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, soil 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 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 ST. Compared with RT, the total carbon, SOC, SIC, aromatic carbon, and carboxyl carbon contents under ST increased by 12.97%, 3.48%, 4.87%, 36.79%, and 9.45%, respectively. There were positive correlations among the total carbon, SOC, and SIC contents. The CO2 concentration within 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 150-cm canopy height. Conclusions Overall, compared with RT, implementation of ST increased the SOC level and 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.