Effect of soybean inclusion in cropping systems on productivity, profitability, and carbon footprints: A case study from the Huang-Huai-Hai Plain

The intensive wheat-maize (W-M) rotation in the Huang-Huai-Hai Plain faces ecological challenges. Introducing legumes into cropping systems is a promising strategy for sustainability, but its effect on productivity and profitability remains uncertain. A two-year experiment examined the effects of three double-cropping systems (Wheat-Soybean, W-S; Wheat with an intercrop of Maize and Soybean, W-M/S; and W-M) on productivity, energy balance, carbon footprint (CF), economic returns, and sustainability. Results showed that, compared to W-M, the pre-crop effect of soybean in W-S and W-M/S increased subsequent wheat yield by 8.8 % and 3.6%, respectively; W-M/S improved annual yields of grain, maize equivalent, and energy by 3.6%, 17.5%, and 6.7%, whereas W-S decreased them by 28.6%, 5.3%, and 25.2%; due to lower inputs, W-S reduced CFs by 19.8%–42.8%; with higher yields and soil organic carbon storage, W-M/S increased net energy, return, and carbon by 5.1%, 9.4%, and 4.3%, while reducing CFs by 19.3%–31.3%, resulting in a 43.2% rise in the sustainability index. In summary, introducing soybeans into cropping systems—either as an intercrop or in rotation—can maintain soil organic carbon and reduce CFs. Moreover, W-M/S can enhance productivity and profitability, making it a more sustainable, efficient, and cleaner system for the Huang-Huai-Hai Plain.