1 Introduction
The sustainability of irrigated agriculture depends upon consistently achieving high irrigation application efficiency. High efficiency depends upon excellent design, as well as effective management. Much effort has been spent trying to improve irrigation management in NZ. Unfortunately, the design of many irrigation systems inhibits changes to management that would result in higher efficiency. A recent survey of irrigation operators reveals that this is often true of spray irrigators, as well as those using border-strip. Low irrigation efficiency threatens the renewal of water permits and thus the future of irrigated agriculture.
The aim of this report is to advance the sustainability of irrigated agriculture by providing information relevant tot he design of irrigation application systems that enable use of good irrigation management practices. It sets out to meet these aims by:
- Describing irrigation system performance measures relevant to irrigation design.
- Describing the key factors and critical decisions inherent in the design of irrigation application systems that have the potential to be operated effectively and efficiently.
- Illustrating the effects of some design decisions on performance measures.
- Assessing the feasibility of designing effective and efficient irrigation systems in New Zealand given current information and expertise.
There is an urgent and specific need to determine the maximum realistically achievable application efficiency for border-strip irrigation under typical Canterbury and Otago conditions. The most cost-effective means of doing so is to computer simulate the operation of border-strip systems under a wide range of conditions. Field data from a comprehensive set of field experiments was reviewed to determine its suitability for validating a computer model of border-strip irrigation. This review is included as Appendix I. The relevance of this specific area of work to the overall design process is that a properly validated model is the most cost-effective method of determining the effects on irrigation efficiency of the many border-strip design parameters. Without this tool it will be very difficult to design and compare surface and spray irrigation systems on the same basis.
The design of a travelling irrigator impacts on irrigation management in two main ways. The first is in the ability to easily adjust the mean application depth. The second is in the uniformity of the infiltrated depth of water. This latter aspect depends on interactions between application uniformity, application rate, the infiltration rate, and the micro-topography. A search was made of the international literature to establish what progress had been made since 1985 in understanding of the effects of the above interactions on the uniformity of the infiltrated depth of water and current abilities to predict infiltrated depth under field conditions. There is very little published work in this area. This is not surprising due to the substantial shift of research funds from irrigation (quantity) to water quality research that occurred in the mid 1980s, particularly in the United States. Accordingly, the topic of the planned review is identified in this report as a research issue.
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