Agriculture Reference
In-Depth Information
3.5.3.3 Design Steps and Procedures
(1) Determine the daily maximum supply requirement for an area (
A
) for the target
crop as
A
×
ET
max
E
a
V
A
=
(3.28)
where
Required volume of water for the area
A
(m
3
)
V
A
=
Specific area that is to be irrigated (m
2
)
ET
max
=
A
=
Daily maximum evapotranspiration (m)
Design application efficiency of the sprinkler
ET
max
can be calculated as
E
a
=
ET
max
=
K
c
×
ET
0
(3.29)
where
K
c
=
crop-coefficient at peak water demand period
ET
0
=
reference evapotranspiration at peak water demand period
Note
: For specific application, when some soil moisture deficit is allowed, ET can
be calculated as follows:
ET
max
=
K
c
×
K
s
×
ET
0
(3.30)
where
K
s
is the soil moisture stress coefficient.
Detailed procedure for calculating ET
0
and ET has been described in
Chapter 7
(
Field Water Balance
), Volume 1.
(2) Determine discharge rate (
Q
)forthearea
A
based on the minimum operating
hour.
V
A
(m
3
)
t
(h)
Q
A
(m
3
/h)
=
(3.31)
(3) Optimize sprinkler and lateral spacing for the individual sprinkler discharge rate
and application rate (which is constrained by the soil infiltration rate) from the
following relationship:
q
=
S
m
×
S
l
×
I
(3.32)
where
S
l
=
sprinkler spacing along laterals (m)
S
m
=
lateral spacing along mainline (m)
I
=
average application rate (m/h)
discharge rate for the individual sprinkler (m
3
/h) [for the area
(
S
m
×
q
=
S
l
)m
2
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