Capacity and key drivers for reducing the environmental costs of crop production under future climate scenarios by using green manure

Environmental costs of crop production under different climate scenarios should be quantified to guide farmers and policy makers to develop future-oriented sustainable field management practices. To achieve this goal, leguminous green manures with optimised synthetic nitrogen rates were established as sustainable field management practices, which included Huai bean + 52 kg/ha of synthetic nitrogen (HNO) and soybean + 79 kg/ha of synthetic nitrogen (SNO). Summer fallow + 162 kg/ha of synthetic nitrogen (BAU) was the control. We integrated process-based models and empirical nitrogen leakage models under the representative concentration pathway (RCP) 4.5 and 8.5 to project the environmental costs of wheat production on the Loess Plateau of China. Compared with BAU, HNO and SNO would increase soil organic carbon stocks by 14-18 Mg/ha until 2100, reducing carbon footprints and total environmental costs by 36 %-77 % and 46 %-70 %, respectively. Less than 30 % of the reduced total environmental costs were ascribed to the enhanced soil organic carbon stocks. The compromised carbon sequestration potential under RCP8.5 would increase the total environmental costs during crop production over time. By contrast, >60 % of the reduced total environmental costs were associated with the decreased reactive nitrogen leakage under HNO and SNO because their low synthetic nitrogen application rates compared to BAU. Conclusively, besides enhancing carbon sequestration, replacing synthetic nitrogen with leguminous green manure has an even greater capacity to reduce the environmental costs of wheat production in the future, suggesting this practice could effectively promote environmentally friendly crop production.