Evapotranspiration of a genric wheat crop is estimated using the FAO crop factor method, where the timing of crop germination (break of season) is estimated using a two part rule, such that germination is assumed to occur if there is 25mm of rainfall over three days after 25 April and before 5 June, or if there is 5mm of rainfall over three days after 5 June.

The FAO crop factor method assumes that post-germination, there are four stages of crop growth. On any day during the crop lifecycle, the crop coefficient for the crop's growth stage is multiplied by the potential evaporation to give an estimate of plant evapotranspiration. Coefficients have been selected to suit WA wheat cropping.

The ten generic soil types used to model plant available soil water were developed by Yvette Oliver.

References

Oliver, Y.M. and Roberston, M.J. (2008), Quantifying the benefits of accounting for yield potential in spatially and seasonally responsive nutrient management in a Mediterranean Climate.

Ritchie, J.T. (1972), Model for predicting evaporation from a row crop with incomplete cover.