Agriculture Reference
In-Depth Information
Photo 11.5.
Meteorological station inside a greenhouse.
The lack of uniformity in applying the
water will involve an extra water supply (in
total
R
b
, gross water requirements) to cover
the net water requirements (
R
n
). The water
application efficiency coefficient (
E
a
, lower
than 1.0) expresses the ratio between the
water stored in the soil profile available for
the roots and the applied water:
E
a
= K
s
×
E
u
(11.7)
where
K
s
is a coefficient that quantifies
the soil's water storing efficiency (which
is of the order of 0.9 in sandy soils and 1.0
in loamy or clay soils) and
E
u
is a coeffi-
cient that reflects the uniformity in the
emission of water (in a well-designed and
well-managed irrigation system,
E
u
=
0.85-0.95). The calculation of the uni-
formity coefficient of a certain facility is
easy to perform (Castilla and Montalvo,
1998; Castilla, 2000).
In the case of using saline water, it is
necessary to add a complementary amount
of water to ensure the removal of the salts.
This leaching fraction (dependent on the
salinity of the water used, represented by
LF
) is the minimum amount of drainage
required to maintain the soil salinity
between certain limits that do not involve
yield loss.
In surface or sprinkler irrigation (Ayers
and Westcot, 1987):
EC
w
(11.8)
LF =
5
EC
−
EC
e
w
where:
EC
w
= Electric conductivity of the irrigation
water (dS m
−1
)
EC
e
= Electric conductivity of the soil's
saturated extract, adapted to the degree of
tolerance expressed as the expected yield
(as a percentage of the maximum yield)
in Table 11.4.
In the case of HFLI (Ayers and Westcot,
1987):
EC
w
LF =
2
(11.9)
Max
EC
e
where:
Max
EC
e
= Maximum electric conductivity
tolerable of the soil's saturated extract for
that specific crop (see Table 11.4).
Once
LF
is known, the gross water
requirement (
R
b
) is:
R
R =
E LF
n
(11.10)
b
(1
−
)
a
In systems of low uniformity, scarce
supply of water or saline waters, with the
aim of reducing the large losses due to
