Agri Kultuur March/ Maart 2016 - Page 14

I Felix Reinders ARC-Institute for Agricultural Engineering t is imperative that an irrigation system must be designed correctly and managed properly to optimise yields. Irrigation implies that water is applied artificially to supply in the crop’s needs and irrigation water managers from farm level to scheme level, as well as designers of irrigation systems use a planning tool for water requirement estimates to enable them to supply the right amount of water at the right time to a crop. This tool is called SAPWAT (short for South African procedure for water requirements) and was developed in South Africa. good planning and management of ning. irrigation water is of utter imThe weather data included monthly portance to increase the efficiency of data and have up to fifty years of irrigation water use. daily data in 5100 weather station This user-friendly computer model data sets with an amount of more has been developed that enables than 38 million records. This allows irrigation water users to plan the SAPWAT3 to be used internationally. amount of irrigation water required Daily data for any number of succesby irrigation farm, an irrigation sive years is used to do year-on-year scheme or a water management area irrigation requirement estimates, the on a month by month basis. SAPresult of which allows the user to WAT, was first published and used in include risk analysis as part of the 1999. It was a further development planning process. of CROPWAT and is used by more It furthermore include 2500 crop than 300 users in 13 countries, even records by providing for differences though it was designed against the in growth and development because background of South African needs. of planting different cultivar types at Good planning of irrigation water SAPWAT was continuously improved different times of the year and in requirements for the irrigation indus- and upgraded, with the newest verdifferent climates. Irrigation stratetry advance the overall management sion published as SAPWAT3. SAPgies can be varied to demonstrate of water and its distribution beWAT3 is based on the Food and Agthe effect of different strategies on tween human, industrial, irrigation ricultural Organisation’s Irrigation irrigation requirement. This allows and environmental requirements. In and Drainage Paper no 56, “Crop the user to devise irrigation strateSouth Africa, where a number of the Evapotranspiration”, which reflects gies that will aim at maximizing rainmajor rivers are already overthe international thinking on the fall use efficiency and thus reduce extended, and where irrigation uses standardization of approaches to irrigation water requirements. about 60% of the total water supply, irrigation water requirement planSAPWAT3 (see figure 1) is designed for maximum user interaction with an approach which contributes to the user’s understanding of issues affecting good irrigation water planning and management. It is not a crop growth model but it is designed to allow the user to imitate through interaction the situation in an irrigated field. This allows the user to do “what if” with different irrigation scenarios to see what the effect of a specific management decision is on irrigation water requirement. Figure 1: SAPWAT software