The effects of tillage practices on the soil organic carbon content and the CO2 distribution in the maize canopy in saline‒alkali cropland areas

Context. Saline‒alkali cropland exhibits high soil salinity and low carbon content levels, leading to deterioration in soil physical and chemical properties. Aims. This study aimed to test the effects of tillage methods on soil organic carbon (SOC) functional groups and the CO2 distribution in the maize canopy. Methods. The experimental design used two tillage methods: subsoiling (ST) and rotary tillage (RT). The physical and chemical properties of soil, as well as the CO2 concentration in the canopy, were analyzed during the anthesis, filling, and mature stages of maize. Key results. In the 0–20 cm soil layer, the salt, total carbon, SOC, inorganic carbon (SIC), alkyl carbon, and alkoxy carbon contents under RT increased by 2.67%, 8.36%, 9.78%, 7.47%, 14.41%, and 2.85%, respectively, compared with those under ST. Compared with those under RT, the aromatic carbon and carboxyl carbon contents under ST increased by 26.13% and 5.95%, respectively. In the 20–40 cm soil layer, the soil salt, alkyl carbon and alkoxy carbon contents under RT increased by 1.29%, 24.04% and 5.10%, respectively, compared with those under ST. Compared with those under RT, the total carbon, SOC and SIC, aromatic carbon and carboxyl carbon contents under ST increased by 12.97%, 3.48%, 4.87%, 36.79% and 9.45%, respectively. There was a positive correlation between the total carbon, SOC and SIC contents. The CO2 concentration at the middle of the canopy was greater than that at both ends. At the anthesis and filling stages, the δ13CO2 value decreased with increasing canopy height but slightly increased at the 150-cm height. Conclusions. Overall, compared with RT, the implementation of ST increased the SOC level, facilitated soil acidity and alkalinity regulation. Implications. Our research results can guide the improvement of saline-alkali land and create a more favourable soil environment for crop growth.