Agriculture Reference
In-Depth Information
Table 13.1
Compost ingredients
Proposed ingredient
Category
Cardboard
Brown
Farmyard manures
Intermediate
Fibrous prunings
Brown
Haulm (old plants)
Brown
Hedge clippings
Intermediate
Herbaceous plants (old)
Brown
Grass mowings
Green
Grass - long
Brown
13
Kitchen (plant) waste
Green
Leaves - young
Green
Leaves - autumn
Brown
Nettles - young
Green
Figure 13.3
Compost bins. A typical set large enough
for effi cient composting; slatted to allow in air and
removable so as to allow easy access to add new
material and for regular turning of the contents
Nettles - old
Brown
Paper
Brown
Sawdust
Brown
Seaweed
Green
Straw
Brown
rates can be restored by 'turning' the compost
heap on a regular basis to improve aeration. This is
continued until all that is left is a crumbly material
with no recognizable plant material and an 'earthy'
smell.
Woody prunings
Brown
such that aeration is maintained and waterlogging
avoided.
X
pH
(see p. 174) - the compost mix should not be
too acid. Thin layers of lime (see p. 000) can be
added as the heap is built.
X
Temperature
-
the rate at which the organisms
decompose the organic matter also depends
on the temperature of their environment. The
composting process gives off heat (exothermic
reaction); under ideal circumstances the
temperature can rise to over 70°C within seven
days. However, most garden composting does not
go to a high enough temperature to kill harmful
organisms and weed seeds.
X
Heap size
-
heat is generated within the volume
of the heap by the exothermic process but it is
lost from the surface so the degree to which the
compost heats up depends on the surface area
to volume ratio. Small heaps (less than a cubic
metre) have a disproportionally large surface area
which dissipates the heat generated within the
small volume so the heap does not heat up ('cold
composting'). Insulation reduces heat loss from
the surfaces but this also reduces the fl ow of air
(oxygen) into the heap.
Organic waste brought together in large enough
quantities under ideal conditions heats up quickly,
but the process then tends to slow down because
the availability of oxygen becomes reduced.
Rather like stirring up the dying embers of a fire (i.e.
getting oxygen around unburnt fuel), decomposition
Garden (home) composting
Most gardeners are not usually able to obtain
enough components at any one time to create the
ideal compost heap. It is difficult to be successful
with batches less than one cubic metre at a time;
the cooling at the surfaces is greater than the heat
generation at the centre. Compost bins can be
purchased but slatted wooden sided bins can be
made (see Figure 13.3). An open base over soil allows
organisms and air in. It is advantageous to have a
second bin alongside so that the compost heap can be
turned from one to the other frequently (slats between
the two should be removable to make 'turning' easier).
A suitable cover (e.g. old carpet) is needed to keep
warmth in and rain off.
This is a 'cold' method that can produce good
compost but tends to take many months or even a
year or two to complete. When making compost this
way, care should be taken to avoid perennial weeds or
infected plant material which is unlikely to be rendered
harmless.
Compost tumblers
These are containers that can be rotated on an axis
to provide an easy method of turning small batches
to create compost in a relatively short time (see
Figure 13.4). Batches can heat up sufficiently to kill off
