Long‐term conservation tillage practices affect total carbon and contribute to the formation of soil aggregates in the semi‐arid North China Plain

Abstract The soil aggregates characteristics and organic carbon (SOC) distribution under various tillage practices have been widely studied, but the changes in inorganic carbon (SIC) and their effect on soil aggregate formation are not clear. This study evaluated how long‐term tillage affects total carbon (both organic and inorganic) and contributes to forming aggregates in a fluvo‐aquic soil derived from limestone alluvial fans in the North China Plain. The four tillage practices that were used in a maize ( Zea mays )/wheat ( Triticum aestivum ) double‐cropping system were moldboard plough without residues (CK), moldboard plough with residue retention (CT), rotary tillage with residue retention (RT) and no tillage with residue retention (NT). CT treatment, compared with NT treatment, decreased the SIC concentration at 0–300 mm and SOC concentration at 0–50 mm but increased the SOC concentration at 100–300 mm. Thus, there were no differences in the total carbon storage in the 0–300 mm layer because of the changes in SOC and SIC concentrations among four tillage practices. NT and RT practices increased the large macro‐aggregates (LM >2mm ) and the mean weight diameter (MWD) only within the 0–50 mm layer, while the CT practice increased the LM >2mm and the MWD within the 100–250 mm layer. Correlation analysis revealed a significant link between LM >2mm and SOC, while small macroaggregates (SM 0.25–2mm ) were closely correlated with SIC. SOC and SIC had a relay cementation effect on the formation of large aggregates under long‐term tillage, and therefore, the effects of these two types of carbon should be comprehensively considered in the study of carbon sequestration and aggregate formation in calcareous soil.