where P is the pressure at emitters, A P is the variation in pressure along the unit or system, x is the characteristic exponent of the emitter, representing the sensitivity to variations in pressure, Ec represents the emitter characteristics related to variations in discharge, mainly representing the sensitivity to clogging and to temperature, Cv is the coefficient of manufacturing variation for the emitter, and FI represents the filtering capabilities of the system.
As for sprinkler systems, the irrigator has little control over the uniformity performance of the system except for the standard of system maintenance. Variables P and A P are set when the hydraulic design is made. Variables x, Ec, and Cv are set when emitters are selected, and FI is established when the filtration station is designed.
When the design is performed carefully, uniformities lower than foreseen should not be expected. However, lower DUmay occur when emitters selected by the user do not have the quality expected or the system is not properly maintained. Filter maintenance, lateral flushing, and the periodic chemical treatment against clogging are required to maintain the design uniformity. Evaluations in California, reported by Pitts et al.  and Hanson et al. , confirm the importance of these issues and show that actual field DU values are usually between 65% and 80%.
As with surface and sprinkler irrigation systems, the application efficiency ea also is determined by the combination of design and management variables, as indicated in the following functional relationship:
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