Soil moisture is defined as the ratio of water content in the soil in percentage of volume or weight. It is the measure of the amount of water in the vadose zone (unsaturated zone). Soil moisture is a key variable for understanding hydrological processes in the unsaturated zone. It plays an important role in weather and climate predictions from the regional to the global scale by controlling the exchange and partitioning of water and energy fluxes at the land surface. Agricultural and irrigation management practices, especially in semi-arid and arid regions, largely depend on timely and accurate characterization of temporal and spatial soil moisture dynamics in the root zone because of the impact of soil moisture on the production and health status of crops and salinization (Vereecken et al, 2008).