Spatial and Temporal Distribution of Soil Water in the Tilled Layer Under a Corn Crop

Abstract Measurements of the spatial distribution of the surface layer (0–0.2 m) soil‐water content under a corn crop, ( Zea mays L.) throughout the growing season were obtained on a Typic Hapludalf (London silty clay loam) soil near Guelph, Ontario, Canada. One hundred surface soil water content measurements were taken nondestructively every 1 to 2 d in a 20‐m long transect using permanently placed time domain reflectometry (TDR) transmission line probes. The sampling interval was set so that between every two rows of corn in the transect, a TDR probe was situated in each row, directly between the rows (interrow) and halfway between each row and interrow position. Systematic spatial differences in surface soil water content were observed throughout the growing season with the interrow position almost always greater than the row position. Significantly lower bulk density in the row compared to the interrow accounted for differences early in the growing season. Significantly higher drying rates in the row caused greater differences at later crop growth stages. Soil water recharge from rainfall was also greater in the row compared to interrow, which was attributed to interception and subsequent stemflow. The preferential drying and recharge in the row area caused the spatial variability to be time dependent and the temporal variability to be space dependent.