where Zrjq is the average depth of water (mm) added to root-zone storage in the quarter of the field receiving the least water. This indicator differs from ea (Eq. 5.115) by the fact that it allows consideration of the nonuniformity of water application when underirrigation is practiced. As for ea, the numerator cannot exceed the SWD. The e¡q is used for surface, sprinkler, and microirrigation.
Potential Efficiency of Low Quarter (PELQ). Measured as a percentage (%), is used for design and corresponds to the system performance under good management when the correct depth and timing are being used. PELQ is given by 
where Zlq,mad is the average low-quarter depth infiltrated (mm) when equal to the management-allowed deficit (MAD) and DMAD is the average depth of water applied (mm) when SWD = MAD (about MAD, see Section 5.1).
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