Effect of precipitation on the distribution of soil water-stable aggregates in a natural grassland

The aim of this study was to investigate the influence of precipitation level on the characteristics of soil water-stable aggregates (WSA), fractal dimension (D), mean weight diameter (MWD), and geometric mean diameter (GMD) in steppe grasslands. More specifically, the study determined the effects of precipitation level (50%, 100%, and 150% rainfall) on soil particle size in the Yunwu Mountain of Guyuan City, Ningxia, China. 1) The proportion of > 3 mm WSA in the 0 –10 cm soil layer was greater under 100% rainfall than under either 50% or 150% rainfall (P < 0.05). However, rainfall had no significant effect on the size of particles in the 10 – 20 cm soil layer. The > 3 mm and < 0.25 mm WSA in the 20 – 30 cm soil layers under 100% rainfall were significantly different from those under 50% and 150% rainfall (P < 0.05). 2) In the 0 – 10 cm and 10 – 20 cm soil layers, the D, MWD, and GMD were lower under 100% rainfall than under 50% or 150% rainfall, and in the 20 – 30 cm soil layer, D, MWD, and GMD decreased with increasing rainfall. 3) The soil fractal dimension was positively correlated with > 3 mm WSA (r = 0.43, P < 0.01) and negatively correlated with < 0.25 mm WSA (r = 0.49, P < 0.01). These results indicate that the stability of > 3 mm and < 0.25 mm WSA was sensitive to rainfall and that changes in rainfall will elevate D, MWD, and GMD.