Quantifying Performance

Irrigation performance often is described in terms of the water application efficiency and water distribution uniformity. Because there are many aspects to irrigation and several irrigation methods, a wide range of performance parameters have been proposed but there is no consensus for standardization. Next some basic performance parameters that have been widely used are discussed.

Efficiency

The definition of water application efficiency is not well established despite the fact it is used worldwide. Reviews of various efficiency terms are provided elsewhere [5-7].

The classical definition of irrigation efficiency introduced by Israelsen in 1932 is the ratio between the irrigation water consumed by the crops of an irrigated farm or project during crop growth and the water diverted from a river, groundwater, or other source into farms or project canals [8]. However, this definition is the cause of much misinterpretation [8]. It is necessary to make a clear distinction between water consumption—which includes evaporation, transpiration, and water embodiment in a product—and water use, which also includes nonconsumptive components that may be of practical necessity (such as leaching salts) and may be available for reuse. Irrigation performance evaluation depends on the point of view.

The term "efficiency" is restricted to output/input ratios of the same nature, such as the ratio of delivered/diverted water volumes or infiltrated/applied water depths. In both cases it is possible to identify the nonconsumed fraction that can be recovered or reused for agriculture or other purposes. Water-use efficiency (WUE) should be used to represent plant or crop output per unit water use (i.e., the photosynthetic WUE, the biomass WUE, or the yield WUE, as proposed by Steduto [9]). This concept is not used as a measure of irrigation performance.

The efficiency terms used in on-farm irrigation to measure the performance of water application are the following:

Application Efficiency ea. Measured as percentage (%), this is defined as ea = 100( Zr / D), (5.115)

where Zr is the average depth of water (mm) added to the root zone storage, and D is the average depth of water (mm) applied to the field. The condition

must be met everywhere on the field; SWD is the soil water deficit (mm), at time of irrigation.

Application Efficiency of Low Quarter (e¡q). Measured as a percentage (%), e¡q is defined by Merriam and Keller [10] as

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