Agriculture Reference
In-Depth Information
down the soil profi le and for water to drain to the subsoil. Dynamite has been
used to crack superfi cial rocky soils, especially if the rocks are of coralline
origin or calcareous; this was done in large areas in Cuba. A small hole the size
of the dynamite piece is bored into the rock and then exploded to crack the rock
and leave a passageway for water and roots to penetrate.
Stones can be another problem during land preparation, though not as
much as with annual crops. Ideally all rocks and stones should be removed,
especially from the soil surface, in order to ensure that the machinery will
have no problems in moving around and will not be damaged. In very stony
areas, removal is uneconomic and only large and medium stones on the
surface are taken from the fi eld so vehicles can move freely in the orchard and
mowing can be carried out. Stone removal should preferably be done after
subsoiling and ploughing, so that most large stones will be on the surface.
Often the stones are used to build boundary fences. Alternatively, the stones
are used to fi ll depressions, holes or ditches in the fi eld or throughout the farm.
The next step is ploughing the whole fi eld, sometimes in two directions, with
large stones again being removed. Ploughing is followed by discing to break
up the larger clods and make the fi eld ready for planting. Land levelling is
sometimes performed, especially if furrow irrigation is to be used; with drip or
micro-sprinklers this will not be necessary. If surface fl ood or furrow irrigation
is used, the furrows need to be cut at this time, along with soil fumigation, if
required, and planting holes made.
DRAINAGE
Drainage is needed for most orchards, especially when the land is fl at and the
soil has a low water percolation rate. Failure to provide drainage can mean
waterlogging and standing water remains in the fi eld for more than a few
hours. Standing water in fl ooded fi elds means that the soil atmosphere will
soon become depleted of oxygen and become anaerobic. Anaerobic conditions
cause stress to most tropical fruit tree roots, limit nutrient uptake and make
the roots less able to resist soil-borne pathogens such as root rots due to
Phytophthora
and other fungal pathogens.
Drainage is accomplished with ditches and sometimes with interconnected
subsurface drainage pipes. This can be an expensive investment. On gently
sloped land, plant rows are normally oriented to follow the maximum incline
so that the excess water fl ows downhill. This orientation is possible if the slope
does not exceed 10%. When the slope is greater than 10% transverse ditches
will be needed to slow down the water speed, and these transverse ditches are
connected to the main drainage ditches. In mountainous areas, tree rows
normally follow the contour, so as not to create an erosion problem when it
rains. Swales along the contour or 'French drains', which consist of a system
of ditches fi lled sequentially with stones and gravel and sometimes covered
