| This dissertation includes the study of hydrologic cycling and nitrogen dynamics under various land covers for the subsurface drained agriculture in Iowa through field investigation and modeling approaches. Land covers included conventional corn-soybean rotation, winter rye cover crop in corn-soybean rotation, kura clover as a living mulch for corn, and perennial forage. Field experiments consisted of two parts: one was conducted in a crop field at a plotscale including all the land covers near Gilmore City, Iowa from 2006 to 2008 and the other was conducted in non-weighing lysimeters with winter rye cover crop and bare soil during 2006-2008. The RZWQM-DSSAT model was tested against the measured data from the plotscale study and the evaluated model was subsequently used to simulate the long-term impacts of winter rye cover crop on hydrologic cycling and nitrogen dynamics. Overall, the results suggest that subsurface drainage water quality in terms of NO3-N contamination can be effectively improved by converting conventional corn-soybean rotation into perennial forage, but at present there would be little economic return for the grasses and it may also alter the local hydrologic cycle. Planting corn in established kura clover living mulch also reduced the annual flow-weighted NO3-N concentration and NO3-N loss in the subsurface drainage flow, but the corn yield in kura clover treatment was significantly reduced. Although not significantly impacting total NO3-N loss in the plot-scale study, rye significantly reduced the NO3-N concentration in soil water within the soil profile, and showed a potential in reducing subsurface drainage and NO3-N loss in the non-weighing lysimeter and the long-term simulation studies. Therefore, rye cover crop has the potential to be an excellent cropping option under an integrated concern for the environment and economy. |
