[Liming and biochar effects on soil pH and microbial properties in acidified soils: A meta-analysis]

Soil acidification in agricultural lands has become an increasingly prominent issue, posing a serious threat to soil health. Alkaline amendments is a feasible approach to mitigate acidification, yet their effects on soil microbial properties remain unclear. We conducted a meta-analysis with literature published during 1980 to 2024, to examine the impacts of alkaline materials (lime and biochar) on soil pH, microbial biomass carbon, and microbial diversity in acidified soils. Results showed that both lime and biochar significantly increased soil pH (by 9.1% and 4.4%, respectively), with greater improvements at higher application rates. The strongest effects occurred within 0.25 years after application (19.7% for lime and 9.4% for biochar). Alkaline amendments were the most effective under high temperature (>16 ℃), high rainfall (>1200 mm), and strongly acidic soils (pH≤4.5). Lime and biochar increased microbial biomass carbon by 81.6% and 18.4%, respectively, with the greatest effects observed within 1-2 years. Higher lime application rates (3-6 t·hm^-2·a^-1) produced the strongest improvements, whereas biochar was more effective at lower rates (≤1.5 t·hm^-2·a^-1). Overall, microbial diversity increased by 2.5% following amendment application. Biochar enhanced microbial diversity most strongly within 0.25-0.5 years (14.1%), while lime required more than two years to achieve significant improvement (8.5%). Lime was more effective in low-temperature, low-rainfall regions (up to 6.8%), whereas biochar was better suited to high-temperature, high-rainfall regions (5.5%). Biochar influenced microbial properties indirectly by regulating soil pH, with microbial biomass and diversity showing significant positive correlations with soil pH. In contrast, lime-induced changes in microbial properties were strongly affected by application rate, climatic condition, and initial soil pH. This study clarified the acid-neutralizing effects and soil microbial regulation mechanisms of different alkaline amendments, providing a foundation for further exploration of the coupled physical, chemical, and biological restoration processes in the amelioration of acidified soils.