Effect of Tamarix ramosissima biochar on infiltration characteristics of saline water in coastal saline soil

Biochar has great potential for improving saline soil quality owing to its high porosity and organic carbon content. However, biochar was prepared from a halophyte (Tamarix ramosissima), which has rarely been used to improve saline soil quality, for exploring the characteristics of saltwater infiltration in saline soil. In this study, a soil column simulation method was used to study the effects of T. ramosissima biochar addition (mass fractions of 0, 1.1%, and 3.3%) and saltwater with different salinities (0, 5, and 10 g·L⁻¹) on water infiltration characteristics and water and salt distribution in saline soil. The results showed the following. 1) With an increase in the biochar addition amount and salinity of saltwater, the migration time of the wet front decreased by 34.40%–85.85%, and the infiltration rate increased by 6.71%–87.30%; moreover, the effect of biochar addition on the water infiltration characteristics of saline soil was greater than that of saltwater. 2) The addition of biochar increased the water content of 0–10 cm soil by 1.29%–9.23%. 3) After water infiltration, the soil salt content at 0–40 cm depth decreased significantly compared with the initial soil salt content, and the salt content in saline soil increased with the increase in salinity of saline water; however, no significant difference was found. The salt content was highest at a depth of 50–60 cm, and it increased significantly with the increase in biochar addition amount and salinity of saltwater, which increased by 5.21%–35.11% compared with the control group without biochar after fresh water infiltration. In conclusion, under different salinity saltwater infiltration conditions, T. ramosissima biochar addition can accelerate soil salt leaching, and its leaching effect noticeably increasing with an increase in the amount of added biochar. In this study, the effect was observed at an optimal addition of 3.3% of biochar. And the results for rational application of biochar and saltwater resource utilization in coastal areas provide the necessary theoretical basis.