Crop production and water-use. IV. Yield functions for sugarbeet

The water-use model (watyield) was used to estimate a number of variables which were then related to the actual yields recorded in long term sugarbeet experiments carried out at several sites in England over the last 30–40 years. Nine functions were developed which are based on yield/water-input, yield/crop evaporation and (the equivalent of) relative yield/relative crop evaporation relationships. In all cases, highly significant linear correlations were obtained but the levels of precision, and degree of site specificity, varied. For irrigation planning and water allocation, three approaches are recommended with increasing sophistication and, in general, precision. These are (1) relating yield increases to the estimated irrigation need; (2) relating actual yields to crop evaporation totals; and (3) determining actual yields for rainfed and irrigated crops from the calculated seasonal totals of the ‘effective’ solar radiation intercepted by the crop canopy. These values can be estimated with the model using standard weather and soil physical data appropriate to the locality and the crop.