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!
