Effects of biochar application and irrigation system on gregate and soil respiration

Biochar application enhances soil structural health and reduces carbon release by promoting aggregate stability and inhibiting microbial activity, while irrigation management exerts either stimulatory or inhibitory effects on soil aggregates and soil respiration (Rs) through water regulation. However, both are influenced by factors such as biochar properties, application rates, and irrigation regimes, leading to uncertainties in existing research findings. Based on data collected from 52 relevant studies, this research employed meta-analysis to quantitatively evaluate the effects of biochar and irrigation on the mean weight diameter (MWD), geometric mean diameter (GMD), and Rs of soil aggregates. Subgroup analysis, correlation analysis, and polynomial fitting were used to identify key regulatory factors. The results showed that biochar application significantly increased MWD and GMD, with the most pronounced effects observed for woody/herbaceous feedstocks, pyrolysis at medium-high temperatures (450–550 °C and > 550 °C), pH 8–9, application rates of 20–30 t·ha⁻¹ , and high carbon-to-nitrogen ratios (C:N > 150). Biochar exhibited a weak overall inhibitory effect on Rs (LnRR = −0.048, p < 0.05), but this effect was reversed under high-temperature pyrolysis (> 550 °C) and high application rates (> 50 t·ha⁻¹). In contrast, irrigation under high water volumes (> 1000 mm) and methods such as flood and sprinkler irrigation significantly reduced MWD and GMD but markedly stimulated Rs (LnRR = 0.528–0.853, p < 0.01). Subgroup analysis revealed that climate, soil texture, soil depth, and experimental duration significantly modulated these responses, with subtropical climates, clay loam soils, and surface soils (0–20 cm) showing the most pronounced effects. Correlation analysis further indicated that aggregate stability under biochar treatment was positively correlated with initial soil organic carbon, total nitrogen, and bulk density, whereas Rs under irrigation was primarily driven by soil pH. This study demonstrates that biochar has clear potential for improving soil structural stability and promoting carbon sequestration, while irrigation management requires balancing aggregate structure maintenance with microbial activity stimulation, providing a theoretical basis for sustainable agricultural soil management.