Drivers of soybean-based rotations synergistically increase crop productivity and reduce GHG emissions

Soybean-based rotations have long proven beneficial for increasing subsequent crop productivity and nitrogen (N) use efficiency (NUE) under low chemical N inputs. Despite this, importance of soil microbial community and enzymes in N cycling processes has not been well investigated. As well, optimal fertilizer-N that achieve high yield and NUE with low GHG emissions remain uncertain, as perceived "optimal" fertilization varies widely across agroclimatic regions, seasons and production systems. Here, our systematic review indicated that soybean-based rotations mitigate soil-borne diseases, such as cyst nematodes, and thus contribute to increased soybean yield. We show that soybean roots produce large amounts of root exudates, which are conducive to formation of soil macroaggregates and carbon accumulation, enhancing soil health and productivity of gramineous crops. Biological N fixation (BNF) and rhizosphere N deposition of soybean crops together evoke high soil N content and low C:N ratio. We found that soybean-based rotations significantly alleviated acidification and positively influenced soil microbial activities and enzyme activities, reducing N2O and CO2 emissions. Our study demonstrates that reduced fertilizer N inputs catalyse greater BNF and pre-crop effects of soybean in rotations. We provide compelling dialogue that underlines the biological, environmental and economic implications of soybean crops for long term sustainability in farming systems.