(Materials & methods to ensure quality
Just like people, compost organisms need
water to live. Some microorganisms use the
film of water to move—slipping and sliding
to another section of the pile. Biological
activity stops when the pile dries out.
If adequately aerated, composting material
with moisture content between 30% and 100%
will be aerobic. In practical aerobic composting,
however, high moisture content must be avoided
because water displaces air from the interstices
between the particles causing anaerobic conditions.
However, too low moisture content deprives
organisms of water needed for their metabolism,
and inhibits their activity.
Maximum moisture content for satisfactory
aerobic composting varies with materials
used. If straw and strong fibrous materials
are used, the maximum moisture content can
be much larger without destroying structural
qualities or causing material to become soggy,
compact and unable to contain enough air
in the interstices. But if it contains lots
of paper or grass clippings, which have little
structural strength when wet, or if granular,
like ash and soil, less water is better.
Ideally, home compost piles whould contain
40 - 60% moisture. It should feel as moist
as a wrung out sponge. Dry carbon layers
can be watered as the pile is built, then
with each turning, add more water as necessary.
In University of California studies, fibrous
materials containing an abundance of straw
were composted aerobically with moisture
contents of 85% to 90%, but other composts
containing much paper became anaerobic in
one day when the moisture content was about
If anaerobic composting is practiced, the
maximum moisture content is not as important,
since oxygen maintenance is not a factor.
The upper limit of moisture, which may be
from 80% to over 90%, is the amount of which
excessive drainage from the compost will
be produced. If the composting procedure
has initial aerobic conditions to produce
high temperatures lasting a few days for
the destruction of pathogenic organisms,
followed by anaerobic composting, the maximum
initial moisture content may be as high as
65% to 85%, depending on the character of
the composting materials.