Faculty of Natural and Agricultural Sciences
School of Agricultural and Food Sciences
Department of Plant Production and Soil Science
Selected Highlights from Research Findings
Rainfall in semi-arid areas is usually erratic and insufficient to meet crop water requirements, resulting in yield fluctuations and food insecurity. Rainwater harvesting, which involves the collection and concentration of run-off for production purposes, can be implemented to mitigate the effects of seasonal droughts. Field trials were conducted at the Hatfield Experimental Farm during the 2007/08 season to study rainfall run-off relationships on run-off plots of different designs, and to improve the soil water balance (SWB) model as a tool for designing optimal rainwater harvesting management strategies for a particular region. Eight rainwater harvesting treatments were compared, using maize as a test crop. Conventional tillage was compared to tied ridges and six other in-field rainwater harvesting treatment combinations of different designs (run-off to cropping area ratios) and soil covers. Infield rainwater harvesting requires a balance between the cropped area and non-cropped (run-off) area. The run-off area contributes water to the cropping area, but cannot produce any yield itself. The larger the runoff area, the more water is transferred to the cropped area. However, too large a run-off area can be wasteful, as excess run-off water will be lost through deep percolation, which does not contribute to production. The researcher found that one design cannot work equally well under all climate and soil conditions and designs need to be optimised for different conditions. The results from one season, which may be unusually wet or dry, may give misleading results. It is, therefore, useful to develop a model that can be used to predict crop response over a longer period with historical weather data. All rainwater harvesting treatments in this trial improved maize growth and grain yields. Run-off estimation procedures were successfully incorporated into the SWB model to facilitate crop yield prediction under different rainwater harvesting scenarios. Long-term model simulations for Pretoria and Chokwe (Mozambique) revealed that smaller run-off areas are the best strategy in wetter areas or seasons, while larger run-off areas are best in drier conditions. This tool will be very useful to select best rainwater harvesting design strategies for different conditions to reduce yield fluctuations and food insecurity in semi-arid areas
Contact person: Dr JM Steyn.
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