Temporal Persistence of Spatial Patterns of Soil Water Content in the Tilled Layer Under a Corn Crop

The temporal persistence of the spatial pattern of soil water storage (0∼0.2 m) under a corn ( Zea mays L.) canopy during drying and recharge periods were examined using spatial coherency analysis and transfer function theory. The corn crop caused both drying and recharge to occur at very specific scales, equal to the crop row spacing. The calculated transfer function, or time varying spectrum showed the scale at which the change in the spatial pattern was occurring and quantified the increase or decrease in variance at that scale. The spatial pattern of the drying coefficients, a measure of the relative drying rate, also varied systematically with significantly higher drying rates in the row area developing as the growing season progressed. The increase in relative drying rate in the row area caused the spatial pattern of drying to change at a scale equal to the crop row spacing. The calculated transfer function of the drying coefficients over the growing season indicated a steady increase in variance at that same scale, while the variance at other scales did not change significantly. An equation is developed relating the transfer function of soil water content in space to the spectrum of the process causing the change in the spatial domain.