Here's a simple arithmetic problem that illustrates how to balance
carbon to nitrogen.
_QUESTION:_ I have 100 pounds of straw with a C/N of 66:1, how much
chicken manure (C/N of 8:1) do I have to add to bring the total to
an average C/N of 25:1.
_ANSWER:_ There is 1 pound of nitrogen already in each 66 pounds of
straw, so there are already about 1.5 pounds of N in 100 pounds of
straw. 100 pounds of straw-compost at 25:1 would have about 4 pounds
of nitrogen, so I need to add about 2.5 more pounds of N. Eight
pounds of chicken manure contain 1 pound of N; 16 pounds have 2. So,
if I add 32 pounds of chicken manure to 100 pounds of straw, I will
have 132 pounds of material containing about 5.5 pounds of N, a C/N
of 132:5.5 or about 24:1.
It is far more sensible to learn from experience. Gauge the
proportions of materials going into a heap by the result. If the
pile gets really hot and stays that way for a few weeks before
gradually cooling down then the C/N was more or less right. If,
after several turnings and reheatings, the material has not
thoroughly decomposed, then the initial C/N was probably too high.
The words "thoroughly decomposed" mean here that there are no
recognizable traces of the original materials in the heap and the
compost is dark brown to black, crumbly, sweet smelling and most
importantly, _when worked into soil it provokes a marked growth
response, similar to fertilizer._
If the pile did not initially heat very much or the heating stage
was very brief, then the pile probably lacked nitrogen. The solution
for a nitrogen-deficient pile is to turn it, simultaneously blending
in more nutrient-rich materials and probably a bit of water too.
After a few piles have been made novice composters will begin to get
the same feel for their materials as bakers have for their flour,
shortening, and yeast.
It is also possible to err on the opposite end of the scale and make
a pile with too much nitrogen. This heap will heat very rapidly,
become as hot as the microbial population can tolerate, lose
moisture very quickly, and probably smell of ammonia, indicating
that valuable fixed nitrogen is escaping into the atmosphere. When
proteins decompose their nitrogen content is normally released as
ammonia gas. Most people have smelled small piles of spring grass
clippings doing this very thing. Ammonia is always created when
proteins decompose in any heap at any C/N. But a properly made
compost pile does not permit this valuable nitrogen source to
escape.
There are other bacteria commonly found in soil that uptake ammonia
gas and change it to the nitrates that plants and soil life forms
need to make other proteins. These nitrification microorganisms are
extremely efficient at reasonable temperatures but cannot survive
the extreme high temperatures that a really hot pile can achieve.
They also live only in soil. That is why it is very important to
ensure that about 10 percent of a compost pile is soil and to coat
the outside of a pile with a frosting of rich earth that is kept
damp. One other aspect of soil helps prevent ammonia loss. Clay is
capable of attracting and temporarily holding on to ammonia until it
is nitrified by microorganisms. Most soils contain significant
amounts of clay.
The widespread presence of clay and ammonia-fixing bacteria in all
soils permits industrial farmers to inject gaseous ammonia directly
into the earth where it is promptly and completely altered into
nitrates. A very hot pile leaking ammonia may contain too little
soil, but more likely it is also so hot that the nitrifying bacteria
have been killed off. Escaping ammonia is not only an offensive
nuisance, valuable fertility is being lost into the atmosphere.
_Weather and season. _You can adopt a number of strategies to keep
weather from chilling a compost pile. Wind both lowers temperature
and dries out a pile, so if at all possible, make compost in a
sheltered location. Heavy, cold rains can chill and waterlog a pile.
Composting under a roof will also keep hot sun from baking moisture
out of a pile in summer. Using bins or other compost structures can
hold in heat that might otherwise be lost from the sides of
unprotected heaps.
It is much easier to maintain a high core temperature when the
weather is warm. It may not be so easy to make hot compost heaps
during a northern winter. So in some parts of the country I would
not expect too much from a compost pile made from autumn cleanup.
This stack of leaves and frost-bitten garden plants may have to
await the spring thaw, then to be mixed with potent spring grass
clippings and other nitrogenous materials in order to heat up and
complete the composting process. What to do with kitchen garbage
during winter in the frozen North makes an interesting problem and
leads serious recyclers to take notice of vermicomposting. (See
Chapter 6.)
In southern regions the heap may be prevented from overheating by
making it smaller or not as tall. Chapter Nine describes in great
detail how Sir Albert Howard handled the problem of high air
temperature while making compost in India.