Agriculture Reference
In-Depth Information
The coefficient
K
c
depends on the crop and
its vegetative stage and changes through the
crop cycle, increasing from lower values of
the initial stage (sowing or transplanting)
through the vegetative growth period, reach-
ing the highest values in the maximum
development period (when the crop covers
the soil, intercepting all the solar radiation)
and decreasing during senescence.
In Mediterranean plastic greenhouses,
values of the product (
K
p
×
K
c
) for several
crops have been estimated and are summa-
rized in Table 11.3.
The similarity of the values of the
product (
K
p
×
K
c
) with the
K
c
values in
several horticultural crops, according to
the literature (Doorenbos and Pruitt, 1976;
Veschambre and Vaysse, 1980) allowed for
the estimation that the
K
p
value in the
greenhouse is normally around 1.0. Later
studies (Fernández
et al
., 2001) stated that
K
p
was lower (around 0.8), but that the
K
c
values were higher than those provided
for open field crops, so their product is
very similar to the figures provided in
Table 11.3.
The evolution of the
K
c
values will
depend on the sowing or transplanting date
as a function of the climate conditions, but
it can also be estimated as a function of the
thermal integral of the leaf development
when the dates are different to those indi-
cated in Table 11.3 (Fernández
et al
., 2001;
Fernández, 2003).
Other methods for calculating
ET
0
that
are of interest in greenhouses are the radia-
tion and the adapted Penman-Monteith
methods, detailed in Appendix 1 section
A.8.3. In order to have proper greenhouse
climate data it is necessary to have a mete-
orological station in the area (Photo 11.5).
Gross irrigation requirements
Of the irrigation water applied only a part is
available to the roots, due to: (i) the runoff
losses (there may be none, for example in a
well-designed and well-managed drip irri-
gation system); and (ii) the almost unavoid-
able percolation or deep leaching required
where saline waters are used in order to
remove the salts from the root zone.
Table 11.3.
evolution of the product of the crop coefficient by the pan coefficient (
K
p
×
K
c
) per fortnight,
of some horticultural species, in unheated plastic greenhouses in Almeria, Spain, for indicated sowing (S)
or transplant (T) dates (Castilla, 1989).
Climbing
bean
Tomato
Pepper
Cucumber
Melon
Watermelon
Aubergine
Period
(days)
T: 16 Oct
T: 1 Sept
S: 16 Sept
S: 16 Jan
S: 1 Feb
S: 16 Sept
T: 1 Oct
1-15
0.25
0.20
0.25
0.20
0.20
0.25
0.20
16-30
0.50
0.30
0.60
0.30
0.30
0.50
0.35
31-45
0.65
0.40
0.80
0.40
0.40
0.70
0.55
46-60
0.90
0.55
1.00
0.55
0.50
0.90
0.70
61-75
1.10
0.70
1.10
0.70
0.65
1.00
0.90
76-90
1.20
0.90
1.10
0.90
0.80
1.10
1.10
91-105
1.20
1.10
0.90
1.00
1.00
1.00
1.05
106-120
1.10
1.10
0.85
1.10
1.00
0.90
0.95
121-135
1.00
1.00
-
1.10
0.90
-
0.85
136-150
0.95
0.90
-
1.00
-
-
0.80
151-165
0.85
0.70
-
-
-
-
0.80
166-180
0.80
0.60
-
-
-
-
0.80
181-195
0.80
0.50
-
-
-
-
0.80
196-210
0.80
0.50
-
-
-
-
0.80
211-225
-
0.60
-
-
-
-
0.80
226-240
-
0.70
-
-
-
-
0.60
241-255
-
0.80
-
-
-
-
0.60
