Long-term Tile Drainage Studies Provide Data for Better Reduction of Nitrate Leaching Losses.

Rapid growth in the biofuels industry presents opportunities for Midwest agriculture as well as potential threats to water quality in the region.  The combination of potentially more corn acres, potentially higher fertilizer rates due to higher grain prices or premiums, and the intensification of drainage, would suggest a greatly increased risk of excessive nitrate losses from Midwest cropland.  There are few field facilities where one can measure the actual nitrate losses from cropland into tile drainage water.  The long-term (23-yr) drainage and water quality study at the Southeast Purdue Agricultural Center (SEPAC) is one such facility, and it has a wealth of data that contribute to understanding the tradeoffs and possible strategies to reducing nitrate leaching into drainage waters from corn-based systems.   Earlier work at the site had focused on a system of continuous corn, conventional tillage, and relatively high N fertilizer application rates by today’s standards.  More recent work at the site employed a corn-soybean rotation, no-tillage, lower fertilizer N rates, and a winter cover crop after the corn year as a trap crop for residual N.  The field site has now been transitioned into a corn-corn-soybean rotation.  A unique aspect of this study site is the evaluation of different drainage intensities (drain spacings) on hydrology and nitrate losses from the rootzone.  It is one of the only long-term datasets on water and nitrate losses from different drain spacings in the same soil and climate.  Results have clearly documented that greater nitrate losses occur when drain spacing becomes narrower, which in turn underscores the need to consider winter cover crops and other strategies to reduce nitrate loads from areas where drainage intensity is increasing.  The importance of long-term field studies and the implications of the data for future management practices will be discussed.