Deep Seepage Under Nonuniform Sprinkler Irrigation: I. Theory

This study analyzes factors affecting deep percolation. Harmonic analysis is used to derive the effect of nonuniform irrigation on deep percolation. The Christiansen uniformity coefficient (CUC) is described by a sinusoidal function. It is shown to be proportional to the relative amplitude, the ratio between the amplitude $\left(\delta I\right)$ and mean water application $\left(Ĩ\right)$ of a sinusoidal wave. The amplitude is subject to smoothing by plant root systems of various sizes. A distinction is made between effective uniformity and observed uniformity. The theoretical study provides an analytical tool with which to evaluate the hydrological significance of irrigation uniformity. Deep percolation was shown to be affected by several factors. First is the difference between $Ī$ and the crops' water consumption. The greater the difference, the greater the amount of deep percolation. Of secondary importance is CUC. For any given amount of water, the amount that percolates below the root zone increases as CUC decreases. Smoothing of water distribution within the soil profile reduces percolation. This effect is more pronounced for a short rather than long distance between nozzles.