Agriculture Reference
In-Depth Information
which is covered by the crop. When the
crops are in the soil or in substrate at soil
level, the normal arrangement is one or two
main passages such as indicated in Fig. 12.5.
This arrangement is used for low-density
species, such as vegetables, because the
workers can access, by means of secondary
passages, any point in the greenhouse. It is
preferable to have a single main passage
on the north side (in the northern hemi-
sphere), as this is the coldest side. The sec-
ondary passages allow access to the different
zones to perform different crop-care tasks
(Fig. 12.5). In tall species, the secondary
passages are usually covered or almost com-
pletely covered by vegetation. In high den-
sity crops, such as carnation, that prevent
workers from passing between the plants, it
is normal to adopt a longitudinal arrange-
ment (Fig. 12.6).
However, the important point from
the productive point of view is the inter-
ception of solar radiation by the vegeta-
tion. The interception really determines
the real space occupancy coefficient, and
depends on the size of the species, as well
and the pruning and training techniques
used, as well as the density and the
arrangement of the plants.
In practice and in the majority of tall
crops the secondary passages (Fig. 12.5)
remain shadowed by the vegetation for
most of the day. In species that have
more-or-less horizontal leaves, radiation
is admitted to be conveniently intercept-
ed by several leaf strata when the leaf
area index (LAI) reaches a value of 3.0
(Berninger, 1989).
The orientation of the crop rows in a
north-south direction homogenizes the
radiation conditions between the plants,
which is especially relevant in some orna-
mental crops (phototropic plants).
When growing ornamental pot plants
or in nurseries, plants can be elevated on
tables or bedplates, of 0.8 m height, to
make tending the crop easier. In these
cases, the traditional arrangements of pas-
sages are longitudinal and peninsular when
the bedplates are fixed (Fig. 12.6). The
occupancy rate in the longitudinal arrange-
ment is slightly lower (around 65%) than
Photo 12.3.
Use of rails (heating pipes) to move
the lifting platform.
The use of small channels in which
water circulates, activated by a pump, in
which the harvested fruits are transported
floating to the packing house is another
alternative. This is used in sophisticated
greenhouses in northern countries, but
has not extended to other parts of the
world.
Robots employed in greenhouse oper-
ations are already used in nurseries and
pot plant production (Giacomelli
et al
.,
2008; Montero
et al
., 2010). Several auto-
matic systems have allowed for the maxi-
mization of the use of the greenhouse area
(see next section) minimizing labour
(Plate 24).
12.3.3
Occupancy of the greenhouse
The rate of occupancy of a greenhouse
describes the proportion of the total surface
