Abstract:

Soil water characteristic curve is one of the important soil water movement parameters affected by soil texture, bulk density, structure, and temperature. Three types of soil were selected in this study and five initial bulk density treatments were set to explore the effect of initial bulk density on soil water characteristic curve and its corresponding water movement parameters. The soil water characteristic curve and its water movement parameters were obtained by van Genuchten model fitting, and the effect of initial bulk density on soil water characteristic curve and corresponding water movement parameters of different types was analyzed. The results showed that in the near-saturation stage (S < 100 kPa), the water characteristic curves of the three soils under the same soil water suction all showed a gradual increase in soil volumetric water content with the initial bulk density. In the high soil water suction section (S > 100 kPa), the water characteristic surface of black soil gradually increased with the initial bulk density, and the water characteristic surface of red soil decreased with the increase in initial bulk density from 1.3 cm³·cm^-3 to 1.4 cm³·cm^-3. The difference lies in a remarkably steep increase in the water characteristic surface of loess soil from 1.3 cm³·cm^-3 to 1.4 cm³·cm^-3. The van Genuchten model had a good fitting effect on the soil water characteristic curve (R² > 0.99), which was suitable for fitting the water characteristic curve of the three types of soil under different bulk densities. The water movement parameters α and θ_s of the three soils were significantly negatively correlated with the initial bulk density (P < 0.01), and the water movement parameters α were significantly different from the initial bulk density of the black soil (P < 0.05). The water movement parameter θ_r of red soil was also significantly negatively correlated with the initial bulk density (P < 0.01), demonstrating a 10% reduction. A significant positive correlation was also found between the initial bulk density of black soil and soil water movement parameter n (P < 0.01). The initial bulk density of red and loess soil was negatively correlated with soil water movement parameter n, but the relationship was insignificant (P > 0.01). The variation range of water movement parameter n of the three soils under different initial bulk density treatments is small, and the variation range remains at approximately 0.1. The results can provide a reference for the acquisition of soil water movement parameters and hydrological process simulation under different types of soil and initial bulk densities.

Key words: soil water characteristic curve, centrifuge, initial bulk density, water movement parameters