Rice cultivation can mitigate soil salinization and alkalization by modifying the macropore structure in saline–sodic paddy fields

Abstract

Rice cultivation is generally accepted as one of the most effective biological strategies for reclaiming saline–sodic soils and ensuring food security; however, the underlying mechanism remains unclear. Soil macropores play a critical role in complex physical coupling processes such as ion absorption and water/salt migration, which are closely associated with soil salinization and alkalization. This study sought to investigate the impact of rice cultivation duration on soil macropores, salinization, and alkalization. Intact soil columns (0–20 cm) sampled from saline–sodic paddy fields with different cultivation durations (1, 5, and 12 years) were scanned using industrial X-ray computed tomography (XCT). Soil pH, soil salt content (SSC), and sodium adsorption ratio (SAR) were measured. Compared with 1 year of cultivation, longer rice cultivation significantly increased macroporosity by 46.25 %–123.34 %, larger macropores (> 200 μm) by 76.58 %–215.20 %, and maximum diameter pores by 30.43 %–65.22 % (P < 0.05). Moreover, macropore morphology and network parameters significantly improved with increasing cultivation duration, while soil pH, SSC, and SAR showed significant decreasing trends. Among them, SSC decreased from 5.64 g kg⁻¹ (1 year of cultivation) to 3.03 g kg⁻¹ (12 years of cultivation) [P < 0.05]. Furthermore, the structural equation model (SEM) indicated that rice cultivation years indirectly affected saturated hydraulic conductivity (K_s) by directly affecting soil macropore parameters, which ultimately affected SAR. In addition to K_s, specific surface area (SA) and fractal dimension (FD) were key factors affecting SSC. This study provides new insight into the underlying mechanisms of salinization and alkalization in rice cultivation from a macropore-scale perspective.