Effect of crop type and season on nutrient leaching to tile drainage under a corn-soybean rotation

Subsurface tile drainage is a significant pathway for nitrogen (N) and phosphorus (P) transport from agricultural fields. The objective of this study was to evaluate N and P loss through tile drainage under corn (Zea mays L.) and soybean (Glycine max L.) production in a corn-soybean rotation typical of agricultural management across the eastern Corn Belt of the US Midwest. Differences in nutrient concentrations and loadings between crop type and between growing (GS) and nongrowing seasons (NGS) were assessed. From 2005 through 2012, discharge and water quality were monitored at three end-of-tile locations that had estimated contributing areas ranging from 7.7 to 14.9 ha (19.0 to 36.8 ac) in a headwater watershed in central Ohio, United States. Nitrate-N (NO3-N) and dissolved reactive P (DRP) were the primary (> 75%) forms of N and P in drainage water. DRP concentration and loading was not significantly different between crop types, but differed significantly by season. Mean weekly DRP concentration (0.22 mg L-1 [0.22 ppm]) was greater during the GS, while mean weekly DRP load (0.010 kg ha(-1) [0.009 lb ac(-1)]) was greater in the NGS. In comparison, NO3-N concentration and load was dependent on the interaction between crop type and season, with the greatest NO3-N concentration (17.1 mg L-1) observed during the GS under corn production. Differences in N and P loss to tile drains were attributed to the timing of nutrient application and differences in seasonal discharge. Practices such as cover crops and drainage water management that target nutrient transport in the NGS should be explored as a means to decrease annual N and P loads. Adherence to recommended 4R nutrient stewardship (right fertilizer source, right rate, right time, and right placement) practices should also help minimize nutrient leaching to tile drains under a corn-soybean rotation.