Agriculture Reference
In-Depth Information
A hard layer or hardpan can be present in previously cultivated land (Fig.
3.2). These layers can develop in soils that have been cultivated with heavy
equipment when the soil was too wet or where the plough passed many times
at the same depth (plough pan). This hard layer (Fig. 3.2b) is eliminated by
subsoiling or ripping of the soil deeper than the hard layer (Fig. 3.2c). This
disruption of the hard layer (Fig. 3.2a and b) will allow better root penetration
into the subsoil. Subsoiling involves using a heavy tractor or bulldozer pulling
subsoiling hooks or rippers that are set to rip to 50-200 cm (Fig. 3.2c), with
a second pass done at a 45° angle to the fi rst pass (Fig. 3.2d). Some other
subsoiling techniques use a torpedo-shaped device that is pulled with a cable
and leaves an underground passage that improves water and air circulation.
This operation should normally be done when the soil is dry in order to be
ef ective.
Subsoiling and ploughing can be used to incorporate any fertilizer or
amendment to the soil. Typical amendments include manure to increase
organic matter, sulfur to lower the pH or lime to raise it, or any element that will
be in big demand can be incorporated at this time, when it is easier than after
planting. Phosphorus and other elements can also be incorporated deeper into
the soil and will be more ef ective, since mobility when applied on the surface
is very poor. If there are dif erent soil layers, then subsoiling will also help to
mix and homogenize the layers, with large pieces of roots from the previous
crop normally being removed. When a very hard underground 'caliche' layer
is present, subsoiling is not normally practised but a hole is made through the
layer using an auger or pointed steel rods to allow roots to penetrate further
(a)
(b)
(c)
Loosened soil
Leg
Pan broken up
Pan
Foot with wings
(d)
Restricted root
growth
Hardpan
Little root growth
Extensive root growth
down the soil profile
Fig. 3.2.
Root development of tree crops mainly occurs in the top metre of the
soil pro
fi
le (a); a hardpan can restrict root growth (b) and the hardpan needs to be
broken by a subsoiler (c). The tine of the subsoiler rips through the hardpan and
allows roots to penetrate. Subsoiling should be done with two passes of the
fi
eld at
about 45° to each other.
