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This page represents a version of Composting that existed whilst I was attempting to update the existing text whilst largely retaining the information in the format as of the version from November 2012.
Talk:Composting/editedversion_11-12 gives my thinking of that version.
As can be seen by the difference between this page and the current page, I had expanded the introduction and changed some of the sections. I eventually decided that the introduction was too long and distributed the text throughout the relevant sections. I also decided that the original sections made no sense to a new novice person wanting to come to appropedia to read about composting, hence there was no justification in keeping them as they were. I determined that this page would be best to introduce terms and direct users to other pages for further explanation. Therefore it needed to say something about microbes, something about the purpose of composting, something about the C/N ratio and something about different kinds of composting at different scales. All of these are explained in more detail on other pages on appropedia. Joeturner 01:50, 8 February 2013 (PST)
Composting, is the partial decomposition of organic materials by aerobic microbes. This has the effect of "stabilising" the nutrients, sanititising pathogens in the organic material and producing a useful soil amendment. This can be considered to have a long term fertilising effect on the soil, but may also be considered to have other useful properties - for example as mulches, composts added to the soil surface may prevent weed growth.
Successful composting requires a mix of organic materials as large amounts of high N (nitrogen) material will lead to high losses of N and other undesirable processes. As a rule of thumb, a target ratio of carbon: nitrogen should be 30:1 or lower. Materials which are high in N, such as animal manures, human sewage sludge, food wastes etc should therefore be mixed with large amounts of materials which are high in carbon, such as straw, wood, sawdust etc.
Due to the amorphous nature of composting, the mix of air within a heap may be poor. This may mean that there are parts of the compost which are actually anaerobic, and pathogenic microbes are more likely to survive in anaerobic conditions. Frequent mixing and turning of compost is therefore essential.
High or low levels of moisture may also have a big effect length of time it takes for the compost to stabilise.
Around the world, there are many examples of different ways of composting, however the most effective systems are usually fairly large, as larger compost heaps (sometimes called windrows) retain heat from microbial activity for longer, which is an important consideration when using composting for treatment of sludges which may contain pathogens. Smaller scale sites are easier to establish, but require careful attention and management to ensure the C:N ratio is maintained, the materials do not get too wet (or dry) and that the materials are regularly turned to ensure aeration. There are a range of designs of small bins and containers which mix materials and aerate or aggitate them.
Stabilised compost is dark in colour (exact colour will depend on the materials used), consistent (in the sense that it is hard to identify what was used to make it), is fairly fine and does not contain many contaminents (such as pieces of plastic, large pieces of wood etc). In most places with good management, stable compost can be produced within 8 weeks. However systems which are not ideal (sometimes known as 'cold composting') may take a lot longer. Composting toilets should be left to mature for at least a year after use and may still not be fully stable.
Like all organic matter additions, compost can add valuable plant nutrients to the soil to help plants grow and stay healthy. One advantage of composts are that they are often more stable than sludges and other materials, so may be less of a threat to water courses. In addition, the nutrients in compost may be in a form which is more appropriate for agriculture, however care must be taken when applying to soil as the compost may not be able to supply nutrients to the crop at the time or in the amount required. As a consequence, composts should be carefully considered as a part of a sustainable soil management system with other amendments.
Compost piles and windrows are made according to a specific ratio of carbon materials to nitrogen. This ratio should generally be 30:1, C:N. The carbon/nitrogen ratios of different materials are explained in In-depth explanation of bin composting.
In ideal conditions, the rapid respiration of microbes within the compost will lead to high temperatures and so this is sometimes refered to as 'hot composting'. Higher temperatures are highly desirable as it will denature pathogenic microbes (who are usually most active at around body temperature) and seeds of many species of weed.
There are several international standards regarding the times needed at particular temperatures for effective pathogen destruction. It has been proved that the best composting systems are able to elevate temperatures to these standards, however care should be taken as there may be variations within composting heaps (for example the edges of a heap are usually colder than the top middle). Several mixes may therefore be needed to ensure that all of the materials have reached the required temperatures. Unless temperatures have been regularly measured, and ideally microbial pathogens have been analysed, it should never be assumed that a particular compost mix has been able to kill off all pathogens, so composts including animal and human wastes should always be handled and used with caution.
- most of this is my text, some of it was built onto existing text. Joeturner 01:50, 8 February 2013 (PST)
===Pile or bin composting===
In fairly small scale composting, bins, piles and heaps are used. Bins may be produced from various different kinds of materials and can help to produce good compost if they assist with the flow of air through the heap. The disadvantage of bins is that the compost can be more difficult to turn and aerate. A heap on the ground can be seen as an easier option, however care may be needed to prevent the material from speading and to ensure it is adequately aerated.
- this is an altered version of the original section Joeturner 01:50, 8 February 2013 (PST)
Often people making compost use a recipe, often arrived at by trial-and-error, which is known to produce good compost in their situation.
This is one recipe using a layering technique
Layer the pile by alternating the previously mentioned "brown" and "green" layers. The ideal way to layer materials is by first loosening the ground on which the pile will be located to allow for drainage. The first layer should be a stalky material to allow for air flow and drainage, sunflower stalks, corn stalks, small branches or twigs work well for this. Then add a significant amount of dry vegetation or carbon such as leaves or straw. After that comes the nitrogen layer, which is green waste or kitchen scraps topped with a thin sheet of soil. The process is then repeated leaving out the stalky layer. If there is enough material, it is best to make the whole pile at once. For really cold climates a pile should be 4x4x4 feet to insulate it, but in a mild climate 3x3x3 feet is sufficient. A pile will shrink to about a fourth of the size and usually takes 3-6 months to fully break down. You will know that a pile is done when it is rich in color, falls apart easily in your hand, and you can not discern any of the original contents.
- the quoted text was from the original to make it clear that it is a personal opinion/recipe. Joeturner 01:50, 8 February 2013 (PST)
Whilst strictly speaking there is no need to layer the materials in a compost heap, a recipe such as this ensures that there is a good mix of different kinds of organic materials in the compost. Even with a recipe such as this, the compost should be examined regularly and changes made wherever necessary.
It is also often advisable to use several bins if there is a reasonable amount of organic material to be composted as it is easier to turn and mix compost from one bin to another. 'Turning' is the process of mixing the composts and allowing air to circulate around. Turned composts are usually better than those which have not been turned.
- my text to explain that this is just an opinion Joeturner 01:50, 8 February 2013 (PST)
... Sometimes is also makes sense to compost in windrows even if there is to be mixing and turning by hand.
- I was thinking about how much to say about windrows Joeturner 01:50, 8 February 2013 (PST)
=== Green manures and mulches ===
Green manures and mulches are sometimes thought of as composts, although they may not be.
'Green manure' is the process of growing a specific crop with a view to turning it into the soil, where it will break down. In some climates, it is often advisable to grow green cover crops in the Winter to prevent leaching and erosion of bare soil, which are then turned into the soil in the Spring. Sometimes uncomposted green organic material is spread onto the soil surface and ploughed in. As suggested above, this may not be ideal and a better option might have been to properly compost the material instead.
Mulching is a technique where a thick layer of material is placed on the soil surface to prevent regrowth of weeds between rows or around plants. Although slow release materials are often used as mulches - such as leaves and wood chippings - it can often make sense to use composts as a mulch.
Materials that are not organic in origin, such as old carpets, have sometimes been attempted as simple mulches. Their use is not advised because even carpet made of natural fibres can take a very long time to break down in the soil and removal can be a time consuming and annoying process.
- This was an attempt to improve the section which was originally titled 'layer composting'. I eventually decided this was better explained on the mulching page and removed it. Joeturner 01:50, 8 February 2013 (PST)
- The following was under ==Troubleshooting a pile==:
* Make sure you increase the amount of air regularly by turning it over.
As you still need to discard these somehow, you can opt to compost them anaerobically (using a biogas digester).
- This was re not putting in meat and fish. Advice on what to do with these scraps would be good (e.g. would a well-secured worm be suitable?) but a biogas digester is not always practical. --Chriswaterguy 16:35, 7 February 2013 (PST)
- Agreed. I think in the absence of proven technology, the best thing you can do is to burn or bury meat scraps. Otherwise they are an unacceptable risk of disease and attract vermin. I am not sure about bones - presumably it is possible to dry and grind them into something useful. Joeturner 01:50, 8 February 2013 (PST)