What is Compost

A Manufactured Product:

The practice of composting is not strictly a natural process. No-where in nature do compost heaps naturally or spontaneously occur. Autumn leaves may gather and decay but despite their apparent similarity they are not compost heaps. Composting occurs when another organism deliberately gathers up material and constructs it so as to encourage a rapid explosion of specific micro-organisms. Just as bread is not simply a combination of flour and water baked into a rock but is the product of the controlled growth of a specific micro-organism (namely yeast) so compost is also the product of the controlled growth of specific micro-organisms: principally the thermopile (heat loving) and mesophile (warm loving) bacteria.

A Modern Process:

Whilst there are some early references to compost (1600’s) and in the late 1800’s Paris disposed of its manure and organic wastes in the market gardens that surrounded it; thus giving rise to modern horticulture, this was more often 17th and 19th Century waste disposal than the considered and controlled manufacture of compost. Composting in the modern sense did not begin until the early 20th Century, where it formed a major part of the ‘Humus Theory‘, and like many things in science it happened in a lot of places at once: It flowered. Perhaps the most significant “bloom” occurred in the 1920’s at the Indore Research Station, Indore, Central India where Sir Albert Howard developed the Indore process of composting. (Howard 1940). Howard, particularly in the English speaking World was the first to look at composting not just as a means of returning or disposing of wastes but as a major factor in managing and improving soil fertility and crop production.

A Three Phase Process:

Composting, unlike the leaven bread analogy, is not the result of a single process or single organism but the controlled growth and succession of organisms. Each stage serves a purpose and prepares the compost material (substrate) for the next. These stages are: a thermophilic (hot), a mesophilic (warm) and a stabilisation or curing stage (cool) and it is the control and co-ordination of these three processes that results in good quality compost or horrible smelly muck.

A Living Product:

Perhaps the biggest misconception with compost is it’s true biological state. Because compost is made with dead organic material and has an appearance similar to mineral earth it is similarly regarded as being an inert and relatively dead material. However quite the reverse is true. It is this ‘livingness‘ of compost that one is attempting to cultivate and exploit through the process rather than the elemental constituents of the contributing raw materials.

These raw materials are the feed stocks upon which the microbial communities proliferate, and with optimum conditions growth rates can be exceptional. It has been estimated that in a single gram of compost in excess of 10 billion individual organisms or Colony Forming Units (CFU) can proliferate and it is this, the microbial biomass and what it can contribute rather than the feed stocks used that the composter is interested in. Similarly it has been argued that under optimum conditions the entire substrate can become utilized by and into the microbial biomass so that there is only microbial material and none of the original feed stock remains.

Thus contrary to popular belief compost is not decayed and dead plant material but organic material that has been converted into microbial biomass by the process of composting. A process that similarly occurs in the soil but at much slower and under more erratic and less efficient conditions.

Whilst all 22 nutrients that a plant needs for growth are to some degree present in a finished compost it is to the availability of the elements of Nitrogen, Phosphorus and Sulphur that compost principally contributes too.

Thus we see that compost is not a ‘natural process’ in the true sense, for it does not spontaneously occur in nature, nor is the end product an inert material. Compost in the 21st Century is a modern three phase manufacturing process that produces a greatly enhanced microbial biomass that can be utilised to maximise the availability of Nitrogen, Phosphorus and Sulphur (the biotic nutrients of the 3-4-5 Nutrient model) in agriculture situations.

next: Compost container construction, principles of manufacture


Free Cultural Works (CC-BY-NC-SA) Malcolm McEwen 2011

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