3.5 Soil water storage over the soil wetting process and growing season
Regression analysis showed that the P1 to P13 rainfall processes (R1-13) and the change in soil water storage along the 1-m profile (SWS0-1 m) had a highly positive linear correlation at the 0.05 significance level under all land-cover types (Fig. 5a). The regression model of planted forest exhibited the highest slope value, approaching 0.78, followed by grass, bare land, shrub, and crop sites (Fig. 5a). Similarly, planted forest had the largest increment in SWS0-1 m (217.0 mm) and the highest rainfall transformation rate (RTR), approximately 45% (Fig. 5b). The crop site showed the smallest SWS0-1 m (129.3 mm) and RTR (26.8%). Moreover, our results indicated that revegetation improved rainwater interception, which increased the SWS0-1m by approximately 67.7%, 6.1%, and 31.9% for planted forest, shrub, and abandoned grass, respectively, compared to cropland, which promoted soil water infiltration and soil water storage (Fig. 5b).
The SM dynamic and SWS variation over the growing season showed that the average soil water content (ASWC) first increased and then decreased with increasing soil depth (Fig. 6). The ASWC of the grass site (16%) was significantly higher than that of the other sites across the entire profile (p<0.05), followed by forest (11.6%), shrub (9.5%), bare land (9.4%), and crop (8.1%). Moreover, land cover changed the distribution of the ASWC along the 1-m profile over the growing season. For the bare land and crop sites, the lowest ASWC occurred at the 0-10 cm depth, while the highest occurred at the 10-30 cm depth. After planting forest/grass and shrub, the highest ASWC occurred at the 70 cm and 50 cm soil depths over the growing season (Fig. 6), which was beneficial to the deep SM sustainability and vegetation growth supply.
A significant difference between the change in soil water storage (SWStotal) among the five monitoring sites over the growing season was discovered (p<0.05). The forest site had the largest SWStotal relative to the initial condition, approaching 83.3 mm. This was followed by the crop, grass, and shrub, all with approximately 60 mm increments of SWStotal, which were not significantly different. The bare land had the minimum increment over the growing season, merely 46.5 mm (Fig. 6). The above results illustrated that land cover significantly changed the infiltration pattern and SWStotal. In Fig. 6, the average SWStotal variation in revegetation construction (forest, shrub, and grass), approximately 68.1 mm, was higher than that of crop and bare land in the 0-1 m soil profile (p<0.05). This is the crucial implication that vegetation construction and recovery contributed to water storage and conservation within the 1-m profile in the growing season.