Composting is an environmentally friendly way to deal with garden and food waste which also saves money, improves soil structure, recycles nutirents and helps to keep the garden looking nice. This post describes the processes which occur during composting and answers the question ‘what is compost?’.
The simplest way to make compost from waste is by simply putting the waste into a compost heap. As long as there is moisture present the composting process occurs spontaneously. However, many people prefer to use compost bins to keep the composting area tidy and to avoid attracting rodents.
Composting is the decomposition of organic matter, aided by invertebrate animals such as earthworms and various microbes, into compost, which is comprised of humus. Humus is a dark, sticky substance containing stable organic chemicals which will not undergo any further short term decomposition. Humus contains a wide variety of chemicals derived from those present in living organisms including humic acid which is not a single organic acid but a combination of many organic acids containing carboxyl and phenolate functional groups.
An important part of answering the question ‘what is compost’ is to describe what it starts out as being. Basically anything that constitutes an ‘organic waste’ can be composted, that is, anything that was once alive. This includes paper and cardboard, which come from wood. Types of organic waste which can be made into compost include garden waste like grass cuttings and leaves, fruit and vegetable rinds, paper and cardboard, egg shells, saw dust, herbiverous animal droppings like horse manure, tea bags and coffee grounds. Including meat, cooked food or dog faeces into a compost mixture tends to attract vermin and most home composting systems do not incorporate these types of organic waste.
The composting process involves several kinds of microorganism. Bacteria feed on carbon based materials to produce carbon dioxide and nitrogen compounds, with heat being generated in the process. It is important for composting mixtures to be exposed to sufficient oxygen levels so that the organic materials are broken down by aerobic bacteria because anaerobic bacterial action on the compost produces nasty smells and chemical byproducts which are not beneficial. Keeping the compost aeriated can be achieved by turning with a fork. It is also necessary to keep the contents of the compost heap or compost bin moist but not saturated as the bacteria themselves only feed on chemicals which are dissolved in water. Fungi assist in the breaking down of wood lignins found in bark, which are themselves consumed, along with bacteria, by protozoa in the compost heap.
Earthworms help to aeriate the compost heap, whilst digesting partially decomposed material and adding nutritious vermicompost or ‘worm poo’ to the mixture. There are also other invertebrates which help with the composting process called rotifers. These are tiny animals which are mostly less than a millimeter long and which help to control the microbial populations in the compost bin.
One of the important bacterial groups present in the garden compost heap is called actinomycetes. These bacteria help to digest the cellulose from rotting plants and chitin from the bodies of invertebrate animals in the compost heap. This group of bacteria is known to produce naturally occurring antibiotics including streptomycin which has been used to treat bacterial infections including tubercolosis and plague!
I hope this article adequately answers the question ‘what is compost’, whilst providing some insight into the organisms which make the process possible.