Increasing soil organic carbon pools and wheat yields by optimising tillage and fertilisation on the Loess Plateau in China

The effect of conservation tillage on soil organic carbon (SOC) sequestration and crop production is controversial in semi-arid areas. In addition, fertilisation is another essential factor affecting soil carbon pool and crop yields. We sought to explore the changes of SOC pool and crop productivity after optimising fertilisation and tillage. An 11-year field experiment on the Loess Plateau in China was conducted to evaluate the effects of (i) fertilisation (balanced fertilisation, low fertilisation, conventional fertilisation) and (ii) tillage (no-tillage, subsoiling, ploughing) on input-C, SOC stocks, labile C fractions, C pool management index (CMI) and wheat yield. SOC stock accumulation at 0-35 cm depth under balanced fertilisation increased by 59% compared to conventional fertilisation due to the larger amount and stabilisation efficiency of input-C. Simultaneously, balanced fertilisation increased labile C contents and CMI at 0-10 cm depth. For tillage, no-tillage and subsoiling improved input-C and its stabilisation efficiency, and increased SOC stocks compared to ploughing. Balanced fertilisation combined with no-tillage or subsoiling produced greater SOC stocks at 0-35 cm depth compared to other treatments. No-tillage increased labile C contents and CMI at 0-10 cm depth, while subsoiling increased labile C contents and CMI at 0-10 and 35-50 cm depths. Wheat yield and sustainable yield index (SYI) were positively correlated with SOC, and the effect of SOC contributed to SYI largely through indirect effects of dissolved organic C and particulate organic C. Wheat yield and SYI were increased by optimising fertilisation and tillage, and the greatest yield was under balanced fertilisation combined with the subsoiling treatment. Our findings suggested that balanced fertilisation combined with subsoiling was an effective practice for increasing SOC sequestration, soil quality, wheat yields and had great potential application on the Loess Plateau in China. Highlights C sequestration under conservation tillage and fertilisation are controversial in semi-arid areas. Balanced fertilisation promoted SOC sequestration in no-tillage and subsoiling treatments. Subsoiling improved soil quality at 0-10 and 35-50 cm depths due to the greater SOC and labile C. Subsoiling was superior to no-tillage and ploughing in maintaining crop productivity.