Agriculture Reference
In-Depth Information
with soil, are used. These drains slow the rate of water fl ow and allow the
water to infi ltrate into the soil. In most cases, swales are left open and they
carry the water to a main ditch or creek. In heavy rains, these shallow swales
are overloaded and can lead to signifi cant erosion.
Raised beds are recommended when root rot-susceptible crops such as
papaya, passion fruit, avocado and pineapple are grown on level land (Fig.
3.3). The deep furrows created between the beds drain away the excess water
(Fig. 3.3a). These furrows can be used for irrigation during the dry months.
In fi elds with depressions or under wet or in heavy soils, planting the tree on
a mound reduces the problems due to waterlogging (Fig. 3.3b). The mound
height depends upon the magnitude of the fl ooding problem, with around
25 cm being common. Taller mounds increase the orchard layout costs and
consideration should be given to fi eld-levelling grading, leaving only a gentle
slope. Levelling or land shaping is practised in some pineapple-growing areas.
The shaping is done with heavy machinery by making a successive series of
wide and not very steep mounds so that the excess rainwater runs into their
lower parts, to be drained from the fi elds. This shaping maybe done in addition
to the use of raised beds that are oriented so that their furrows conduct water
to the lower parts of the fi eld.
The banana industry is very sophisticated in its drainage infrastructure
in the wet tropics. Bananas do not tolerate a high water table or long periods
of soil saturation. A successive series of parallel, open drains 1.2-2.5 m
deep every 40-60 m, referred to as tertiary drains, are dug. These drains are
designed to keep the water table at the desired depth and also to collect runof
that is not absorbed by the soil. Shallow drains (quaternary drains) are dug
(a)
(b)
Fig. 3.3.
Drainage is a major concern for tropical tree fruit production in areas with
high water tables or heavy rains. Trees are grown on raised beds (a) and planted on
mounds (b).
