Effects of halophyte Suaeda salsa continuous cropping on physical and chemical properties of saline soil under drip irrigation in arid regions

Soil salinization causes the degradation of soil structure, which seriously affects the global agricultural production. Currently, planting halophytes to improve saline soil has been widely used. However, most of the experiments were short-term, and the effect of long-term continuous cropping of halophytes on soil is still uncertain. This study aimed to investigate the multi-year effect of continuous cropping of euhalophyte Suaeda salsa on soil physicochemical properties. The space-for-time substitution approach was used to compare changes in soil physicochemical indicators under 3-year, 5-year, and 7-year continuous cropping periods of Suaeda salsa under drip irrigation, with bareland(0-year) serving as the control. In the 0–20 cm soil layer, the soil moisture content increased from 10.76% to 11.72–14.92%; in the 0–40 cm soil layer, the average bulk density decreased from 1.61 g cm−3 to 1.45–1.46 g cm−3 (P < 0.05), the average total porosity increased from 40.54% to 45.63–46.82% (P < 0.05), the average content of soil water-stable macroaggregates rose from 2.38% to 3.07–7.42%, and the average clay particle content declined from 20.88% to 16.63–18.63%; in the 0–60 cm soil layer, the average total salt content decreased from 48.11 g kg−1 to 12.43–22.01 g kg−1, and the average soil organic matter(SOM) content decreased from 8.73 g kg−1 to 7.40–8.15 g kg−1; in the 0–100 cm soil layer, the average pH value increased from 7.33 to 7.38–7.75, and the average content of Ca2+, Mg2+, Na+, K+, SO42-, and Cl- all decreased, whereas the average HCO3- content increased from 0.16 g kg−1 to 0.25–0.29 g kg−1. After 7 years of continuous cropping, the mean weight diameter (MWD) of 0–40 cm soil layer increased by 19.01%, the sodium adsorption ratio (SAR) of 0–40 cm soil layer decreased by 53.57% (P < 0.05), and the soil hydro-chemical type of 0–100 cm soil layer changed from Cl--Na+·Ca2+ to Cl-·SO42--Na+·Ca2+. The salt accumulation in the aboveground part of Suaeda salsa accounted for only 1.85–4.36% of the annual desalination quantity in the 0–100 cm soil layer. The continuous cropping of Suaeda salsa improved the soil structure and promoted salt leaching, which was the main mechanism of soil salt reduction. The results showed continuous cropping of Suaeda salsa under drip irrigation in arid regions is an effective method to improve saline soil, providing a theoretical reference for long-term continuous cropping of halophytes to improve saline soil in arid regions.