Agriculture Reference
In-Depth Information
5.3.3 APPLICATION EFFICIENCY
The application efficiency (AE) is an indicator of water that is lost during the process
of supplying water to the field due to evaporation and wind drift losses. It is defined
as the volume of water applied to the surface divided by the volume of water exiting
the sprinkler emitter. The Eq. (3) is used to determine the AE is in a CU test. In Eq.
(3), AE = Application efficiency (%); A = Plot area (m²); V
s
= Volume of the exiting
emitter during CU test (m³); and m = Mean application depth (mm). The volume of
AE > 75% is always strived for.
AE =
100 ×
{(m × A)
÷
(V
s
)}
(3)
5.3.4 STATISTICAL UNIFORMITY
The statistical uniformity (SU) for micro and drip systems is determined by using the
coefficient of variation (CV), as defined in Eq. (4) where: SU = Statistical uniformity
(%); and CV = Coefficient of variation defined in Eq. (5). The SU which is >95% is
considered excellent. The SU of >85% is considered as good.
SU =
100
(1 - CV)
(4)
⎡
n
⎤
(
)
∑
CV
=
1/
X
{1 /
(1
−
nx
)} {
(
Xi
−
X
)}
2
(5)
⎢
⎥
⎣
⎦
i
=
1
5.3.5 EMISSION UNIFORMITY
The emission uniformity (EU) characterizes the uniformity of micro systems and is
defined in Eq. (6),
(
)
Qlq
⎡
⎤
(6)
EU
100
=×
1
−
1.27
CV
÷
n
x
[
]
Qavg
⎣
⎦
where: EU = Emission uniformity; CV = Manufacturers' coefficient of variation; n
= Number of emitters; Q
q
= Average low-quarter emitter discharge (l/h); and Q
avg
=
Overall average of emitter discharge (l/h).
5.4 METHODOLOGY
The environment in which irrigation farmers must function has changed significantly
in recent years because of changes in legislation that regulates the use of water in
South Africa. The National Water Act (Act 36 of 1998) provides for: Water resources
to be developed; and for water to be protected, used, conserved and controlled in a
sustainable and equitable manner.
The objective of the research for fi eld evaluation was therefore to quantify the
performance of the irrigation systems and to assist in improving the effi ciency of wa-
ter application by the irrigators. Evaluations were based on the standards by Ameri-
can Society of Agricultural and Biological Engineers (ASABE) and these evaluations
were expressed in terms of the uniformity coeffi cients.
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