Co-incorporating rice straw and Chinese milk vetch (CMV) residues can enhance soil organic carbon (SOC) sequestration and productivity. However, limited information exists regarding its effects on SOC and nitrogen (N) pools as well as the sustainability of rice production in the middle and lower reaches of the Yangtze River Basin. A 3-year field experiment was conducted to assess the effects of co-incorporating rice and CMV residues into paddy soils with chemical-N reduction on SOC and total N (TN) sequestration, SOC and N fractions, grain yields and the sustainable yield index (SYI) in Ma’anshan City, Anhui Province. The treatments included winter fallow–rice rotation without or with both rice straw incorporation and fertilization, as the control (CK and WF-IF, respectively), and rice-CMV rotation with the co-incorporation of rice and CMV residues under 100%, 80%, and 70% recommended N fertilization (CMV-IF, CMV-MIF and CMV-LIF, respectively). Compared with the CK, the CMV-IF significantly increased the rice grain yield and the SYI by 82.1% and 90.4%, respectively. The SOC and TN stocks under CMV-IF were significantly enhanced by 6.3% and 26.4%, respectively, relative to the CK. The CMV-IF exhibited the highest soil active organic C (AOC) and active total N (ATN) contents, followed by CMV-MIF, CMV-LIF, WF-IF, and CK. Microbial biomass C and microbial biomass N were the primary components of soil AOC and ATN, respectively, and linked more explicitly to the SYI than other soil C and N parameters. Therefore, the co-incorporation of rice and CMV residues, coupled with 70~80% recommended N fertilization, might represent an environmentally friendly field management practice for rice production in the middle and lower reaches of the Yangtze River Basin.

Optimizing tillage and fertilization practices is of vital importance for enhancing soil carbon retention, improving soil quality and increasing crop productivity in the intensive wheat (Triticum aestivum L.)–maize (Zea mays L.) double cropping system (WM). However, the combined effects of subsoiling (ST) and liquid manure (LM) application on yield sustainability and the dynamic changes in labile organic carbon (LOC) fractions (LOCs) remain insufficiently quantified in WM in the North China Plain (NCP). A two-year field experiment evaluated the responses of grain yields, the sustainable yield index (SYI), soil organic carbon (SOC), LOCs, C pool management indexes (CPMIs), and the soil quality index (SQI) to both patterns of tillage [conventional shallow rotary tillage (RT) and ST] and fertilization [conventional fertilization (CF), LM broadcast (LMB), and LM injection (LMI)] in WM in the NCP. Compared with RT, ST significantly enhanced crop grain yields (3.5~4.1%) and the annual SYI (4.1%) (p < 0.05). The contents of SOC, total labile OC (TLOC), high LOC (HLOC), and medium LOC (MLOC) and the values of SQI were higher in soil layers at both 0–20 cm and 20–40 cm under ST than those under RT. Compared with CF, LMI significantly enhanced grain yields (5.8~6.1%) and the annual SYI (5.4%). LMI significantly increased the contents of SOC, TLOC, HLOC, and MLOC and the SQI values in both soil layers relative to CF, while no significant difference was observed for grain yields, the annual SYI, and the SQI between LMB and CF. The higher contents of SOC and LOC led to an increase in the values of CPMIs based on TLOC (TCPMI), HLOC (HCPMI), and MLOC (MCPMI). The combination of both ST and LMI enhanced SOC retention through the increase in recalcitrant organic carbon (ROC) content and the transformation process of LOCs. It was obvious that HLOC and MLOC affected SOC, HCPMI, and MCPMI in the soil layers at both 0–20 cm and 20–40 cm, and thus can be regarded as sensitive indicators reflecting the dynamic changes in SOC and soil quality. Therefore, the combination of subsoiling and liquid manure injection can promote labile OC transformation, SOC retention, soil quality, and yield sustainability, providing an effective management strategy for the achievement of sustained agricultural production in the NCP or other regions with similar conditions.