Conservation tillage enhances both organic and inorganic carbon in dryland: Insights from a 20-year field experiment and meta-analysis

Conservation tillage is widely recognized as a promising practice for sequestering soil organic carbon (SOC). However, its impact on soil inorganic carbon (SIC) remains less understood and has seldom been quantified. This study aimed to examine the effects of conservation tillage on soil carbon pools, focusing on SIC, by combining a 20-year field experiment in an arid-calcareous cropland of China with a meta-analysis of 76 pairwise data from 7 studies. The field experiment confirms that conservation tillage significantly increases carbon stock, with reduced tillage (RT) increasing SOC (25.09 %, 0–40 cm) and no-tillage (NT) increasing SIC (10.67 %, 0–20 cm). SOC and SIC exhibit a complementary relationship, whereby an increase in SOC effectively compensates for reduced SIC within RT. Notably, the proliferation of calcifying bacteria (e.g., Bacillus) and reduced urease activity suggest that microbial-induced carbonate precipitation, a process known to be facilitated by these bacteria, may contribute significantly to SIC formation under NT. Agronomic practices, as well as soil abiotic and biotic factors, collectively influence SIC. The relative importance of these factors varies with soil depth: biotic variables effects weaken with depth, while abiotic variables increase. Furthermore, our meta-analysis reveals that the response of SIC to conservation tillage varies with climatic, edaphic, and agronomic factors. Arid regions benefit the most from NT in enhancing SIC stock (3.27 %). These findings provide valuable insights into how conservation tillage influences soil carbon, particularly SIC, and enhance our understanding of carbon dynamics in arid systems.