Soil moisture variability on the landscape as a function of land use: implication for remote sensing of surface soil moisture

Knowledge of the spatial and temporal distribution of soil moisture under a variety of landscapes and soil conditions is essential for the proper management and utilization of available water. The spatial distribution of soil moisture in the field is often related to the heterogeneity of soil hydraulic and other physical properties. During the Southern Great Plains Hydrology Experiment (1997) in Oklahoma, time domain reflectometry (TDR) measurements were made on a full-section wheat field, open rangeland, and a field dominated with sodic soils along 7 transects spaced at 100 meters. The spacing between sampling points along the transects was also 100 m. Six rainfall events occurred during the 24-day measurement period. Soil moisture content ranged from 0.3 to 0.70 cm/sup 3//cm/sup 3/ in the field during the experiment. Time series analysis showed no significant difference in surface soil moisture between the rangeland and harvested wheat fields. They were consistently drier than the sandy, bare sodic soils. The standard deviation decreased with decreasing soil moisture in the sodic soils and cut wheat fields. The coefficient of variation decreased with increasing soil water content. Results of this study will aid in the development of hydrological and land surface models.