Spatial variability of soil moisture at a regional scale in the Loess Plateau

Soil moisture (SM) is one of the key factors for plant growth and eco-environment reconstruction on the Loess Plateau of China. To ascertain the spatial variability of SM in deep soil layers at a regional scale, 234 sampling sites were located with a GPS receiver, and 12 198 soil samples were collected with a soil auger before the rainy season in 2008.The distribution and variation characteristics of SM were evaluated by using classic statistical and geostatistical methods. Results showed that (1) SM decreased gradually from southeast to northwest in the horizontal direction, while in vertical direction, SM decreased from 0 to 90 cm and then increased from 90 to 500 cm soil depth. (2) Land use had a significant impact on the amount and profile distribution of SM. (3) The coefficients of variation and nugget ratios of SM at different depths in 0-500 cm profile demonstrated a decreasing-increasing trend, and these indices showed a good consistency in expressing the variation of SM. Understanding this information is beneficial to the management/mediation of soil and water processes, and to the restoration of eco-environment on the Loess Plateau.