CROP PRODUCTION AND WATER-USE .1. A MODEL FOR ESTIMATING CROP WATER-USE WITH LIMITED DATA

An attempt was made to re-assess the results of irrigation experiments carried out in the UK during the last 30-40 years in order to develop functional relationships between crop yield and actual water-use. It was first necessary to develop a model, based on relatively simple functions, which could be used to predict actual water-use (evaporation and transpiration). The derivation of this model, known as WATYIELD, is reported here, whilst its application and validation for sugarbeet and for potatoes are described in subsequent papers. Simple functions relate components of evaporation to the proportion of the incoming solar radiation intercepted by the crop canopy, reference crop evapotranspiration, the precipitation and irrigation amounts and the soil water deficit. Transpiration is also related to soil hydraulic characteristics, rooting density and potential evaporation rate.