Irrigation uniformity related to horizontal extent of root zone

Summary Harmonic analysis is used to derive the component waves of a given water distribution map. These components are then subjected to smoothing by root systems of various sizes, to obtain the effective variances and uniformity coefficients for these root systems. This approach helps to explain, for instance, why the effective uniformity by trickle irrigation is high, while the detailed actual distribution is very nonuniform; why the actual uniformity of under-canopy sprinkling of orchards need not be very high; or why it is usually better to have the rows of field crops parallel to the shorter spacing of the sprinklers. It is observed that ordinary distribution maps contain little variance in the shorter wave-lengths, thus suggesting a reduction in the number of collectors necessary for pattern determination. Another conclusion based on the same observation is that when plants spacing is half the sprinkler's spacing, a spatial shift between the crop and the irrigation system may markedly affect the effective uniformity.