fall to earth where soil-dwelling organisms consume them and each
other until eventually there remains no recognizable trace of the
original plant. Only a small amount of humus is left, located close
to the soil's surface or carried to the depths by burrowing
earthworms. Alternately, the growing plants are eaten by animals
that do not live in the soil, whose manure falls to the ground where
it comes into contact with soil-dwelling organisms that eat it and
each other until there remains no recognizable trace of the original
material. A small amount of humus is left. Or the animal itself
eventually dies and falls to the earth where ....

Composting artificially accelerates the decomposition of crude
organic matter and its recombination into humus. What in nature
might take years we can make happen in weeks or months. But compost
that seems ready to work into soil may not have quite yet become
humus. Though brown and crumbly and good-smelling and well
decomposed, it may only have partially rotted.

When tilled into soil at that point, compost doesn't act at once
like powerful fertilizer and won't immediately contribute to plant
growth until it has decomposed further. But if composting is allowed
to proceed until virtually all of the organic matter has changed
into humus, a great deal of biomass will be reduced to a relatively
tiny remainder of a very valuable substance far more useful than
chemical fertilizer.

For thousands of years gardeners and farmers had few fertilizers
other than animal manure and compost. These were always considered
very valuable substances and a great deal of lore existed about
using them. During the early part of this century, our focus changed