Institute for Agricultural Engineering research team manager Felix Reinders points out that, in South Africa, an area of 16- million hectares is being cultivated and, of that, 1 600 000 ha is being irrigated. With effective water management and good subsurface drainage, he highlights that improved soil health conditions can be created for successful irrigation farming to assist with food security in the country.
“Studies and research over 40 years in South Africa on the techniques of flood-, mobile- and micro-irrigation have contributed to the knowledge base that currently guides agricultural irrigation methods. The amount of water that is abstracted from the source and can actually be used by the plant is called the beneficial water-use component and optimised irrigation water supply is aimed at maximising this component.”
The council’s newly developed framework, which promotes a “measure, assess, evaluate, improve” method, draws on a water balance approach to improve water efficiency in agricultural irrigation. Reinders explains that the water balance approach aims to identify and quantify the different ways in which water is used in a system.
In the case of an agricultural irrigation system, most irrigation areas consist of a dam or weir in a river from which water is drawn by farmers, either directly or in some cases through a canal. Once the water enters the farm, it may further be stored in farm dams or enter an on-farm water distribution system, before being applied to the crop with an irrigation system.
Some water is lost while being conveyed and filtered, or is lost through evaporation or wind drift. These losses are identified and quantified, resulting in the irrigation system’s efficiency being defined as the ratio between the net irrigation requirements – the total amount of water that should ideally be available to the crop as a result of a planned irrigation system – and the gross irrigation requirements, which is the amount of water actually supplied to the irrigation system, of which some is lost.
“Historically, however, the reporting of irrigation efficiencies has been accompanied by insufficient scrutiny of the causes of water losses. There is a widespread illusion that irrigation efficiency is fixed by the type of irrigation infrastructure used rather than to the way a particular system has been designed and managed. In the past, improving performance and efficiency was, thus, incorrectly, associated only with an upgrade in infrastructure.”
However, the council’s framework covers four levels of water management infrastructure – the water source, the bulk conveyance system, the irrigation scheme and the irrigation farm, and the relevant water management infrastructure. The framework can also be applied to reassess the system efficiency indicators typically used by irrigation designers when making provision for water losses in an irrigation system, providing a more thorough interrogation of those losses.
During the course of the council’s research, 75 irrigation systems were evaluated, leading to the development of a new set of system efficiency values for design purposes, which enable sources of water losses to be more accurately identified and investigated to ensure the system functions optimally and is being managed correctly.
“This new approach can assist managers and designers alike to improve water efficiency in agricultural irrigation and incorporates detailed investigations with the flexibility to be applied at any level to improve irrigation system performance. This is critical for irrigation farming in a water-scarce country like South Africa from both an environmental and economical perspective,” concludes Reinders.
