NITRATE LEACHING TO SUBSURFACE DRAINS AS AFFECTED BY DRAIN SPACING AND CHANGES IN CROP PRODUCTION SYSTEM

Authors: KLADIVKO, E - PURDUE UNIVERSITY; FRANKENBERGER, J - PURDUE UNIVERSITY; Jaynes, Dan; Meek, David; JENKINSON, B - PURDUE UNIVERSITY; Fausey, Norman

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2004
Publication Date: 9/15/2004
Citation: Kladivko, E.J., Frankenberger, J.R., Jaynes, D.B., Meek, D.W., Jenkinson, B.J., Fausey, N.R. 2004. Nitrate Leaching to Subsurface Drains as Affected by Drain Spacing and Changes in Crop Production System. Journal of Environmental Quality. 33(5):1803-1813.

Interpretive Summary: Subsurface tile drainage is a common water management practice in much of Indiana and the Midwest. Although subsurface drainage has many benefits (greater infiltration, lower surface runoff, improved crop growth and yield), it also may increase nitrate-nitrogen (N) losses through the rootzone and out to surface waters. An appropriate balance between increasing drainage intensity (narrower spacing) to improve drainage and decreasing drainage intensity to reduce nitrate-N losses needs to be found for different climatic and soil regions. We measured nitrate leaching into tile drains of three different spacings (drainage intensities) at a long-term research site in southeastern Indiana. Over the 15-year period, we sequentially changed management practices in an attempt to reduce nitrate leaching from the rootzone. Nitrate concentrations and total losses in the tile drains have decreased significantly as a result of adding soybean rotation, reducing fertilizer N rates, and including a winter cover drop after corn to "trap" some of the soil nitrogen in late fall through early spring, when much of the water drainage occurs. Our results show that at least on low organic matter, silt loam soils, concentrations of nitrate in tile drainage can be reduced to below the drinking water limit, by a combination of lower fertilizer N rates and a winter cover crop after corn in a corn-soybean rotation. The results are promising for concerns about nitrate contributions to surface waters in the Mississippi River basin and their potential impact on hypoxia in the Gulf of Mexico and will be of interest to farmers, NRCS and other action agencies, and state and federal regulators.

Technical Abstract: Subsurface drainage is a beneficial water management practice in poorly drained soils but may also contribute substantial nitrate-nitrogen (N) loads to surface waters. This paper summarizes results from a 15-year drainage study in Indiana that includes three drain spacings (5, 10, and 20 m) managed for 10 years with chisel tillage in monoculture corn (Zea mays L.) and currently managed under a no-till corn-soybean (Glycine max L.) rotation. In general, drainflow and nitrate-N losses per unit area were greater for narrower drain spacings. Drainflow removed between 8 and 26% of annual rainfall, depending on year and drain spacing. Nitrate-N concentrations in drainflow did not vary with spacing, but concentrations have significantly decreased from the beginning to the end of the experiment. Flow-weighted mean concentrations decreased from 28 mg L**-1 in the 1986-1988 period to 8 mg L**-1 in the 1997-1999 period. The reduction in concentration was due to both a reduction in fertilizer N rates over the study period and to the addition of a winter cover crop as a "trap crop" after corn in the corn-soybean rotation. Annual nitrate-N loads decreased from 38 kg ha**-1 in the 1986-1988 period to 15 kg ha**-1 in the 1997-1999 period. Most of the nitrate-N losses occurred during the fallow season, when most of the drainage occurred. Results of this study underscore the necessity of long-term research on different soil types and in different climatic zones, in order to develop appropriate management strategies for both economic crop production and protection of environmental quality.