RESEARCH ADVANCES IN IRRIGATION METHODS FOR EFFICIENT WATER APPLICATION: SOUTH AFRICA - Management, Performance, and Applications of Micro Irrigation Systems - page 48

Institute for Agricultural Engineering, and the installed systems were evaluated in-
field. The performance of the coefficient of uniformity (CU), distribution uniformity
(DU) and the scheduling coefficient (SC) were determined. The importance of this
is that high CU values and DU values in-field have a direct influence on the potential
yield of the crop. In this research it was illustrated that layout, pressure variation,
droplet size and maintenance of sprinkler systems have a significant impact on the
irrigation system's performance.
4.6 MANAGEMENT OF SURFACE- AND SUBSURFACE-DRIP IRRIGATION
SYSTEMS
Drip irrigation is considered to be one of the most efficient irrigation systems avail-
able, but through a WRC-supported research project evidence was obtained from the
literature as well as from on-farm and in-field testing that even this system can be
inefficient, as a result of poor water quality, mismanagement and maintenance problems
[10]. Apart from the research on the performance of various types and ages of drip-
pers [7] and filters under different water quality and typical farming conditions [15],
guidelines were developed to make the correct dripper and filter choice. Through this
research excellent guidelines were provided for proper choice, maintenance schedules
and management of filters and drip-irrigation systems.
4.7 THE WATER-BALANCE APPROACH
In a recently completed WRC research project on irrigation efficiency [11], the se-
lected approach is that irrigation efficiency should be assessed by applying a water
balance to a specific situation, rather than by the calculation of various performance
indicators, based on once- off measurements of samples. The purpose of an irriga-
tion system is to apply the desired amount of water, at the correct application rate
and uniformly to the entire field, at the right time, with the least amount of nonben-
eficial water consumption (losses), and as economically as possible. When applying
water to crops, it should be considered both as a scarce and valuable resource and
an agricultural input to be used optimally. Not all the water that is abstracted from a
source for the purpose of irrigation reaches the intended destination (the root zone)
where the plant can make best use of it. The fraction of the water abstracted from the
source that is used by a planted crop is called the beneficial water-use component.
Optimized irrigation water supply is therefore aimed at maximizing this component
and implies that water must be delivered from the source to the field both efficiently
(with the least volume for production along the supply system) and effectively (at
the right time, in the right quantity and at the right quality). Optimizing water use
at farm level requires careful consideration of the implications of decisions made
during both development (planning and design), and management (operation and
maintenance), taking into account technical, economic and environmental issues.
Perry [9] presented a newly developed framework for irrigation effi ciency as ap-
proved by the ICID (Fig. 1). He describes in detail the history and subsequent confu-
sion surrounding the calculation and interpretation of so-called irrigation or water use
'effi ciency' indicators. The framework and proposed terminology are scientifi cally