Agriculture Reference
In-Depth Information
this further to identify and quantify the
environmental impacts of these systems, so
that there was greater understanding of their
total economic value and their social
productivity.
2000 and 2260 kg ha −1 of PE, every 2 or 3
years in the south of Spain (Escobar, 1998),
and whose recycling is nowadays almost
universal (Photo 14.5). Other plastic materi-
als, of much less importance, are the films
used for double roofs and mulching as well
as the polypropylene strings and waste irri-
gation dripper lines.
Plant waste is of enormous importance
in those areas where the density of green-
houses is high. Its removal at the end of the
growing cycles (Photo 14.6) generates waste
volumes ranging from 40 to 60 m 3 ha −1 for a
watermelon crop and from 130 to 150 m 3
ha −1 for a tomato crop (Escobar, 1998). If
expressed in fresh weight, the estimation of
the residues may reach 55 t ha −1 for pepper
or 40 t ha −1 for tomato and aubergine, with
initial moisture of 85% (Parra et al ., 2001).
To eliminate plant waste, composting and
controlled combustion (with cogeneration
of electric energy, for instance) are the sys-
tems of most interest (Parra et al ., 2001).
Recently another option has been intro-
duced that of biofumigation.
Substrate cultivation generates residues
in the order of 75 m 3 ha −1 of rockwool or
128 m 3 ha −1 of perlite, as an average, every
2 or 3 years, depending on their shelf life
(Escobar, 1998).
14.2.2
Most important residues
The environmental impact of irrigation water
leachates in agricultural systems has already
been described (Tanji, 1980; Stewart and
Nielsen, 1990). In the specific case of green-
houses, substrate cultivation allows for the
use of closed systems, which recirculates the
drainage water reusing it for irrigation and
avoiding the environmental impact associ-
ated with the leachates and subsequent pol-
lution of the underground aquifers.
Sustainable management of the green-
house soil is more complex than in conven-
tional agriculture, mainly because of the
lack of crop rotation and due to crop inten-
sity, which enhances the possibility of salin-
ity problems and, in the case of low quality
water, increases the danger of salinization
and alkalinization of the soil.
Plastic residues consist mainly of green-
house cover films, which amount to between
Photo 14.5. The recycling of plastic greenhouse cover film residues is common in the south of Spain.
 
 
 
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