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Nitrate Losses to Subsurface Drains as Affected by Winter Cover Crop, Fertilizer N Rates, and Drain Spacing

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  701P0304,  . (doi: 10.13031/2013.15712)
Authors:   E.J. Kladivko, J.R. Frankenberger, B. J. Jenkinson, and N.R. Fausey
Keywords:   drainage, tiles, nitrate, water quality, leaching, cover crops

Subsurface tile drainage is a common water management practice in agricultural regions with seasonal high water tables. This paper reports the results of a 16-yr subsurface tile drainage research study on a site located in southeastern Indiana, USA. The site includes three tile 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. Drainflow volumes are continuously recorded and the water is sampled for nitrate-N on a flowproportional basis. Additional field measurements have included soil water content and potential, water table, and crop yield. In general, drainflow and nitrate-N losses per unit area increase as drain spacing becomes narrower. Drainflow removed between 8 and 26% of annual rainfall, depending on the year and drain spacing. Nitrate-N concentrations in the drainflow did not vary with spacing, but concentrations have significantly decreased from the beginning to the end of the experiment. Concentrations dropped from a mean of 28 mg L-1 in the 1986-1988 period, to a mean of 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 course of the experiment and to the addition of a winter cover crop as a trap crop after corn in the corn-soybean rotation. Average annual nitrate-N mass losses dropped from 38 kg ha-1 in the 1986-1988 period, to 15 kg ha-1 in the 1997- 1999 period, and losses were greatest for the narrowest spacing. Most of the nitrate-N losses occurred during the dormant 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.

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