Relationship between Surface Soil Moisture and Root Zone Soil Moisture in Henan Province

Soil moisture is an important parameter in the research fields of hydrology, meteorology and agriculture sciences. But it is difficult to indicate spatial variability of soil moisture content at large area by conventional methods. Henan province is the most important grain production base in China, in which the yields of wheat and maize account for 1/4 and 1/7 respectively. Other studies have shown that the soil root length of wheat in 0-50cm depth accounts for more than 50% of the total length, so the soil moisture at the depth of 0-50 cm can be used to reflect the soil moisture availability in crop root layers for live crop. The development of remote sensing technology makes real-time or near real-time dynamic monitoring of soil moisture content in large area possible. However, the soil moisture in only 0-20cm soil depth is relatively accurate. Based on the really measured soil moisture data from January 2006 to January 2008 in Henan province, the paper analyses the relationship between surface soil moisture and root zone soil moisture, and considers the influences of season, soil texture. Then models using surface soil moisture to forecast root zone soil moisture are found. It is concluded that 0-50cm root zone soil moisture have a significant linear correlation with 0-10cm, 0-20cm and 0-30cm soil moisture and the deeper the depth of soil the better the coefficient of determination(R-2). Among four seasons, the relationship between surface soil moisture and root zone soil moisture in spring is the best, then in summer and winter, autumn in last. From textural point of view, because of the bad water retention capacity, water infiltration process of sandy soil is the fastest and instantaneous rainfall or irrigation process has only a shorter effect, so relationship between surface and root layer soil moisture of sandy soil is the best, loam soil is the second and clay soil is the worst. In the future, combined the results with models of soil moisture retrieved from remote sensing data, the real-time or near real-time dynamic monitoring crop root zone soil moisture from regional scale will be realized.