There is a need to explore management practices that reduce nitrate (NO3-) leaching and aid in meeting current greenhouse gas reduction goals. Tile drainage involves using perforated pipes to remove excess subsurface water from agricultural fields, also removing nutrients. The inclusion of cover crops in tile -drained systems in the Midwest has been shown to reduce NO3 - losses and is potentially a strategy to mitigate soil nitrous oxide (N2O) emissions. The objectives of this research were to 1) evaluate cumulative soil NO3 - and soil N2O losses with and without the inclusion of cover crops in a corn -soybean rotation on a tile -drained landscape and; 2) assess the environmental damage cost (EDC) of N losses with and without the inclusion of cover crops in a corn -soybean rotation on a tile -drained landscape. Corn (Zea mays L.) was grown in 2017, and soybean (Glycine max L.) in 2018. The cover crop used in this experiment was a 92% cereal rye (Secale cereal L.) and 8% daikon radish (Raphanus sativus L.) blend. Treatments included cover crop inclusion, no cover crop inclusion, and a zero control, which did not include cover crops or receive N fertilization. Each treatment was replicated three times in individually tile -drained plots established in Lexington, IL during the 2017 and 2018 growing seasons. In 2017, cover crop inclusion led to a reduction in NO3- losses of over 50% when compared to the no cover and zero control. In 2018, total N losses were identical; however, there was an increase in soil N2O emissions across all treatments compared to 2017. Despite the apparent tradeoff between N loss pathways in 2018, the overall EDC was reduced primarily because of the reduction in NO3 - loss in the presence of cover crops. The results of this study indicated that the inclusion of a cover crop resulted in a sizeable reduction in N loss during the corn year that equated to a 64% reduction in EDC across a two-year crop rotation.

Reactive nitrogen (Nr) pollution has changed radically accompanied by severe intensive farming. This pollution further contributes to ecological degradation and climate warming. Despite this recognition, little is known about the spatial pattern of various Nr loss from croplands and corresponding environmental costs. Here, we identified the major pathway of Nr loss based on provincial estimates in 2008 and 2018, and validated by synchronous observation of ammonia volatilization, N runoff and N leaching using historical literature synthesis. We also evaluated environmental costs at provincial scale and detected the influence factors that dominating the pollution swapping among different Nr forms. Our results show that the total Nr loss was 6.28 +/- 1.81 and 5.56 +/- 2.30 Tg N yr(-1) for Chinese croplands in 2008 and 2018. Ammonia volatilization, which accounted for more than half of the total Nr at the national scale, was proven to be the major Nr loss for two-thirds of the provinces and 80 % of the field observations. The contribution of runoff, which is dominant by precipitation, soil clay content and CEC, was gradually smaller than that of leaching from southeast to northwest. Ammonia and nitrous oxide contributed of 59.3 % - 65.4 % of TNr but 80.9 % - 81.5 % of total environmental damage caused by Nr in China. The use of nitrification inhibitors and straw return indicated pollution swapping among various Nr forms. This study emphasizes that the future practices to reduce total Nr loss need to account for local environmental conditions and have pollution swapping in sights.