Municipal composting schemes usually must process huge volumes of material on very valuable land close to cities.  Economics mean the heaps are made as large as possible, run as fast as possible, and gotten off the field without concern for developing their highest qualities.  Since it takes a long time to reduce large proportions of carbon, especially when they are in very decomposition-resistant forms like paper, and since the use of soil in the compost heap is essential to prevent nitrate loss, municipal composts tend to be low in nitrogen and high in carbon.  By comparison, the poorest home garden compost I could find test results for was about equal to the best municipal compost.  The best garden sample ("B”) is pretty fine stuff.  I could not discover the ingredients that went into either garden compost but my supposition is that gardener “A” incorporated large quantities of high C/N materials like straw, sawdust and the like while gardener “B” used manure, fresh vegetation, grass clippings and other similar low C/N materials.  The next chapter will evaluate the suitability of materials commonly used to make compost.

Analyses of Various Composts

Source N% P% K% Ca% C/N

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.