Effects of tillage rotation modes on soil carbon sequestration and carbon pool management index of farmland in northern Henan

To explore the effects of different tillage rotation modes on soil carbon sequestration and carbon pool management index of farmland in northern Henan, a field experiment comprising five treatments with different tillage modes was carried out during wheat seasons from 2016 to 2020 in fluvo-aquic soil in northern Henan. The treatments were: 1) continuous rotary tillage (RT-RT-RT, CK); 2) deep tillage-rotary tillage-rotary tillage (DT-RT-RT); 3) deep tillage-rotary tillage-shallow rotary tillage (DT-RT-SRT); 4) deep tillage-shallow rotary tillage-shallow rotary tillage (DT-SRT-SRT); 5) deep tillage-shallow rotary tillage-rotary tillage (DT-SRT-RT). Soil bulk density, soil organic carbon (SOC), liable organic carbon (LOC), non-liable organic carbon (NLOC), organic carbon storage, and carbon pool management index (CPMI) in 0–50 cm soil layers were measured and analyzed. The results showed that the soil bulk density in the 0–40 cm soil layer decreased under rotation tillage treatments. In the 0−20 cm soil layer, the SOC, LOC, and NLOC contents, with values of 11.54 g∙kg⁻¹, 3.31 g∙kg⁻¹, 8.30 g∙kg⁻¹, respectively, were the highest under DT-SRT-SRT and were significantly higher than those under RT-RT-RT. Compared with those under RT-RT-RT, the SOC, LOC and NLOC contents in the 10−40 cm soil layer were significantly higher under DT-SRT-RT. The rotation tillage treatments reduced LOC/SOC but increased NLOC/SOC, especially in the 20−40 cm soil layer; the highest increment was 7.5%. During the experimental period, each rotation tillage treatment increased the soil organic carbon storage in the 0−40 cm soil layer. In 2019, the organic carbon storage in the 0−30 cm layer was highest under DT-SRT-SRT (36.64 Mg·hm⁻²). However, the organic carbon storage in the 0−40 cm soil layer, which increased by 12.8% and 9.7%, respectively, during 2019 and 2020 compared with that under RT-RT-RT, and was highest under DT-SRT-RT. In 2019, the activity index of carbon pool in the 0−40 cm soil layer under DT-SRT-RT was reduced. The CPMI was relatively low, with a maximum reduction of 4.3%. In 2020, DT-SRT-RT significantly increased the carbon pool index and CPMI values in the 0−40 cm soil layer; the highest CPMI was 108.5. Generally, deep tillage-strip rotary tillage-rotary tillage reduced soil bulk density; increased contents of SOC, LOC, and NLOC as well as NLOC/SOC value; and increased the organic carbon storage in 0−40 cm soil layer; therefore, it was suggested as the optimum practice for carbon sequestration of farmland in northern Henan.