Agriculture Reference
In-Depth Information
1
1.1
Introduction
The lack of water is the most important
limitation for all agricultural activity. Losses
caused by drought are about equal to those
induced by all other climatic factors
together, including excess of water, floods,
cold, hail and wind (Boyer, 1982). Irrigation
is, without doubt, the most ancient method
to protect crops (from drought) and has per-
mitted agricultural activity in arid and
desert regions that, without irrigation,
would not be productive. Nowadays pro-
tected cultivation goes far beyond providing
irrigation, to include several plant protec-
tion techniques, and has reached an enor-
mous importance during the last century.
Protected cultivation is a specialized agri-
cultural system in which a certain control of
the soil-climate ecosystem is exercised
modifying its conditions (soil, temperature,
solar radiation, wind, humidity and air
composition). Plants are cultivated by
means of these techniques modifying their
natural environment to prolong the harvest-
ing period, alter the conventional cropping
cycles, increase yields, improve product
quality, stabilize production and provide
products when open field cultivation is lim-
ited (Wittwer and Castilla, 1995).
The main goal of protected cultivation
is to obtain high value products (vegetables,
fruits, flowers, ornamentals and seedlings).
The most relevant determining factor of
horticultural production activity is the cli-
mate. Among the most important limita-
tions for horticultural production are the
low solar radiation conditions, the unfa-
vourable temperature and humidity condi-
tions, unfavourable water and nutrient
levels, presence of weeds, excessive wind
and an inadequate concentration of carbon
dioxide (CO
2
) in the air. The majority of the
above-mentioned limitations are climatic
factors or factors directly related to the cli-
mate, which may be altered by means of
protected cultivation.
All vegetable species have an optimal range
for each environmental parameter. Placing a
screen near the plant modifies the environ-
mental conditions affecting the whole or
part of the plant.
The position of the screen or other sim-
ilar protection, in relation to the plant,
determines the type of protection (CPA,
1992). When the screen is placed over the
soil and under the aerial parts of the plant,
we call it mulch (Photo 1.1). Lateral screens
or forms of protection are referred to as
windbreaks (Photo 1.2). When the screens
