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Wageningen University (2012)

An assessment of the economic water use efficiency and productivity of the upstream and downstream catchments’ agricultural production, South Africa : a case study of the Baviaanskloof and Gamtoos Valley, Eastern Cape, South Africa

Ndeketeya, A.

Titre : An assessment of the economic water use efficiency and productivity of the upstream and downstream catchments’ agricultural production, South Africa : a case study of the Baviaanskloof and Gamtoos Valley, Eastern Cape, South Africa

Auteur : Ndeketeya, A.

Université de soutenance : Wageningen University

Grade : Master of Science (MS) 2012

Résumé
Water scarcity is a problem that is threatening the world and pressure is growing for the agricultural sector to cut its water use. This has given rise to the interest in water use and efficiency in water management studies. With the aim of assessing the productivity of Baviaanskloof valley after serious land degradation, a study was carried out to determine the economic and physical water use efficiency for the year 2010 and the results were compared to the downstream catchment, the Gamtoos Valley. Water productivity for the year 2011 was also calculated for the Baviaanskloof using actual crop water use from Cropwat simulation. Data was collected from November 2011 up to February 2012. Interview with farmers and personnel from the Gamtoos Irrigation Board (GIB) were done to get information on water use, crops cultivated, yields, prices, costs and cropping seasons. In some cases the bucket method was used to validate the figures on water use obtained from the farmers. Using irrigation data on use from farmers and other soil, crop and weather parameters from the Agricultural Research Council the Cropwat model was run to simulate the actual crop water use and to determine the amount of over/under irrigation. All the raw data was then analyzed using the formulas’ : eWUE= net income/total water use, WUE=yield/total water use, WP=Yield/ actual water use. Comparisons were made per catchment from plot level to farm level then at basin level. Some differences were noticed among farmers and the reasons varied from yield, water use and net income. Major differences were noticed between the two catchments. The eWUE was 1.99 and 6.81R/m3 for Baviaanskloof and Gamtoos respectively. For the common crops maize and potatoes the eWUE was higher again for Gamtoos than for Baviaanskloof : for potatoes it was mainly because of low yields (10t/ha) compared to 35t/ha from Gamtoos whilst in maize it was due to high water use of about 1200mm used by the Baviaanskloof farmers whereas the other farmers used only 420mm. The water productivity was higher than the WUE for the Baviaanskloof for most crops. The range between WP and WUE was huge for maize, potato, wheat and tobacco whilst it was slight for the seed vegetables. This shows there is a lot of room for improvement. From the results the recommendation is for farmers to focus more on high value crops. The results also showed that the total amount of water currently used for crop production is enough to irrigate approximately 271 hectares of citrus hence it is feasible for farmers to change to citrus production from a water availability standpoint. However, strong organisation and linkages especially with downstream farmers and GIB are needed to improve the agricultural practices in the upstream area. Further exploration still needs to be done to see what other land use options can be adopted in the area and the costs and benefits.

Mots clés : water use efficiency / agricultural production / irrigation / water management / south africa

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