Agriculture Reference
In-Depth Information
to improve water management practices in order to achieve an increase in overall
efficiency. In general, evaluation helps to identify problems and the measures
required to correct them. No single indicator is satisfactory for all descriptive pur-
poses. In general, a set of indices are used for evaluating the performance of an
irrigation scheme. Most commonly used indices are described in this chapter. In
addition, evaluation procedures for specific irrigation systems (e.g., furrow, border,
sprinkler) are described in details.
4.1 Irrigation Efficiencies
In order to determine how much irrigation water to apply, you need to estimate
the efficiency of the irrigation system. There are many ways of thinking about,
determining, and describing concepts relating to irrigation efficiency. Simply speak-
ing, the “efficiency” implies a ratio of something “in” to something “out”. Many
efficiency terms related to irrigation efficiency are in use or have been proposed.
Efficiency can be measured at the scale of a whole catchment, at the individual
plant scale, and at almost any level in between. The scale of measurement is of crit-
ical importance in tackling the issue of improving efficiency and must be matched
with the specific objective. For example, when measuring on-farm efficiency, too
broad a scale makes it difficult to determine what the causes of low efficiency are
and what can be done to improve the situation. Going to a smaller scale excludes the
consideration of wider issues, such as delivery system losses and inefficiencies but
is necessary to clearly identify real opportunities for improvement at the individual
property/manager scale. Commonly used irrigation efficiencies are described below.
4.1.1 Application Efficiency
Water application efficiency expresses the percentage of irrigation water contribut-
ing to root zone requirement. It indicates how well the irrigation system can deliver
and apply water to the crop root zone. Hence, the application efficiency takes into
account losses such as runoff, evaporation, spray drift, deep drainage, and applica-
tion of water outside the target crop areas. Of these factors, deep drainage and runoff
are probably the major causes of inefficiency and are generally due to overwatering.
Whenever more water is applied than can be beneficially used by the crop, water is
wasted and efficiency is low.
Application efficiency defined by different researchers varies slightly in the
ered to the field that is ready for crop use. As the application efficiency is a measure
of how efficiently water has been applied to the root zone of the crop, this parameter
relates the total volume of water applied by the irrigation system to the volume of
water that has been added to the root zone and is available for use by the crop. Thus,
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