Farm-scale practical strategies to reduce carbon footprint and emergy while increasing economic benefits in crop production in the North China plain

How to achieve China's “Carbon Peak” and “Carbon Neutrality” targets in the agriculture sector is crucial but still remains challenging. This study thus aims to assess the effects of crop rotations and farm size with optimized nitrogen (N) rate on carbon footprint (CF), emergy and economic benefits to promote agricultural transformation in the North China Plain (NCP) based on 792 on-farm questionnaires. Our results showed that the CF and emergy of wheat (Triticum aestivum Linn.)-soybean (Glycine max (Linn.) Merr.) was 32–45% and 20–21% lower than that of wheat-maize (Zea mays Linn.) and wheat-peanut (Arachis hypogaea Linn.) mainly due to reduced N application by the biological nitrogen fixation (BNF) and pre-crop effects of soybean, while the farming net income (FNI) was lowest in the wheat-soybean mainly because of the low soybean yield. Furthermore, the sustainability performance index (SPI) was highest for wheat-soybean while lowest for wheat-maize. Large-size farms (LF, larger than 3.3 ha) efficiently reduced N rate without negatively influencing crop yield, thus decreasing CF and emergy compared to smallholders (SF, smaller than 3.3 ha), and the total farming profit was much higher in the LF due to the scale effect. Our results indicated that the joint application of increased soybean planting area in concert with larger farm size using optimized N rate was beneficial for reducing CF and emergy, but also increasing crop production in the NCP. However, low soybean yield was the critical factor that constrained soybean planting area in the NCP. We suggest that practical, cost-effective strategies to increase soybean yield with concurrent financial subsidies are urgently required to maximize the eco-benefits of wheat-soybean rotation in promoting agricultural green development in the NCP.