Main Controls of Soil Moisture Dynamics in an Agricultural Landscape in Central Pennsylvania

Soil moisture is one of the key parameters governing the interactions between the atmosphere, land surface, and ground water. Factors controlling the spatial and temporal patterns of soil moisture include soil properties, topography, vegetation, radiation, and precipitation. Previous studies revealed that the importance of these factors varied in different fields due to the change of land use, climate, drainage, soil and geological conditions. This study investigated how soil moisture controlling factors change at different soil depths, in different landforms and seasons in a ridge and valley agricultural landscape in central Pennsylvania. Correlation analysis between soil moisture and different factors (including clay content, organic matter content, soil depth, and terrain indices) were conducted. Temporal stability of soil moisture in different crop fields was used to determine the effects of crop type on soil moisture distribution. During the non-growing season, the surface soil moisture (0-0.2 m) was correlated with both soil properties and terrain indices (p<0.05). However, soil properties' effect on subsurface soil moisture (0.3-0.5 m and 0.7-0.9 m) was not significant due to higher water content of the subsurface soil and the spatial homogeneity of subsurface soil properties, and therefore the main controlling factor was topography. The correlation between both surface and subsurface soil moisture and terrain indices was greater in sloping areas (slope>8%) than in flat areas. During the growing season, crop types (corn and soybean) were the main controlling factor of surface soil moisture due to plant uptake dynamics. Soil properties were also important in controlling surface soil moisture, but the effect of topography was limited. In the subsurface, crop type effect on soil moisture disappeared since the observed root penetration depth was largely <0.4 m. Topography was the main controlling factor for subsurface soil moisture during the growing season.