Vegetable trimmings & paper 1.57 0.40 0.40 24:1
Municipal refuse 0.97 0.16 0.21 24:1
Johnson City refuse 0.91 0.22 0.91 1.91 36:1
Gainsville, FL refuse 0.57 0.26 0.22 1.88 ?
Garden compost "A" 1.40 0.30 0.40 25:1
Garden compost "B" 3.50 1.00 2.00 10:1
To interpret this chart, let's make as our standard of comparison
the actual gardening results from some very potent organic material
I and probably many of my readers have probably used: bagged chicken
manure compost. The most potent I've ever purchased is inexpensively
sold in one-cubic-foot plastic sacks stacked up in front of my local
supermarket every spring. The sacks are labeled 4-3-2. I've
successfully grown quite a few huge, handsome, and healthy
vegetables with this product. I've also tried other similar sorts
also labeled "chicken manure compost" that are about half as potent.
From many years of successful use I know that 15 to 20 sacks (about
300-400 dry-weight pounds) of 4-3-2 chicken compost spread and
tilled into one thousand square feet will grow a magnificent garden.
Most certainly a similar amount of the high analysis Garden "B"
compost would do about the same job. Would three times as much less
potent compost from Garden "A" or five times as much even poorer
stuff from the Johnson City municipal composting operation do as
well? Not at all! Neither would three times as many sacks of dried
steer manure. Here's why.
If composted organic matter is spread like mulch atop the ground on
lawns or around ornamentals and allowed to remain there its nitrogen
content and C/N are not especially important. Even if the C/N is
still high soil animals will continue the job of decomposition much
as happens on the forest floor. Eventually their excrement will be
transported into the soil by earthworms. By that time the C/N will
equal that of other soil humus and no disruption will occur to the
soil's process.
Growing vegetables is much more demanding than growing most
perennial ornamentals or lawns. Excuse me, flower gardeners, but
I've observed that even most flowers will thrive if only slight
improvements are made in their soil. The same is true for most
herbs. Difficulties with ornamentals or herbs are usually caused by
attempting to grow a species that is not particularly well-adapted
to the site or climate. Fertilized with sacked steer manure or
mulched with average-to-poor compost, most ornamentals will grow
adequately.
But vegetables are delicate, pampered critters that must grow as
rapidly as they can grow if they are to be succulent, tasty, and
yield heavily. Most of them demand very high levels of available
nutrients as well as soft, friable soil containing reasonable levels
of organic matter. So it is extremely important that a vegetable
gardener understand the inevitable disruption occurring when organic
matter that has a C/N is much above 12:1 is tilled into soil.
Organic matter that has been in soil for a while has been altered
into a much studied substance, humus. We know for example that humus
always has a carbon to nitrogen ratio of from 10:1 to about 12:1,
just like compost from Garden "B." Garden writers call great compost
like this, "stable humus," because it is slow to decompose. Its
presence in soil steadily feeds a healthy ecology of microorganisms
important to plant health, and whose activity accelerates release of
plant nutrients from undecomposed rock particles. Humus is also
fertilizer because its gradual decomposition provides mineral
nutrients that make plants grow. The most important of these
nutrients is nitrate nitrogen, thus soil scientists may call humus
decomposition "nitrification."
When organic material with a C/N below 12:1 is mixed into soil its
breakdown is very rapid. Because it contains more nitrogen than
stable humus does, nitrogen is rapidly released to feed the plants
and soil life. Along with nitrogen comes other plant nutrients. This
accelerated nitrification continues until the remaining nitrogen
balances with the remaining carbon at a ratio of about 12:1. Then
the soil returns to equilibrium. The lower the C/N the more rapid
the release, and the more violent the reaction in the soil. Most low
C/N organic materials, like seed meal or chicken manure, rapidly
release nutrients for a month or two before stabilizing. What has
been described here is fertilizer.
When organic material with a C/N higher than 12:1 is tilled into
soil, soil animals and microorganisms find themselves with an
unsurpassed carbohydrate banquet. Just as in a compost heap, within
days bacteria and fungi can multiply to match any food supply. But
to construct their bodies these microorganisms need the same
nutrients that plants need to grow--nitrogen, potassium, phosphorus,
calcium, magnesium, etc. There are never enough of these nutrients
in high C/N organic matter to match the needs of soil bacteria,
especially never enough nitrogen, so soil microorganisms uptake
these nutrients from the soil's reserves while they "bloom" and
rapidly consume all the new carbon presented to them.
During this period of rapid decomposition the soil is thoroughly
robbed of plant nutrients. And nitrification stops. Initially, a
great deal of carbon dioxide gas may be given off, as carbon is
metabolically "burned." However, CO2 in high concentrations can be
toxic to sprouting seeds and consequently, germination failures may
occur. When I was in the seed business I'd get a few complaints
every year from irate gardeners demanding to know why every seed
packet they sowed failed to come up well. There were two usual
causes. Either before sowing all the seeds were exposed to
temperatures above 110 degree or more likely, a large quantity of
high C/N "manure" was tilled into the garden just before sowing. In
soil so disturbed transplants may also fail to grow for awhile. If
the "manure" contains a large quantity of sawdust the soil will seem
very infertile for a month or three.
Sir Albert Howard had a unique and pithy way of expressing this
reality. He said that soil was not capable of working two jobs at
once. You could not expect it to nitrify humus while it was also
being required to digest organic matter. That's one reason he
thought composting was such a valuable process. The digestion of
organic matter proceeds outside the soil; when finished product,
humus, is ready for nitrification, it is tilled in.
Rapid consumption of carbon continues until the C/N of the new
material drops to the range of stable humus. Then decay
microorganisms die off and the nutrients they hoarded are released
back into the soil. How long the soil remains inhospitable to plant
growth and seed germination depends on soil temperature, the amount
of the material and how high its C/N is, and the amount of nutrients
the soil is holding in reserve. The warmer and more fertile the soil
was before the addition of high C/N organic matter, the faster it
will decompose.
Judging by the compost analyses in the table, I can see why some
municipalities are having difficulty disposing of the solid waste
compost they are making. One governmental composting operation that
does succeed in selling everything they can produce is Lane County,
Oregon. Their _yard waste compost_ is eagerly paid for by local
gardeners. Lane County compost is made only from autumn leaves,
grass clippings, and other yard wastes. No paper!
Yard waste compost is a product much like a homeowner would produce.
And yard waste compost contains no industrial waste or any material
that might pose health threats. All woody materials are finely
chipped before composting and comprise no more than 20 percent of
the total undecayed mass by weight. Although no nutrient analysis
has been done by the county other than testing for pH (around 7.0)
and, because of the use of weed and feed fertilizers on lawns, for
2-4D (no residual trace ever found present), I estimate that the
overall C/N of the materials going into the windrows at 25:1. I
wouldn't be surprised if the finished compost has a C/N close to
12:1.
Incidentally, Lane County understands that many gardeners don't have
pickup trucks. They reasonably offer to deliver their compost for a
small fee if at least one yard is purchased. Other local governments
also make and deliver yard waste compost.
So what about your own home compost? If you are a flower,
ornamental, or lawn grower, you have nothing to worry about. Just
compost everything you have available and use all you wish to make.
If tilling your compost into soil seems to slow the growth of
plants, then mulch with it and avoid tilling it in, or adjust the
C/N down by adding fertilizers like seed meal when tilling it in.
If you are a vegetable gardener and your compost doesn't seem to
provoke the kind of growth response you hoped for, either shallowly
till in compost in the fall for next year's planting, by which time
it will have become stable humus, or read further. The second half
of this book contains numerous hints about how to make potent
compost and about how to use complete organic fertilizers in
combination with compost to grow the lushest garden imaginable.