High-pyrolysis-temperature acidified straw biochar improves soil hydrological functioning and increases maize yield in saline soils

Biochar contributes to the restoration of soil fertility and crop productivity in saline-affected farmlands. Soil hydrological functioning is a key indicator for assessing the degradation and rehabilitation of saline soils. However, the mechanisms by which acid-modified maize straw biochar produced at different pyrolysis temperatures regulates the hydrological properties of saline soils remain unclear. In this study, a four-year soil amendment experiment was conducted in moderately saline soils of the Hetao Irrigation District in China to evaluate the effects and underlying mechanisms of acidified biochar produced at three pyrolysis temperatures (C1: 300 °C, C2: 500 °C, and C3: 700 °C) and applied at two rates (T1: 10 Mg ha - ¹ and T2: 20 Mg ha - ¹) on soil hydrological properties. The results showed that: (1) application of acidified biochar significantly decreased soil salinity, pH, and bulk density, while increasing soil water content and organic matter. Moreover, it markedly enhanced crop yield and biomass; (2) acidified biochar markedly improved soil hydrological properties (0–40 cm), with the C3T1 treatment performing best, increasing soil saturated water-holding capacity, field capacity, soil water storage, and saturated hydraulic conductivity by 17.35%, 27.91%, 14.31%, and 26.92%, respectively; (3) Principal component analysis (PCA) and Mantel test results indicated that soil hydrological properties were positively correlated with crop yield, biomass, clay content, soil organic matter, and total porosity (p < 0.05), but negatively correlated with bulk density, electrical conductivity, and sand content (p < 0.05). Random forest analysis further highlighted that improvements in soil hydrological properties were primarily driven by changes in biomass, SOM, bulk density, clay content, and total porosity. Overall, this study demonstrates that acidified biochar produced at a high pyrolysis temperature (700 °C) and applied at 10 Mg ha - ¹ effectively enhances the physicochemical and hydrological properties of saline soils, thereby improving their productivity. These findings provide important guidance for developing biochar-based strategies to rehabilitate saline-affected agricultural soils.