Thursday, November 8, 2007 - 10:45 AM
331-9

The Soil Water Balance (SWB) Model: A Decade of Development, Refinement and Application in South Africa.

John Annandale1, Joachim M Steyn1, Nebo Jovanovic2, and Nico Benade3. (1) University of Pretoria, University of Pretoria, Department of Plant Production, Hatfield, 0002, SOUTH AFRICA, (2) University of the Western Cape, Dept of Earth Sciences, Belville, 7535, South Africa, (3) NB Systems, PO Box 15102, Sinoville, 0129, South Africa

In 1993, Prof Gaylon Campbell from Washington State University, introduced us to a simple but mechanistic, generic crop growth water balance model called NEWSWB. Our research at the time on water requirements of vegetables under well watered and water stress conditions, provided the data to convince us that the model was a valuable tool, capable of simulating the water balance with sufficient accuracy for irrigation scheduling purposes. This led us into a development phase, in which the focus was on determining crop parameters for a wide range of crops, and on developing a user-friendly interface for the model, that we called SWB. More technical developments have included the incorporation of a chemical equilibrium module to predict gypsum precipitation when irrigating with gypsiferous mine water, and the development of an above and below surface 2D version of SWB, for micro irrigation management of hedgerow orchards. The model has been very useful for research, teaching and consulting, but widespread on-farm use for irrigation management, despite several technology transfer actions, remains a challenge. Our focus now is on using SWB to develop site specific irrigation calendars that should be simpler to use, but should still help farmers become more quantitative about irrigation.

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