Several parameters are used as indicators of the uniformity of water application to a field. The most commonly used [5] are described below.

Distribution Uniformity (DU). Calculated as a percentage (%), DU is defined by the ratio

where Zlq is the average infiltrated depth (mm) in the quarter of the field receiving the least water and Zav is the average infiltrated depth (mm) in the entire field.

The infiltrated depths may be replaced by the application depths in sprinkler irrigation (assumes no surface runoff or redistribution), and by the emitter discharges in microirrigation. Some authors prefer to replace the low-quarter averages in the numerator with the minimum observed values. This indicator then becomes the absolute distribution uniformity (DUabs).

Coefficient of Uniformity (CU). Calculated as a percentage (%) and also known as the Christianson uniformity coefficient, CU is defined as

where X are the absolute deviations of application (or infiltrated) depths from the mean (mm), X is the mean of observed depths (mm), and n is the number of observations. This indicator often is used in sprinkler irrigation.

Both DU and CU are related. The approximate relationship between them is [11]

The parameter CU relates to the standard deviation (sd) and the mean (X) of the individual observations by

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