Agriculture Reference
In-Depth Information
Figure 4.4 represents the climate dia-
gram for Almeria. The solar radiation in
December is at the minimum limit. The tem-
peratures are slightly lower than 12°C (mini-
mum threshold) in the month of January,
which denotes that it would be necessary to
heat the greenhouse during this month.
Except for the summer months (June, July,
August and September), the remaining
months have thermal conditions which are
suitable for protected cultivation (between
12 and 22°C), with efficient ventilation. In
summer, it is necessary to limit the thermal
excesses to cultivate inside greenhouses.
Obviously, this method constitutes only
a primary approach to evaluate the climate
suitability of a region for the cultivation of
thermophilic vegetable species. In a similar
way, we can evaluate the climate suitability
of a certain location for greenhouse cultiva-
tion of other less thermally demanding spe-
cies (e.g. lettuce, Chinese cabbage).
The use of screens instead of plastic
films as a covering material, which do not
create a greenhouse effect and cause a shad-
ing effect and a windbreak effect, is an option
for protected cultivation which is being used
in low rainfall areas with mild winter tem-
peratures (e.g. the Canary Islands or tropical
American areas) or during the summer sea-
son in the uplands of medium latitudes (i.e.
the province of Granada, Spain).
4.5.1
Introduction
The name 'plastics' comes from the main
characteristic of these types of material
which is their plasticity, or capacity to be
moulded or shaped. The plastics are com-
posed of macromolecules (polymers), made
by the union of other smaller molecules
(monomers), obtained in the industrial
process of polymerization, and various
additives. If the polymer is made of just one
30
j
j
m
25
a
Almeria
(Spain)
a
20
m
s
15
f
Radiation
threshold
o
10
j
8.46
n
d
D
5
C
A
B
E
F
0
2
7
12
17
22
27
Mean monthly air temperature (°C)
A. Heating required
B. Protected cultivation possible without heating but with natural ventilation (passive)
C. Open air cultivation possible (inland areas)
D. Open air cultivation possible (coastal areas)
E. Need to use techniques to decrease temperatures
F. Excessive temperatures
Fig. 4.4.
estimation of the climate suitability of Almeria (Spain, 37°N) for the cultivation of thermophilic
vegetable species in greenhouses, from the monthly average values of air temperature and solar
radiation (adapted from Nisen
et al
., 1988).
