ISHS Acta Horticulturae 792: V International Symposium on Irrigation of Horticultural Crops
USING ETo TO DETERMINE WATER ALLOCATIONS |
| Author: | M.A. Skewes |
| Keywords: | crop evapotranspiration, volumetric, crop coefficient, crop calendar, water use, net irrigation requirement |
| Abstract:
In response to The State Water Plan - South Australia (Department for Water Resources, 2000), and in order to facilitate better resource management, current area based water allocations across South Australia are being converted to volumetric allocations. In other areas of the state, previously unregulated water resources are being prescribed, and volumetric water allocations are being issued to current and prospective users. The methodology of Allen et al. (1998) was used to determine reference evapotranspiration (ETo) in the various areas where water is being allocated, and crop evapotranspiration (ETc) of the crops being grown in those areas. ETo was determined from a standardised set of long-term evaporation data. Community consultation was used as a platform for collecting information about crop types grown in the area, and the typical calendar of events for those crops. This information was key to constructing crop coefficient curves, which were used to determine ETo for each crop from ETo for an area. Variation in crop calendars for a single crop, especially when considering vegetable crops, led to the splitting of some crops into different growing seasons, with different allocations. Also, the crop coefficients given by Allen et al. (1998) represent maximum crop evapotranspiration. Some crops, such as winegrapes, are not always managed for maximum evapotranspiration, and alternative coefficients were sourced for these crops. There are other crops for which Allen et al. (1998) do not provide coefficients at all, and these were also sourced elsewhere. Comparison of calculated irrigation requirements with pumped volumes indicated that some irrigators were applying well in excess of calculated figures, whilst others were applying much less. Reasons for this are explored, and the major issues associated with using ETo as a basis for water allocations are discussed. | |
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