Agriculture Reference
In-Depth Information
(a)
(c)
(b)
Fig. 4.5.
Irrigation of orchards has moved away from furrow and
fl
ood irrigation to
the use of drip tubes (a) and micro-sprinklers (b). To determine water needs a simple
system is the use of tensiometers at different depths (c). Electrical tensiometers are
also available.
that the plants do not become water-stressed, resulting in improved yields
(Baldini, 1992). The systems represent a higher initial investment, and skilled
labour is needed to install and maintain, with the benefi ts of lower water usage
and greater ei ciency of application. In many parts of the world, these systems
lend themselves to 'fertigation' or 'ferti-irrigation', a combination of irrigation
and fertilization. A calibrated mixer injects a fi xed amount of a concentrated
liquid fertilizer stock solution into the main irrigation supply line. The amount
injected is determined by knowing the amount of water to be applied, fl ow rate
and the amount of concentrated fertilizer to meet the plant's needs.
Sprinkler irrigation
Sprinkler irrigation is still quite popular for fruit trees. Permanent and semi-
permanent or portable sprinkler systems are used. Sprinkler irrigation can
be over or under the tree canopy (Fig. 4.5b). The above-canopy system
washes pesticides of the leaves and can contribute to disease spread because
of the humidity and splashing the droplet causes. In the case of banana and
plantain, under-canopy irrigation is used. Mini-sprinklers that cover a circle
with a diameter of about 12-14 m are installed every 10-11 m in a square
arrangement. Under-canopy irrigation avoids the disadvantages of the big
sprinklers used in the past, which covered almost 1 ha. In very few situations,
