Biochar enhances soil hydrological function by improving the pore structure of saline soil

The poor soil structure caused by salinization is a major factor affecting crop growth and soil structure will further affect hydrological function. Biochar is widely used to improve soil physical structure because of its special porous material. However, the mechanism of soil pore structure on hydrological function (e.g., soil saturated hydraulic conductivity, plant available water, least limiting water range) after biochar incorporation in saline soil remains unclear. Therefore, the present study examined the response of soil structural properties of different biochar addition in saline clay loam, and subsequently assessed how the pore structure influence soil hydrological function. The study involved four treatments: CK (Control)、C₁ (7.5 t ha⁻¹ biochar)、C₂ (15 t ha⁻¹ biochar)、C₃ (30 t ha⁻¹ biochar). Soil aggregate stability increased from 15 % to 30 % when the amount of biochar addition increased from 7.5 t ha⁻¹ to 30 t ha⁻¹. The highest connectivity index (2.36) and the highest fractal dimension (2.56) were found at the biochar addition of 30 t ha⁻¹. Biochar addition reduced the proportion of small pores (<50 µm pore size) at both soil depths of 0–10 cm and 10–20 cm, whereas increased the proportion of large pores (>300 µm pore size). Biochar amendment reduced the soil penetration resistance, with the soil saturated hydraulic conductivity, plant available water and the least limiting water range were measured 46 %, 27 % and 40 % greater in rate of 30 t ha⁻¹ biochar addition as compared with those of the CK, respectively. Pearson’s correlation analysis and redundancy analysis revealed that the soil saturated hydraulic conductivity was positively correlated with large pores (diameter >300 μm) and pore connectivity (p < 0.05). The lowest least limiting water range of the CK was primarily constrained by a relatively higher penetration resistance. The improved pore connectivity and elongated pore structures were the key responsible for the reduced penetration resistance in biochar-amended soil, which subsequently increased the least limiting water range. These quantitative estimates highlight the positive effects of biochar amendment-induced soil pore structure alternations towards improving soil hydrological functionalities. These findings are essential for devising effective strategies to enhance sustainable agriculture in saline soils.