Agriculture Reference
In-Depth Information
plants. The size and stability of these
clumps/aggregates determines how well
water, air, soil animals and plant roots
move through the soil. Where there are
stable soil aggregates, water will be absorbed
easily, air can percolate to the roots and
plants can spend more of their energy on
shoot growth rather than forcing their roots
through hard soil. Aggregates should be
stable after rain and
not
form a hard crusty
top that prohibits penetration by anything but
a sharp spade or mattock!
(a)
(b)
The strong 'glue' that holds soil particles
together to form stable aggregates is
decomposed organic matter or humus. So
whatever soil you have, the addition of
composts and manures can only improve it.
These can be dug in, or on really concrete-
like clays, laid under a mulch covering in
autumn and dug through the soil profile by
earthworms. Too much digging will destroy
soil aggregates, so the use of rotary hoes will
obliterate a soil structure, creating a soil that
sets like concrete when it is dry and turns into
an amorphous slurry when it is wet. It sounds
contrary, but a bit of digging in of organic
matter will reduce the need to dig in the
future - but don't dig too much. Keep adding
organic matter and earthworms will happily
dig it through for you.
(c)
Figure 1.10
Different soils have different structure and
soil texture. A heavy clay (a) can be improved with
gypsum and organic matter resulting in a well-structured
soil with stable soil aggregates that hold water and
nutrients and allow the easy penetration of roots (b).
Gravelly sand cakes after rain and holds neither water nor
nutrients well (c).
Soil pH
Soil pH sounds technical but it isn't really. It is
a scale indicating the acidity or alkalinity of
the soil. Caustic soda (pH 14) is alkaline and
battery acid (pH 1) is of course acid - plants
will grow in neither as they are at the extreme
ends of the scale. Somewhere in the middle,
from pH 5.5 to pH 7.5, will be satisfactory for
These particles bunch together, creating
different sized spaces where water and air can
be stored, and they also provide a site for
nutrients to cling to. These are essential
ingredients for the successful growth of
