the Upper Midwest. was 32% greater than C-C by 1996. High N uptake efficiencies of Crop rotation can have a substantial effect on the corn following alfalfa slowed the buildup of RSN, but levels were quantity and quality of water entering subsurface drains. equal to row crop systems after 2 yr. Nitrate losses in drainage water Most investigations in the Midwest have evaluated the remained low during the initial year of conversion, but were similar influence of annual row-crop (e.g., corn and soybean) to row crop systems during the subsequent 2 yr. Beneficial effects of production on nutrient loss via subsurface drains (Gast perennials on subsurface drainage characteristics were largely negated et al., 1978; Logan et al., 1980, 1993; Baker and Johnson, following 1 to 2 yr of corn. 1981; Kladivko et al., 1991; Randall and Iragavarapu, 1995; Randall et al., 1997). These studies concluded that: (i) annual losses of NO3–N through subsurface tile P of annual row crops on large areas of drains are substantial, ranging up to 120 kg N ha21; (ii) poorly drained soils in the Upper Midwest requires NO3–N concentrations of drainage water often exceed artificial drainage to improve timeliness of field operathe USEPA drinking water standard of 10 mg L21; and tions and suitability of the soil environment for annual (iii) NO3–N losses in row-crop systems are dependent crop growth (Wheaton, 1977). Adverse environmental on drain flow volumes and fertilizer N management. In consequences of intensive row-crop production with arcontrast to annual crops, perennial crops such as alfalfa and grass can reduce NO3–N concentrations in the soil D.R. Huggins, USDA-ARS, Land Management and Water Conserv. profile (Mathers et al., 1975; MacLean, 1977; Russelle Res. Unit, 215 Johnson Hall, Washington State Univ., Pullman, WA and Hargrove, 1989; Randall et al., 1997), decrease 99164-6421; G.W. Randall, Univ. of Minnesota Southern Res. and NO3–N concentrations and flux in drainage waters, and Outreach Center, Waseca, MN 56093; and M.P. Russelle, Plant Science Res. Unit, USDA-ARS, U.S. Dairy Forage Research Center, St. Paul, MN 55108-6028. Joint publication of the USDA-ARS and Abbreviations: CRP, Conservation Reserve Program; RSN, residual the Minn. Agric. Exp. Stn. Received 20 Mar. 2000. *Corresponding soil NO3–N; C, corn; S, soybean; ALF, alfalfa; NUE, nitrogen use author ([email protected]). efficiency; PVC, polyvinyl chloride; WUE, water use efficiency; ET, evapotranspiration. Published in Agron. J. 93:477–486 (2001).