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/Epratio 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/Epratios (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.S. Afr. J. Plant Soil1984, 1: 12–16