Second Nature: On Composting

Having only recently discovered an early, critically acclaimed gardening book by none-other-than Michael Pollan, I feel compelled to share interesting and educational passages from it as I encounter them. The book is called Second Nature: A Gardener's Education and the following is MP's take on composting circa 1991:

"Some gardeners, and even some garden writers, talk about compost as if it were fertilizer, but that is only part of the story, and it is somewhat misleading. It is true that compost contains nitrogen, phosphorus, and potash (the principal ingredient of fertilizer), but not in terribly impressive quantities. The real benefits of compost lie in what humus - its main constituent - does to the soil. Consider:

1.) Compost improves the soil's "structure." Soil is made up of clay, sand, silt, and organic matter, in varying proportions. Too much clay or silt, and the soil tends to become compacted, making it difficult for air, water, and roots to penetrate. Too much sand, and the soil's ability to retain water and nutrients is compromised. An ideal, friable garden soil consists of airy crumbs in which particles of sand, clay and silt are held together by humic acid. Compost helps these particles form. 
2.) Compost increases the soil's water-holding capacity. One experiment I read about found that 100 pounds of sand will hold 25 pounds of water, 100 pounds of clay will hold 50 pounds, and 100 pounds of humus will hold 190 pounds. A soil rich in compost will need less watering, and the plants growing in it will better withstand drought.
3.) Because it is so dark in color, compost absorbs the sun's rays and warms the soil.
4.) Compost teems with microorganisms, which break down the organic matter in soil into the basic elements plants need.
5.) Because it is made up of decaying vegetable matter, compost contains nearly every chemical plants need to grow, including such trace elements as boron, manganese, iron, copper, and zinc, not often found in commercial fertilizer. Compost thus returns to the soil a high proportion of the things agriculture takes out of it."

The book is fantastic, folks. Everyone who has ever worked on, played on, owned, tilled, raked, fertilized (**cringe**), seeded, mowed, plowed and otherwise enjoyed or despised any piece of land will appreciate Pollan's insights and reflections.