In order to study the variation characteristics of soil moisture under different land use types in the moderate slope sandy area of loess hilly region

time domain reflectometry (TDR) was used in three land use types

which were maize farmland

Caragana korshinskii forest land and alfalfa grassland

in Wuzhai County

Shanxi Province. The soil moisture of 0-100 cm soil layer was observed for three years

and the seasonal variation and vertical distribution of soil water content of different land use types were grasped. The results showed that the seasonal variation curves of soil moisture in the three kinds of lands all showed M type distribution. The seasonal variations of the three kinds of lands were similar

but the difference of soil water content reached an extremely significant level (P<0.01)

which showed as follow alfalfa grassland > C. korshinskii forest > maize farmland. The soil water content of maize farmland and C. korshinskii forest showed S distribution with the increasing of soil depth

while the variation trend of alfalfa grassland was completely opposite to the other two lands. There was a significant correlation between the soil water content of 0-20 cm soil layer and precipitation in maize farmland

and there was a significant correlation between the soil water content of 0-60 cm soil layer and precipitation in C. korshinskii forest and alfalfa grassland. The soil water content had obvious vertical distribution characteristics. In 0-100 cm soil layer

with the increasing of soil depth

the CV of maize farmland decreased gradually and then remained stable

however

the CV of C. korshinskii forest decreased continuously

the CV of alfalfa grassland fluctuated at first and then decreased obviously. The coefficient of variation of surface soil water content was higher than that of deep layer. In the range of 0-100 cm

the soil layer of maize farmland could be divided into rapid change layer and active layer from top to bottom

and the soil layers of C. korshinskii forest and alfalfa grassland could be divided into three layers

which were rapid change layer

active layer and sub-active layer. The results of this study showed that forest land and grassland were better than farmland in conserving soil moisture

and forest and grassland were suitable land use patterns in the moderate slope sandy area of loess hilly region. It provided a theoretical basis for the management of soil moisture and the rational development and utilization of soil and water resources in this area.