Distribution Functions to Represent Center-pivot Water Distribution

The manufacturers of center-pivot systems widely use the Christiansen Uniformity coefficient to compare the irrigation uniformities. This single coefficient compares systems but does not provide a functional relationship of the variation of applied depths. The analysis of deficit and excess irrigation amounts requires a distribution function. Field catch can tests of center-pivot systems are used to estimate distribution functions. The four distribution functions investigated were normal, lognormal, uniform, and specialized power. It is concluded that the normal function is the best of the four functions to characterize the distribution of center-pivot systems. The volume of water applied in deficit of and excess to crop requirements is estimated with the normal distribution function.