Results from the evaluation of floppy sprinkler systems and SSD systems in the south east lowveld of Zimbabwe are also discussed. In this paper, rationale and procedures for the evaluation of the pumping plant, overhead sprinkler, sub-surface drip (SSD), centre-pivot and furrow are summarised. The information from an evaluation should help a grower reduce input costs, increase returns and, if necessary, provide motivation for a designer to implement remedial measures if a design is not up to standard. The objectives of evaluating the performance of an irrigation system are listed below: l to determine if the system is working according to grower assumptions/design specifications in terms of the amount of water applied, and to thereby provide a basis for improved irrigation scheduling, l to determine how much variation there is in the amounts of water applied and whether or not the measured variation will have a significant impact on crop yields, deep percolation (drainage) and runoff losses, fertiliser use efficiencies and production costs, l to determine the causes of the variation in applied water and investigate and recommend cost effective remedial action, l to assess whether or not the conveyance system is sized within design norms that are based on a fair balance between capital and operating costs, l to check the efficiency with which power is being used, l to produce recommendations to improve on any aspects that will lead to more effective use of water and energy. An irrigation system evaluation involves taking in-field measurements and then using scientific and engineering principles to assess these measurements in the light of performance standards. This information is extremely important if improvements are to be made to irrigation management practice and/or design, and to facilitate objective selection of appropriate irrigation systems. This unit, together with ZIMsched (Lecler, 2000) can provide information/data to quantify and explain these performance differences. It is with this in mind that the sugarcane industry in Zimbabwe has established a Mobile Irrigation Performance Unit (MIPU). Reasons for differences in performance could be a combination of environmental conditions, scheduling, system performance/ design and management. Also, the fact that one grower can achieve higher sugarcane yield per unit of water used compared to another, in the same area, needs investigation.
The typical as opposed to the potential performance of these systems and the respective management criteria, under local conditions, can be major factors in the choice of one system over the other. Keywords: irrigation, system, evaluation, performance, sugarcane, Zimbabwe Introduction In the present irrigation market there are a variety of irrigation systems accessible to the grower. Growers will have a benchmark to measure their systems against in the future, and the repetitive nature of certain management and design variables which may be detrimental to system performance, may eventually be rendered obsolete. When all the different types of irrigation systems have been evaluated in the area, an invaluable database would have been collected. The SSD distribution (DU) values range from 33-94%, with the statistical (SU) values ranging from 53-98%. The floppy sprinkler coefficient of uniformities (CU) range from 66-84% with the distribution uniformities (DU) ranging from 59-78%. Results from in-field distribution evaluations of seven floppy sprinkler and 27 SSD systems are tabulated. Rationale and summarised procedures for the evaluation of pumping plants, overhead sprinklers, sub-surface drip (SSD), centre pivot and furrow irrigation systems are presented.
The impact that the application of a system can have on crop yield and irrigation efficiency, is further motivation to undertake system evaluations. This information can also help with the selection of one system over another given local constraints. 1 IRRIGATION SYSTEM EVALUATION BAK GRIFFITHS AND NL LECLER Zimbabwe Sugar Association Experiment Station Private Bag 7006, Chiredzi, Zimbabwe Abstract Evaluation of irrigation system performance facilitates objective analysis of the typical as opposed to the potential performance of various types of irrigation systems and the respective management criteria, appropriate for local conditions.