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Compost Potential
Why Compost?
It will become increasingly important for us as a nation to recycle organic material and nutrients
as much as possible. One nice way of achieving this and at the same time producing valuable
soil conditioner and even useful microbial products is to compost. It is good if there can be
coordination between livestock production that results in waste materials with horticultural
production that can then make excellent use of those wastes.
Hot Composting, Worms or Fermentation
There are an increasing number of ways in which a composting or fermentation can be
undertaken. In hot composting alone, methods range from low cost, low tech heaps (usually
turned) through to fully enclosed vertical or horizontal composting units. The choice there is
one of cost/benefit and how reliable the process has to be e.g. an enclosed unit may be
required if meat products are being composted. With worm composting, the worm itself is
the enclosed unit, a bioreactor that chews the material down to finer particles and provides
the right environment of moisture, pH and temperature for digestion by itself and by the
microorganisms inside and outside the worm. Worm casts and compost that worms have
been working through contain the most valuable and stable form of humus.
Liquid fermentation is something often unknowingly practiced in effluent ponds and can be
enhanced to provide higher quality liquid and less odour. Fermentation of solid organic wastes
is widely practised in Asia but offers some potential in this country. Good solid fermentation
can mean less loss of organic carbon, reduction of odour problems and potentially a higher
value microbial product.
Common hitches in Composting
Perhaps the most common cause for a composting operation to fail is for the compost to go
unintentionally anaerobic and smelly.
This will usually be the result of too
high a water content and or too fine
a material; it may require added straw
or sawdust and covering from rain
(don’t water it so much that water
can be easily squeezed out of the
material). A heap should be large
enough (usually at least 1m wide by
1 m high) to retain and build heat but
should also be turned at least twice
to prevent the inside areas running
low on oxygen.
If a compost heap is large enough
but still doesn’t heat up, it may be
short of nitrogen or water.
Compost heap at the BHU
Carbon and Nitrogen
Be liberal with the water to try to
make the compost materials 30%
moisture (or the consistency of a
damp sponge).
As far as balancing up the nitrogen,
the aim is a C:N ratio of 25 to 30.
Straw has a C:N ratio of something
like 100.
Chicken dung may be around 7;
so four times the amount of chicken
manure
(by weight) should be used to match
the straw for optimum composting.
As long as the aim is not microbial
extracts, the process of composting
is very forgiving and time fixes
imbalances. Sawdust alone will
eventually rot and go black, it just takes several years. An unintentionally anaerobic
compost will also eventually form nice humus especially if it gets subsequently turned.
Fertiliser value
While still not as high in nutrient
analysis as most chemical or
mineral fertilisers, if a compost is
left to mature fully (black, no longer
heating, original materials unidentifiable) it still contains a significant amount of plant materials.
There is significant loss of bulk with the concentration of nitrogen and other elements increasing
proportionally throughout the process. Full maturing also reduces the chance of a relatively
low nitrogen compost (e.g. too much sawdust, not enough manure) causing nitrogen deficiency
in crops.
Examining well made compost.
Note: Compost should be stored under cover
