Soil acidification poses a significant challenge to soil health worldwide, and biochar emerges as a promising remedy. Nonetheless, a comprehensive evaluation of the impact of biochar on soil pH change is lacking, leaving considerable uncertainty regarding its efficacy across different environmental and management contexts. Here, we conducted a meta-analysis of 232 global studies to elucidate the impact of biochar on soil pH and identify key variables influencing its effectiveness. Our findings revealed that biochar application significantly increased soil pH by an average of 5.59%, but it decreased soil pH under certain circumstances. The raw material and pyrolysis temperature of biochar determine its pH. Furthermore, the biochar pH and initial soil pH modulate the magnitude of the biochar liming effect. High soil cation exchange capacity (CEC) values attenuate the biochar liming effect. When combined with organic nitrogen (N) fertilizer (6.95%), biochar increases soil pH more than when combined with inorganic N fertilizer (4.57%). Paddy fields exhibited a more pronounced response to biochar-induced pH elevation (5.98%) than dryland fields (3.75%), attributable to higher MAP, lower initial soil pH and soil CEC, higher biochar application rates and pH, and higher N fertilizer application. Overall, our meta-analysis underscores the lime-enhancing potential of biochar and the pivotal roles of MAP, biochar pH, initial soil pH, initial soil CEC, and farmland utilization mode in shaping its effectiveness. Graphical Abstract

In China, the ridge-furrow water conservation planting (RC) system is advantageous for improving crop yields and rainwater use efficiency. In RC planting system, plastic film-mulched ridges are employed for water harvesting while the furrows serve as infiltration and planting belts. To optimize the RC system and to overcome problems due to the lack of water in semi-humid areas at risk of drought, we mulched the furrows with 8% biodegradable film (RCSB), liquid film (RCSL), or no mulching in the furrows (RCSN), while conventional flat planting (CF) was employed as the control. After four year (2007-2010) consecutive field study, the results showed that the soil water storage level in the 0-100 cm layer with four treatments was ranked as follow: RCSB>RCSL>RCSN>CF, while the RCSB and RCSL were 26.3 and 12.2 mm greater than RCSN, respectively. Compared with CF, the average soil temperature was significantly (P<0.05) higher by 3.1, 1.7, and 1.5 ℃ under the RC planting treatments (RCSB, RCSL, and RCSN) during each year, respectively. The average ET rate of RC treatments were all lower than CF in each experimental year, and the average decreased by 8.0% (P<0.05). The average yields with RCSB, RCSL, and RCSN increased by 2665, 1444, and 1235 kg ha–1, respectively, and the water use efficiency (WUE) increased by 51.6%, 25.6%, and 21.1%, compared with CF. RCSB obtained the highest economic benefit, the average net income was higher than CF by 4020 Yuan ha–1. In conclusion, we found that RC planting with biodegradable film mulching in the furrows is the best cultivation pattern in the semi-humid areas of China in terms of both environmental and economic benefits.