Improvement effects of calcium silicate hydrate and humic acid-encapsulated Alcaligenes faecalis on acidic farmland soil and alterations in microbial community structure

Soil acidification poses a critical threat to agricultural safe production by compromising soil fertility. Conventional remediation strategies for acidic soils face persistent challenges including short-lived efficacy, structural deterioration, and secondary pollution risks. This study presents an innovative bioremediation approach utilizing Alcaligenes faecalis ( A. faecalis ), a potent alkaline-metabolizing microorganism, coated by calcium silicate hydrate (CSH) and humic acid (HA) as a biocarrier for acidic farmland soil restoration. Through microcosm experiments and high-throughput sequencing analysis, we demonstrated that the remediation approach achieved remarkable soil pH elevation from an initial 4.66 to 6.41 within 21 d. Soil available nitrogen (AN) and silicon (ASi) contents increased to 252.83–595.70 mg/kg and 89.24-133.57 mg/kg at 21 d, respectively; and available phosphorus (AP) content increased from 15.59–39.88 mg/kg to 20.44–55.98 mg/kg at 7 d. There was a positive correlation between pH and all nutrient indicators for soil samples. Moreover, the restoration could also change the microbial diversity and structure. This led to an increase in the relative abundance of functional genera including Bacillus (from 0.44–0.65% to 4.92–21.89%), Arthrobacter (from 0.13–0.30% to 0.17–16.31%), and Paenochrobactrum (from 0.02–0.04% to 0.75–17.43%) at 5 d. These microorganisms were related to soil nitrogen, phosphorus, and silicon cycling, which were positively correlated with an increase in AN, ASi and AP content in soils. Results highlight the application potential of Alcaligenes faecalis as a biomaterial for soil improvement in acidic farmland, providing a new option for the improvement of acidic soil.