Reducing Nitrogen Loss with Managed Drainage and Polymer-Coated Urea

Continuous corn (Zea mays L.) production during dry years combined with high N fertilizer rates can have a high potential for NO3 (-)-N loss through tile drainage water. Claypan soils can further increase the potential for NO3 (-)-N loss through tile drainage water due to the claypan layer that restricts N leaching below the tile drains. The objective of this 4-yr study was to determine whether use of managed subsurface drainage (MD) in combination with a controlled-release N fertilizer could reduce the annual amount of NO3 (-)-N loss through tile drainage water compared with free subsurface tile drainage (FD) with a noncoated urea application. Due to dry conditions over the summer and fall months, MD reduced the annual amount of water drained by at least 73% compared with FD in two of the four crop years. Low N loss and reduced corn N uptake possibly resulted in carry-over N and high soil N concentrations throughout the study, which may have limited the effect of N fertilizer source on annual NO3 (-)-N loss in the tile drainage water. Use of MD reduced annual NO3 (-)-N loss in the tile drainage water by 78 to 85% in two of the four years. High NO3 (-)-N loss reduction with MD compared with FD was largely due to dry growing season conditions in combination with wet conditions over the noncropping period.