Spatial and temporal variability of surface soil moisture in the depression area of Karst hilly region

Spatial and temporal variability of surface soil moisture(0-15cm)and its distribution patterns were analyzed using geostatistics in a typical depression area of karst region in Northwestern Guangxi Province.The results showed that surface soil moisture was generally low,ranging from 15.0% to 27.5% during sampling periods and had weak to middle variability.The middle variability often accompanied with low soil moisture.The parameters of the semi-variance functions of surface soil moisture and its influencing factors had seasonal variations.The values of nugget,sill and range ranged from 0.01 to 2.74,from 2.04 to 7.52,and from 6.0 to 36.8,respectively during the sampling periods.The variations of nugget and sill values were generally contrary to that of mean soil moisture.The range values were also contrary to the mean soil moisture at the initial and middle time of sampling,but had the same trend at the latter stages of sampling.These results suggested that mean soil moisture had substantial influence on the spatial and temporal variability of surface soil moisture in this area and could be used for establishing proper soil sampling strategy combined with the research objective.After eliminating the trend of soil moisture variability,the patterns of surface soil moisture's distributing pattern were stripe and patch like.The surface soil moisture in the plot area had different distributions at both spatial and temporal scales.Further,the distribution patterns were profoundly varied in the dry and rainy seasons.These results indicated that,mean soil moisture,topography,micro-morphology(rock cluster)and human management were the main influencing factors on the spatial and temporal variability and distribution patterns of surface soil moisture in the special physiognomy of the karst depression area.