Original Articles

An analysis of the ET/Ep-curve and its application irrigation scheduling

Published in: South African Journal of Plant and Soil
Volume 1, issue 1, 1984, pages: 12–16
DOI: 10.1080/02571862.1984.10634102
Author(s): M.S. BurgersDepartment of Plant Production,, P.C. NelDepartment of Plant Production,


The well known sigmoidel ET/Ep -curve often quoted in the literature for a variety of crops, merely depicts a smoothed curve drawn through points representing the average ET/Ep ratio for each depletion cycle co-ordinated with the middle day of the cycle. In this form it is of little use for monitoring the water balance of a crop during periods shorter than a normal irrigation cycle. The seasonal curve can be broken down into a number of separate curves based on the actual ET/Ep ratios (fi) within each depletion cycle. From these fi-curves, hypothetical curves were derived from which cumulative soil moisture depletion up to a given day within an irrigation cycle can be deduced with ease. This approach provides a way in which the efficiency of rain precipitation can be estimated to a higher degree of accuracy so that the irrigation programme can be adjusted accordingly.

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