Variation of soil organic carbon and bulk density during afforestation regulates soil hydraulic properties

Grain to Green program on arable land has been conducted for decades in semi-arid regions of North China. However, it remains uncertain how afforestation practices affect soil hydraulic properties (SHP). Two afforestation types, i.e. shrubland (SL) and woodland (WL), and the adjacent cropland (CL) were investigated to determine afforestation effects on SHP in this area. Disturbed and undisturbed soil cores were collected in three experimental sites. Soil field capacity (FC), wilting point (WP), and available water capacity (AWC) increased in SL compared to the CL. Soil saturated water content, however, decreased significantly in both SL and WL. Correlation and redundancy analysis identified that bulk density (BD) and soil organic carbon (SOC) were the main factors regulating SHP across different land uses. Lower saturated water contents in afforestation sites were likely driven by the higher BD, compared to the adjacent cropland. FC, WP, and AWC were positively correlated to SOC content. While afforestation may not increase the saturated water content of a landscape, our results indicate that it can improve soil water retention and could be an effective practice for soil and water conservation.