Abstract: To understand the distribution characteristics and influencing factors of soil bulk density across different soil layers in the loess region, we measured soil bulk density at 0-20, 20-40, 40-60, 60-80, and 80-100 cm layers in 98 locations in Caijiachuan watershed in the loess region of western Shanxi. We analyzed the distribution characteristics, the main influencing factors of each soil layer and their contribution rates to soil bulk density by using classical statistics and geostatistics methods. The results showed that: (1) Soil bulk density ranged from 0.79-1.78 g·cm^-3, and increased with increasing soil depth in the 0-100 cm depth. The variation of soil bulk density decreased with increasing soil depth. (2) Gaussian model was the best fitting model for soil bulk density at 0-40 cm layer, while exponential model was the best fitting model at 40-100 cm layer. The spatial dependence of soil bulk density decreased with increasing soil depth, showing strong, moderate and weak spatial dependence at 0-20, 20-60 and 60-100 cm layers, respectively. (3) Soil bulk density at 0-40 cm layer was mainly affected by vegetation and soil factors, while that at 40-100 cm soil layer was mainly affected by elevation and soil factors, suggesting that the effects of vegetation restoration on soil bulk density were mainly concentrated in the surface layer. Our results provide important reference for in-depth understanding of regional soil bulk density distribution under the vegetation restoration and scientific assessment of regional ecological benefits and ecological services of vegetation restoration.

Key words: soil bulk density, soil layer, vegetation restoration, loess region