Effects of planting alfalfa on soil water-salt transport characteristics, physical properties, and organic matter turnover in coastal saline-alkali soils

Alfalfa (Medicago sativa) is widely cultivated in saline-alkali areas and demonstrates significant potential for soil improvement. However, systematic research on its amelioration effects on saline-alkali soils remains limited. This study was conducted at the coastal saline-alkali experimental base in Huanghua, Hebei, using an in situ field experiment to investigate the dynamic changes in soil volumetric water content, temperature, electrical conductivity (EC), bulk density, porosity, aggregates, saturated hydraulic conductivity (Ks), and organic matter (SOM) in alfalfa grassland (ALF) and saline-alkali wasteland (CK). The results showed that ALF treatment reduced soil volumetric water content in the 0–20 cm layer during spring and decreased soil temperature in the same layer during autumn. During the growing season, soil EC was significantly lower in both the 0–100 cm alfalfa root zone and 0–20 cm surface soil. ALF treatment suppressed surface soil salinization in spring and promoted leaching of salts during the rainy season. Specifically, in April and September, the EC in the 0–20 cm soil layer decreased by 85.10% and 90.91%, respectively, accompanied by reductions of 94.33% and 87.28% in the Na+ content and 86.94% and 92.07% in the Cl‒ content. The ALF treatment also improved soil physical properties. In the 0–10 cm soil layer, total porosity, capillary porosity, and non-capillary porosity increased by 0.16-fold, 0.16-, and 0.15-fold, respectively. In the 10–20 cm layer, soil bulk density decreased by 8.44%, while total porosity, capillary porosity, and non-capillary porosity increased by 0.28-, 0.21-, and 1.55-fold (P​0.25 mm) in the 0–20 cm soil layer increased by 4.68-fold (P​