Nitrate-Nitrogen Losses through Subsurface Drainage under Various Agricultural Land Covers

Nitrate-nitrogen (NO3-N) loading to surface water bodies from subsurface drainage is an environmental concern in the midwestern United States. The objective of this study was to investigate the effect of various land covers on NO3-N loss through subsurface drainage. Land-cover treatments included (i) conventional corn (Zea mays L.) (C) and soybean [Glycine max (L.) Merr.] (S); (ii) winter rye (Secale cereale L.) cover crop before corn (rC) and before soybean (rS); (iii) kura clover (Trifolium ambiguum M. Bieb.) as a living mulch for corn (kC); and (iv) perennial forage of orchardgrass (Dactylis glomerata L.) mixed with clovers (PF). In spring, total N uptake by aboveground biomass of rye in rC, rye in rS, kura clover in kC, and grasses in PF were 14.2, 31.8, 87.0, and 46.3 kg N ha(-1), respectively. Effect of land covers on subsurface drainage was not significant. The NO3-N loss was significantly lower for kC and PF than C and S treatments (p < 0.05); rye cover crop did not reduce NO3-N loss, but NO3-N concentration was significantly reduced in rC during March to June and in rS during July to November (p < 0.05). Moreover, the increase of soil NO3-N from early to late spring in rS was significantly lower than the S treatment (p < 0.05). This study suggests that kC and PF are effective in reducing NO3-N loss, but these systems could lead to concerns relative to grain yield loss and change in farming practices. Management strategies for kC need further study to achieve reasonable corn yield. The effectiveness of rye cover crop on NO3-N loss reduction needs further investigation under conditions of different N rates, wider weather patterns, and fall tillage.