Agriculture Reference
In-Depth Information
impermeability to water and gases; and
(vi) its transparency to light.
Its low cost, in particular, has permitted
the displacement of traditional materials
in some applications (in greenhouses or
mulches) and the generation of new uses that
previously did not exist, such as tunnels,
direct covers or drip irrigation, among others.
A good knowledge of the limitations of
the use of plastics (see Chapter 4) will allow
for better use of them: for instance, under
extreme conditions of temperature (the ther-
mal stability of some plastics at low or high
temperature is not satisfactory). The static
electricity of some formulations, such as
ethylene vinyl acetate (EVA) or plasticized
polyvinyl chloride (PVC), induces the accu-
mulation of dust, which decreases transpar-
ency to light. The same effect is caused by
scratches on some materials if they are not
properly protected from the impact of winds
carrying sand. Other aspects, such as the
ageing of plastics (which affects how long
they can be used) and their behaviour against
fire, must be considered for optimum use.
In protected cultivation the solar radia-
tion transmission properties of the plastic
materials are of key importance for plant
growing (see Chapter 4).
modification of the natural environment
of plants, which totally or partially
alter the microclimate conditions, with
the aim of improving their productive
performance.
Among the protected cultivation tech-
•
niques, it is worth noting windbreaks,
mulches, low tunnels, direct covers, high
tunnels and greenhouses.
The main objectives of protected culti-
•
vation are, among others, to: protect the
crops from harmful temperatures, wind,
rain, hail and snow, as well as from
pests, diseases and predators, creating
a microclimate that allows for the
improvement of their productivity and
quality, contributing to a better use of
resources.
Protected cultivation has been used
•
for many centuries; references to the
use of protection date back to Roman
times.
The development of plastic materials
•
has contributed to the widespread use
of greenhouses and other protection
techniques, from the last third of the
20th century all over the world.
The estimated protected cultivation
•
area worldwide in 2010 was 1,905,000
ha of greenhouses, 1,672,000 ha of low
tunnels and floating covers and over
ten million ha of mulches. The huge
increase in area under protected culti-
vation in recent decades was due to the
enormous spread in Asia, mainly in
China.
1.7
Summary
•
The
name
'protected
cultivation'
involves a series of techniques for the
