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.