Agriculture Reference
In-Depth Information
and (iii) the general use of very efficient
irrigation techniques, such as drip irrigation
or the recirculation in soilless crops (Jolliet,
1999). Proper climate management can
improve the WUE in greenhouses (Sánchez-
Guerrero et al ., 2008).
The water use to produce 1 kg of toma-
toes in the Mediterranean area is of the
order of 60 l in intensive open field cultiva-
tion (Stanhill, 1980) and between 32 and
44 l in unheated low-tech greenhouses
(Castilla et al ., 1990b), whereas in the glass-
houses with climate control of Northern
Europe, with substrate and recirculation of
the drainage water, it goes down to 15 l
(Stanghellini, 2003). We can, therefore, state
that the greenhouse WUE is, at least, double
or triple that of open field.
These efficiency differences between
open field and greenhouse crops can be
much higher in extensively irrigated crops,
where the general water distribution (gen-
eral irrigation networks, channels, etc.) is
usually quite inefficient.
Regarding the economic efficiency of
the use of water, expressed as total income
for the grower (euros) per water unit used
(cubic metre), vegetable open field culti-
vation in Almeria reached a value of
€1.60 m −3 , whereas in greenhouses it was
€6.12
11.6.8
Quality of the irrigation water
The quality of the irrigation water is deter-
mined by the dissolved concentrations of
the different ions. The most common indi-
ces to classify irrigation waters are the elec-
tric conductivity of the water ( EC w ), which
is a function of the total ionic content and
quantifies the water salinity, and the sodium
absorption ratio (SAR), which measures its
alkalinity. See Appendix 1 section A.8.2.
11.7
Fertilization
11.7.1
Introduction
In protected cultivation, the cost of fertili-
zation is small in relation to the vegetable
production costs (see Chapter 14), so fertili-
zation has been usually high, as growers
have no incentives to save fertilizers and
pretend, mistakenly in many cases, that the
crop did not suffer any kind of nutrient defi-
ciency. Nevertheless, nowadays, the trend
to minimize the environmental impact has
resulted in the adoption of the so-called
'good agricultural practices (GAP) code' (see
Chapter 16).
m −3
(Colino
and
Martinez-Paz,
2002).
From the social point of view, we can
talk about the social WUE (in terms of
hours of labour generated per cubic metre
of water used). For vegetable cultivation in
the south of Spain the figure for labour
generated per cubic metre of water used in
greenhouses is 0.24 h m −3 compared with
0.09 h m −3 in the open field (Colino and
Martinez-Paz, 2002).
Several growing techniques contribute
to the improvement in the WUE, such as
carbon enrichment (Sánchez-Guerrero et al .,
2003) or the use of properly managed mobile
shading (Lorenzo et al ., 2003).
The use of fogging in the greenhouse
mitigates the negative effects of the irriga-
tion water salinity on yield, but requires
good quality water and, although it decreases
the ET, the total water use is higher (Montero
et al ., 2003).
11.7.2 The nutrients cycle
(soil cultivation)
In horticulture, and especially in green-
houses, there is more leaching of nitrates
than in other agricultural systems, due to
the high supplies, the high contents of
organic matter in the soil and the surplus
irrigation in relation to the ET c (Dasberg,
1999b). Its environmental impact can be
notable, mainly, in the surface and under-
ground aquifers.
The applications of nitrogen fertilizers
in the greenhouses normally exceed the
crop's requirements, increasing the risks of
nitrate leaching to the aquifers (Thompson
et al ., 2002).
Directive 91-676 of the European
Union regulates the protection of waters
against pollution caused by nitrates in
 
 
 
 
 
 
 
 
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