Agriculture Reference
In-Depth Information
is also of high salinity. The decrease in the
evaporation of the soil water with mulching
techniques limits the capillary rise of water
and salts, decreasing the problems derived
from salinity. The absence of rain in green-
houses (except in shelters with perforated
covers) decreases the possibilities of salt
leaching. In addition, the high doses of ferti-
lizers used can generate saline conditions.
The use of a sand layer over the soil,
characteristic of the 'enarenado' technique
(used in the south-east of Spain), plays the
role of mulching, decreasing evaporation
from the soil and allowing the use of slightly
saline irrigation waters, without yield
reduction.
In this 'enarenado' (sand mulching)
technique manure is also applied, in quanti-
ties of up 100 t ha
−1
, incorporating part of it
into the soil and leaving the rest in a uni-
form layer over the soil. The addition of a
sand layer, of 7-10 cm thickness, over the
manure finalizes the preparation of the
'enarenado' (Castilla
et al
., 1986).
The root development in the sand-
organic matter-soil interfaces reaches high
values of root density (much higher than
those measured in the soil). These high den-
sities can be of great interest for the crop,
providing good aeration of the roots in soils
of low permeability (Castilla
et al
., 1986).
supply the nutrient solution (drip irrigation,
sub-irrigation, circulating water, trays or
floating tables or aeroponics); or (iii) a func-
tion of the use of drainage (open or free
drainage systems and closed or recircula-
tion systems) (Winsor
et al
., 1990).
The proper hydroponic systems most
commonly used are: (i) the nutrient film
technique (NFT); (ii) the deep flow tech-
nique (DFT); (iii) the floating raft tech-
nique (FRT) in which cultivation takes
place on floating polystyrene boards; and
(iv) aeroponics. All of these are closed
systems. In the NFT a thin layer of nutri-
ent solution flows through gutters that
contain the roots (Cooper, 1979). The
method known as NGS (new growing sys-
tem) can be considered as a variant of
NFT. In the floating systems, trays made
of light-weight synthetic materials float
over a nutrient solution. In the aeroponics
systems the plants are cultivated in perfor-
ated plastic pads, which separate the aer-
ial part from the roots, which remain in
the dark in an enclosure where nutrient
solution is fogged with a very high fre-
quency. The aeroponic systems are seldom
used commercially.
However, the substrate-based systems
are the ones that have received widespread
use in horticulture (Plate 21); a brief descrip-
tion follows.
10.3
Soilless Cultivation
10.3.2
Advantages and disadvantages
of substrate-grown crops
10.3.1
Introduction: systems
Soilless cultivation is the system in which
the plant develops its root system in media
(normally solid or liquid) confined in a lim-
ited and isolated space, away from the soil
(Abad and Noguera, 1998). Nowadays, the
term hydroponics which properly refers to
water culture (hydroculture), is confused
with all the methods and techniques to cul-
tivate plants out of soil in artificial sub-
strates or in well-aerated nutrient solutions
(hydroculture) (Pardossi, 2003).
Hydroponic crops may be classified as:
(i) a function of the type of substrate or con-
tainer; (ii) a function of the method used to
The main reasons for the expansion of crops
grown on substrates have been to avoid soil-
borne diseases (in contaminated greenhouses,
mainly, by monoculture) and for the good
agronomic performances of the crops with
these systems (Urban, 1997b). Furthermore,
with the development of substrate technolo-
gies and improvement in their management
they may improve the efficiency in the use of
water and nutrients (closed systems), and
also contribute to a reduction in several crop
cultural practices in the management of the
soil (Penningsfeld and Kurzmann, 1983;
Savvas and Passam, 2002).
