In-field evaluation of irrigation system performance within the sugarcane industry of the south-east Lowveld in Zimbabwe.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2007.

The near collapse of the Zimbabwean sugarcane industry in 1991/1992 was concluded to be as a result of critical water shortages. This, combined with the uncertainty in the availability of water and a climate characterised by recurring droughts, strongly motivated the sugarcane industry in the South-East Lowveld to strive for improvements in water management and led to the establishment of the Mobile Irrigation Performance Unit (MIPU) in April 2000. Following an extensive literature review, evaluation methods and performance parameters were determined for the different irrigation systems currently in use in the sugarcane industry within the Lowveld of Zimbabwe, in relation to international standards. The systems in use included furrow, centre pivot, hand-move sprinkler, static sprinkler and sub-surface drip. The study also resulted in the development of some novel evaluation tools, examples being a simple device to measure the inflow to irrigation furrows and a uniquely shaped nozzle, used to determine operating pressures within the sub-surface drip system. Factors that can affect a system's performance were investigated and a comparison of the different irrigation system's performance parameters was shown. The evaluation results obtained by the Lowveld MIPU were also compared to MIPU results obtained internationally and reported in the literature. The MIPU evaluations are considered to be of great benefit to the farmer because an extensive database of irrigation system performance has been collated, against which farmers can benchmark their systems in the future. It is also possible that the repetitive nature of certain management and design variables which may be detrimental to system performance under local conditions, can eventually be rendered obsolete, for example, incorrect assumptions in scheduling of irrigation. The evaluation data can also be used to help facilitate objective decisions regarding the selection of irrigation systems to suit particular environments. The research indicates that the sugarcane industry could derive major benefits in improved irrigation systems performance by ensuring that irrigation system operators have the required calibre of skills and sufficient training. The results reported here should benefit farmers and result in refinements to the crop production system rendering it more cost effective and efficient.