Compost and The Living Soil

by Steven Wisbaum

While many gardeners have some idea about the importance of using compost, not as many truly understand what makes compost so valuable. To better appreciate the magic of compost, it helps to understand how soil fertility is created in more natural ecosystems such as forests and grasslands.

Though modern conventional agriculturists came to view the soil as a lifeless anchor for plant roots, we now understand that the soil is actually a highly complex ecosystem dependent on oxygen, water, and a dazzling array of organisms. These organisms - which include bacteria, fungi, protozoa, algae, actinomycetes, nematodes, earthworms and a host of insects - are ensured a never-ending supply of nutrients and chemical energy in the form of plant debris and animal excrement that falls to the soil surface. Once accessible to these soil-dwelling organisms, these complex organic compounds are metabolized into simpler forms that can then be utilized by growing plants. A familiar by-product of this subterranean digestive process is a substance known as humus.

Now consider the soils in a typical garden or farm where the native vegetation is removed, the crops are harvested, and soil compaction from people and machinery reduces both the oxygen and water holding capacity of the soil. Additional impacts include the use of synthetic fertilizers - which are toxic to many soil organisms - and mechanical or manual cultivation which further depletes organic matter through increased oxidation, erosion, and exposure to UV-radiation. Ultimately, the collective impacts of these forces lead to a depleted and lifeless soil media which in-turn results in unhealthy plants with only minimal resistance to pests, diseases, and draught.

Recognizing that it takes thousands of years to create the deep, fertile soils found in nature, the liberal use of compost (along with crop rotation, green manuring, etc.) has become the cornerstone of a biological approach to agriculture. Aside from containing large amounts of pre-digested organic matter (humus), compost contains a virtual cornucopia of stable plant nutrients as opposed to the soluble and biologically reactive forms contained in synthetic fertilizers and raw manure. Compost that has been uniformly composted at temperatures above 130F. and then sufficiently cured is also free of the weed seeds and pathogens associated with raw or improperly composted materials. Furthermore, the humus in compost also differs substantially from the undigested carbonaceous materials found in uncomposted raw manure or plant debris which will stunt plant growth by temporarily immobilizing nitrogen supplies in the soil. And finally, compost is also chock full of beneficial microbes which stimulate biological activity in the soil and is increasingly being found to suppress a wide variety of soil-borne plant diseases.