Compost (or US /ˈkɒmpoʊst/) also known as brown manure, is the aerobically decomposed remnants of organic matter. It is used in landscaping, horticulture and agriculture as a soil conditioner and fertiliser. It is also useful for erosion control, land and stream reclamation, wetland construction, and as landfill cover (see compost uses).
Compost serves as a growing medium,or a porous, absorbent material that holds moisture and soluble minerals, providing the support and nutrients in which most plants will flourish. To maximize plant growth, it is sometimes necessary to dilute compost with soil or peat to reduce salinity or to add neutralisers to bring the pH closer to 7, or additional nutrients like fertilisers or manure, wetting agents, and materials to improve drainage and aeration, such as sand, grit, bark chips, vermiculite, perlite, or clay granules.
Composting as an alternative to landfill
As concern about landfill
space increases, worldwide interest in recycling
by means of composting is growing, since composting is a widely accepted process for converting decomposable wastes of biological origin into stable, sanitized products useful for horticulture. The more recent application of composting for large-scale waste reduction has very little in common with organic farming. The 1999 European Landfill Directive
put pressure on European states to meet specified targets for landfill reduction, principally by establishing alternate disposal and treatment of organic materials. While certain countries such as Belgium, Holland, Germany and Austria readily achieved the mandated targets, other countries such as the UK, Spain and Italy have not. Indeed, it is commonly accepted that the UK, despite its early important contributions to organic farming
and John Innes Compost
, started taking composting seriously only after Brussels threatened a penalty for states not attaining the required reduction targets. A recent National Audit Office
report for England warned that councils were in danger of missing EU targets to cut the amount of waste at landfills. The NAO's report stated that to meet European targets for 2010, a reduction in the UK of at least 3.5m tonnes of biodegradable waste sent to landfill was needed. A reduction of a further 3.7m tonnes was needed by 2013. Less than one-half this has been currently met.
Modern large-scale composting should therefore not be confused with an idealistic, organic-oriented goal to recycle and improve soils; since, for most western countries now, it is virtually the law. These factors could lead to a conflict between required production of composts and the quality of the product.
Given enough time, all biodegradable
material will compost, and the primary objective in the modern push to compost is to capture readily degradable materials so they do not enter landfill. However, most small-scale domestic systems will not reach sufficiently high temperatures to kill pathogens
and weed seeds or deter vermin
, so pet droppings, scraps of meat
, and dairy products
are often best left to operators of high-rate, thermophilic
composting systems. Your local green waste recycling facility should operate such a system. Cooked food, meat, fish and dairy can all be safely thrown on a home compost heap only if they have first been fermented with bokashi
Nevertheless, hobby animal manure (horses, goats), vegetable kitchen and garden waste are all excellent raw material for home composting. Early roots of composting as a treatment for municipal solid waste
were spurred by awareness of the trash crisis as early as the 1950s, and the rise worldwide of large MSW composting plants in the 1960s into the 1970s was virtually unregulated.
Public outcry in Europe against contamination of soils on farms and vineyards from MSW compost containing residues of plastic, metals and glass triggered a shakeup of the industry, and in the 1980s a phasing out of MSW composting,
European composting standards
An overview of European efforts to attain compost standardisation can be seen on the European Compost Network
(ECN) . The British Composting Association
has established very recently a set of guidelines for compost, called the BSI PAS 100
listed by the British Standards Institute
(PAS stands for "Publicly Available Specification
" and is not necessarily an adopted or certified standard). There are a variety of such voluntary industry standards in Europe and worldwide, such as the German Bundegütegemeinschaft Kompost e.V. (BGK) German Compost Association
RAL-standard for compost developed 10 years prior to the British standard, and updated recently to include separate standards for fermented by-products(from biogas
reactors) and sludge. In America, Procter & Gamble
Company sponsored the U.S. Composting Council (USCC
) in the early 1990s to develop compost process and product standards called "TMECC", still in a draft state. These standarisation programs (guidelines would be a better word than standards to describe the objective) are intended to provide structure in the composting community for handling the entire composting process from raw materials and production methods, through quality control and lab testing. Swiss compost guidelines recognize distinct end-uses of composts, as determined by specific laboratory assays (see VKS-ASIC-ASAP-ASCP Swiss Compost Association
Compost types and ingredients
There are different ways to compost, starting with layers of 'brown' and 'green' biodegradable waste mixed with garden soil. 'Brown' waste refers to carbon-rich materials, such as, straw, cardboard egg boxes and hedge clippings. 'Green' waste refers to nitrogen-rich biodegradable waste that breaks down faster, such as fruit and vegetable peelings, coffee grounds, cut flowers, and grass clippings.
Vermicomposting, uses worms, most often tiger worms, to help quickly break down organic waste.
Composting Coffee Grounds
Composting coffee grounds can add nitrogen to the soil. A long term study done by Cindy Wise at the Oregon State University Extension Service has documented the use of coffee grounds in a variety of ways since 2001. To provide an idea of the scale of the coffee ground resource, the study estimates that Lane County, Oregon produces 1 million pounds (453,593 kgs) of coffee grounds annually. Coffee grounds usually have close to a neutral pH of 7.0. Compost piles with 25% coffee grounds by volume appear to heat up to higher temperatures (135-155 DegF) and stay hot longer periods. These higher temperatures help to kill weed seeds. This is similar to composting with animal manure. An important observation is that using uncomposted coffee grounds in a garden bed will be detrimental to plants. An experiment found 25% coffee mixed in a garden bed caused stunted growth in seedlings.
Compost End Uses
Compost is almost universally recommended as a soil improver. It is principally intended as an additive to soil or other matrices such as coir and peat, (although it may also be used to make compost tea). High rates of mixture (e.g. 80–100%) of compost have been occasionally noted in growing media, but generally direct seeding into a compost is not recommended. It is very common to see blends of 20–30% compost used for transplanting seedlings at cotyledon stage or later.
The primary factors controlling how well a compost blend performs are salinity and maturity, which singly and together can trigger phytotoxicity symptoms. It is well known that high salt content in growing media will affect water relations of plants, especially in early stages of growth. The effects or symptoms of damage can be yield reduction, leaf deformation and tip-burning or even plant epinasty.
These effects can also be attributed to a variety of other factors that may be present in active or finished composts, depending on ingredients. Such elements include pesticides, presence volatile fatty acids which are by-products of anaerobic conditions or residues of anaerobic digestion, ammonia associated with high manure content, heavy metals such as copper from farm ingredients and sludge, and ethylene oxide from plant debris, any of which can trigger some form of stunting and other phytotoxicity traits. In container-mix studies, it has been demonstrated that immature compost deprives the soil of oxygen content for a significant period of time, resulting in stunting of roots.
As a result of these numerous challenges, the introduction of compost products into professional horticulture as a competition to peat and soil-based products has been significantly less successful than originally hoped for. A Jan 2008 consumer report in the UK severely criticised compost quality, showing that only one out of 24 composts tested against 4 cultivars in actual growing media trials could be recommended as viable "peat-free" product. Nevertheless, the broad popularity of composts and their long term beneficial effects for soils and crops mean that demand will continue to grow worldwide.
- Insam, H; Riddech, N; Klammer, S (Eds.): Microbiology of Composting ,Springer Verlag, Berlin New York 2002, ISBN 978-3-540-67568-6
- Hogg, D., J. Barth, E. Favoino, M. Centemero, V. Caimi, F. Amlinger, W. Devliegher, W. Brinton., S. Antler. 2002. Comparison of compost standards within the EU, North America, and Australasia. Waste and Resources Action Programme Committee (UK) (see wrap.or.uk)