Agriculture Reference
In-Depth Information
formed are leached deep into the soil over the winter
and can be lost from the root zone.
Farmyard manure is most valued for its ability to
provide the organic matter and humus for maintaining
or improving soil structure. It must be worked into
soils where conditions are favourable for its continued
decomposition. If fresh organic matter is worked into
wet and compacted soils or deep into clay, the need
for oxygen outstrips supply and anaerobic conditions
prevail to the detriment of any plants present. These
soils develop grey colouring and a foul ('bad eggs')
smell.
composting vessels, the most common issues are
contamination with plastics and glass.
Spent mushroom compost
This compost is a by-product of the mushroom
industry, that is, it is the 'spent' (i.e. used) material
that becomes available direct from the growers
or some garden centres. It used to be made from
well-rotted horse manure but now it is almost all
composted straw capped with chalk, which gives its
characteristically high pH, that is, basic reaction (see
p. 174). This makes it useful for raising soil pH as an
alternative to liming (see p. 176). It works well with
the growing of calcicoles (see p. 174) especially when
growing brassicas (cabbages, cauliflowers, Brussels
sprouts).
It is an excellent source of organic matter with added
nutrients left over from mushroom growing with
which to mulch or to incorporate in the soil but its use
is limited. It must not be used in plants that prefer
acid conditions (see calcifuges, p. 174). If used too
freely, nutrient deficiencies in plants can be induced
(see iron-induced chlorosis, p. 171) leading to poor
performance. Leftover fertilizer levels in the sample
can make it unsuitable for young plants particularly
when growing in containers.
Garden (home) compost
The main advantage of garden compost is that it is
the most convenient way of recycling garden and
kitchen waste without the need for transport. If well
made, an attractive crumbly dark brown material
becomes available for use as a soil conditioner,
ideally as a mulch (see p. 160). This helps to protect
the surface from soil capping (see p. 150), maintains
organic matter levels in the soil and supplies
nutrients in a slow-release form (see p. 173). It can
be the basis of 'no-dig' and bed systems of growing
(see p. 150).
Alternatively, it can be worked into the soil, providing
many of the same advantages but requiring further
work to incorporate. This is a better option if the
compost has not been heated sufficiently to kill weed
seeds. It has too many problems to be used alone as a
compost for seed production, but well-made material
can be used mixed with other materials to make
potting composts.
Instead of composting in a bin, the garden waste can
be shredded and distributed directly on to the soil
as a mulch where it will decompose given the right
conditions (as in the natural world). This achieves the
same result, often more quickly, and without the need
for managing the process in bins.
Leaf mould
Leaf mould is made of the rotted leaves of deciduous
trees and makes a highly prized compost. The leaves
are often composted separately from other organic
matter and much valued in ornamental horticulture
for a variety of uses such as an attractive mulch or,
when well-rotted down, as a compost ingredient. They
are commonly composted in mesh cages, but many
achieve success by putting them in polythene bags
well punched with holes. The leaves alone have a high
brown to green ratio so decomposition is slow (see
organic matter mix p.160). Usually it is not until the
second year that the dark brown crumbly material is
produced, although the process can be speeded up by
shredding the leaves first
.
It is low in nutrients because nitrogen and phosphate
are withdrawn from the leaves before they fall and
potassium is readily leached from the ageing leaf.
Unless they are from trees growing in very acidic
conditions, the leaves are rich in calcium and the
leaf mould made from them should not be used with
calcifuge plants (see p. 174).
Composted municipal waste
This is essentially the same as garden compost, but
because it can be composted in bulk it has normally
been heated sufficiently to inactivate harmful weeds
and plant diseases. The product is usually too high
in nutrients to be used alone in growing composts.
The high wood content gives the final product good
stability (see p. 179), but can lead to nitrogen lock-
up. It has a high pH (see p. 172), but it can be mixed
with composted barks, coir and so on to create
good container compost for a wide range of plants.
However, unless the composting is done in high-cost
