Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical and biological properties. It is commonly prepared by
decomposing plant, food waste, recycling organic materials and manure. The resulting mixture is rich in plant nutrients and
beneficial organisms, such as bacteria, protozoa, nematodes and fungi. Compost improves soil fertility in
garden
A garden is a planned space, usually outdoors, set aside for the cultivation, display, and enjoyment of plants and other forms of nature. The single feature identifying even the wildest wild garden is ''control''. The garden can incorporate bot ...
s,
landscaping
Landscaping refers to any activity that modifies the visible features of an area of land, including the following:
# Living elements, such as flora or fauna; or what is commonly called gardening, the art and craft of growing plants with a goal ...
,
horticulture
Horticulture is the branch of agriculture that deals with the art, science, technology, and business of plant cultivation. It includes the cultivation of fruits, vegetables, nuts, seeds, herbs, sprouts, mushrooms, algae, flowers, seaweeds and no ...
,
urban agriculture
Urban agriculture, urban farming, or urban gardening is the practice of cultivating, processing, and distributing food in or around urban areas. It encompasses a complex and diverse mix of food production activities, including fisheries and f ...
, and
organic farming
Organic farming, also known as ecological farming or biological farming,Labelling, article 30 o''Regulation (EU) 2018/848 of the European Parliament and of the Council of 30 May 2018 on organic production and labelling of organic products and re ...
, reducing dependency on commercial chemical fertilizers.
The benefits of compost include providing nutrients to crops as
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
, acting as a
soil conditioner, increasing the
humus
In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Lati ...
or
humic acid contents of the soil, and introducing beneficial microbes that help to suppress pathogens in the soil and reduce soil-borne diseases.
At the simplest level, composting requires gathering a mix of
'greens' (green waste) and
'browns' (brown waste).
Greens are materials rich in nitrogen such as leaves, grass, and food scraps.
Browns are woody materials rich in carbon, such as stalks, paper, and wood chips.
The materials break down into
humus
In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Lati ...
in a process taking months. Composting can be a multi-step, closely monitored process with measured inputs of water, air, and carbon- and nitrogen-rich materials. The
decomposition
Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is ...
process is aided by shredding the plant matter, adding water, and ensuring proper aeration by regularly turning the mixture in a process using open piles or "
windrows."
Fungi
A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...
,
earthworm
An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. ...
s, and other
detritivores further break up the organic material.
Aerobic bacteria and fungi manage the chemical process by converting the inputs into heat,
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
, and
ammonium
The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternar ...
.
Composting is an important part of waste management, since food and other compostable materials make up about 20% of waste in landfills, and these materials take longer to biodegrade in the landfill. Composting offers an environmentally superior alternative to using organic material for landfill because composting reduces
anaerobic methane emissions, and provides economic and environmental co-benefits. For example, compost can also be used for land and stream reclamation, wetland construction, and landfill cover.
Fundamentals
Composting is an
aerobic method of decomposing organic solid wastes. It can therefore be used to recycle organic material. The process involves decomposing organic material into a humus-like material, known as compost, which is a good
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
for plants.
Composting organisms require four equally important ingredients to work effectively:
*Carbon is needed for energy; the microbial
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
of carbon produces the heat required for other parts of the composting process.
High carbon materials tend to be brown and dry.
*Nitrogen is needed to grow and reproduce more organisms to oxidize the carbon.
High nitrogen materials tend to be green
and wet.
They can also include colourful fruits and vegetables.
*Oxygen is required for oxidizing the carbon, the decomposition process.
Aerobic bacteria need oxygen levels above 5% to perform the processes needed for composting.
*Water is necessary in the right amounts to maintain activity without causing
anaerobic
Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to:
*Adhesive#Anaerobic, Anaerobic ad ...
conditions.
Certain ratios of these materials will allow microorganisms to work at a rate that will heat up the compost pile. Active management of the pile (e.g., turning over the compost heap with a pitchfork) is needed to maintain sufficient oxygen and the right moisture level. The air/water balance is critical to maintaining high temperatures until the materials are broken down.
Composting is most efficient with a
carbon-to-nitrogen ratio of about 25:1.
Hot composting focuses on retaining heat to increase the decomposition rate thus producing compost more quickly. Rapid composting is favored by having a carbon-to-nitrogen ratio of ~30 carbon units or less. Above 30, the substrate is nitrogen starved. Below 15, it is likely to outgas a portion of nitrogen as ammonia.
Nearly all dead plant and animal materials have both carbon and nitrogen in different amounts. Fresh grass clippings have an average ratio of about 15:1 and dry autumn leaves about 50:1 depending upon species.
Composting is an ongoing and dynamic process, adding new sources of carbon and nitrogen consistently as well as active management is important.
Organisms
Organisms can break down organic matter in compost if provided with the correct mixture of water, oxygen, carbon, and nitrogen.
They fall into two broad categories: chemical decomposers which perform chemical processes on the organic waste, and physical decomposers which process the waste into smaller pieces through methods such as grinding, tearing, chewing, and digesting.
Chemical decomposers
*
Bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
– the most abundant and important of all the
microorganism
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s found in compost.
Bacteria process carbon and nitrogen and excrete plant-available nutrients such as nitrogen, phosphorus, and magnesium.
Depending on the phase of composting,
mesophilic
A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, with an optimum growth range from . The optimum growth temperature for these organisms is 37°C. The term is mainly applied to microorganisms. Org ...
or
thermophilic bacteria may be the most prominent.
** Mesophilic bacteria get compost to the thermophilic stage through oxidation of organic material.
Afterwards, they cure it, which makes the fresh compost more bio-available for plants.
** Thermophilic bacteria do not reproduce and are not active between , yet are found throughout soil. They activate once the mesophilic bacteria have begun to breakdown organic matter and increase the temperature to their optimal range.
They have been shown to enter soils via rainwater.
They are present so broadly because of many factors including their spores being resilient. Thermophilic bacteria thrive at higher temperatures, reaching in typical mixes. Large-scale composting operations, such as
windrow composting, may exceed this temperature, potentially killing beneficial soil microorganisms but also
pasteurizing the waste.
**
Actinomycetota
The ''Actinomycetota'' (or ''Actinobacteria'') are a phylum of all gram-positive bacteria. They can be terrestrial or aquatic. They are of great economic importance to humans because agriculture and forests depend on their contributions to soi ...
are needed to break down paper products such as newspaper,
bark
Bark may refer to:
* Bark (botany), an outer layer of a woody plant such as a tree or stick
* Bark (sound), a vocalization of some animals (which is commonly the dog)
Places
* Bark, Germany
* Bark, Warmian-Masurian Voivodeship, Poland
Arts, ...
, etc and other large molecules such as lignin and cellulose that are more difficult to decompose.
The "pleasant earthy smell of compost" is attributed to Actinomycetota.
They make carbon, ammonia, and nitrogen nutrients available to plants.
*
Fungi
A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...
such as
mold and
yeast
Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to consti ...
help break down materials that bacteria cannot, especially cellulose and
lignin
Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...
in woody material.
*
Protozoa
Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histor ...
– contribute to biodegradation of organic matter as well as consuming non-active bacteria, fungi, and micro-organic particulates.
Physical decomposers
*Ants – create nests, making the soil more porous and transporting nutrients to different areas of the compost.
*Beetles – grubs feed on decaying vegetables.
*
Earthworm
An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. ...
s – ingest partly composted material and excrete worm castings,
making nitrogen, calcium, phosphorus, and magnesium available to plants.
The tunnels they create as they move through the compost also increase aeration and drainage.
*Flies – feed on almost all organic material and input bacteria into the compost.
Their population is kept in check by mites and the thermophilic temperatures that are unsuitable for fly larvae.
*Millipedes – break down plant material.
*
Rotifer
The rotifers (, from the Latin , "wheel", and , "bearing"), commonly called wheel animals or wheel animalcules, make up a phylum (Rotifera ) of microscopic and near-microscopic pseudocoelomate animals.
They were first described by Rev. John H ...
s – feed on plant particles.
*Snails and slugs – feed on living or fresh plant material.
They should be removed from compost before use as they can damage plants and crops.
*Sow bugs – feed on rotting wood, and decaying vegetation.
*Springtails – feed on fungi, mold, and decomposing plants.
Phases of composting
Under ideal conditions, composting proceeds through three major phases:
#Mesophilic phase: an initial, mesophilic phase, in which the decomposition is carried out under moderate temperatures by mesophilic microorganisms.
#Thermophilic phase: as the temperature rises, a second, thermophilic phase starts, in which various thermophilic bacteria carry out the decomposition under higher temperatures (.)
#Maturation phase: as the supply of high-energy compounds dwindles, the temperature starts to decrease, and the mesophilic bacteria once again predominate in the maturation phase.
Hot and cold composting – impact on timing
The time required to compost material relates to the volume of material, the particle size of the inputs (e.g.
wood chips
Woodchips are small- to medium-sized pieces of wood formed by cutting or chipping larger pieces of wood such as trees, branches, logging residues, stumps, roots, and wood waste.
Woodchips may be used as a biomass solid fuel and are raw mater ...
break down faster than branches), and the amount of mixing and aeration.
Generally, larger piles will reach higher temperatures and remain in a thermophilic stage for days or weeks. This is hot composting and is the usual method for large-scale municipal facilities and agricultural operations.
The 'Berkeley method' produces finished compost in eighteen days. It requires assembly of at least of material at the outset and needs turning every two days after an initial four-day phase. Such short processes involve some changes to traditional methods, including smaller, more homogenized particle sizes in the input materials, controlling carbon-to-nitrogen ratio (C:N) at 30:1 or less, and careful monitoring of the moisture level.
Cold composting is a slower process that can take up to a year to complete. It results from smaller piles, including many residential compost piles that receive small amounts of kitchen and garden waste over extended periods. Piles smaller than tend not to reach and maintain high temperatures. Turning is not necessary with cold composting, although there is a risk that parts of the pile may go anaerobic as they become compacted or water-logged.
Pathogen removal
Composting can destroy some
pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...
s and
seed
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosper ...
s, by reaching temperatures above .
Dealing with stabilized compost – i.e. composted material in which microorganisms have finished digesting the organic matter and the temperature has reached between – poses very little risk, as these temperatures kill pathogens and even make
oocysts unviable.
The temperature at which a pathogen dies depends on the pathogen, how long the temperature is maintained (seconds to weeks), and pH.
Compost products like compost tea and compost extracts have been found to have an inhibitory effect on ''
Fusarium oxysporum
''Fusarium oxysporum'' (Schlecht as emended by Snyder and Hansen), an ascomycete fungus, comprises all the species, varieties and forms recognized by Wollenweber and Reinking within an infrageneric grouping called section Elegans. It is part of ...
'',
''Rhizoctonia'' sp., and ''
Pythium debaryanum,'' plant pathogens that can cause crop diseases.
Aerated compost teas are more effective than compost extracts.
The
microbiota and enzymes present in compost extracts also have a suppressive effect on fungal plant pathogens. Compost is a good source of
biocontrol agents like
''B. subtilis'', ''B. licheniformis,'' and P. ''chrysogenum'' that fight plant pathogens.
Sterilizing the compost, compost tea, or compost extracts reduces the effect of pathogen suppression.
Diseases that can be contracted from handling compost
When turning compost that has not gone through phases where temperatures above are reached, a mouth mask and gloves must be worn to protect from diseases that can be contracted from handling compost, including:
*
Aspergillosis
Aspergillosis is a fungal infection of usually the lungs, caused by the genus '' Aspergillus'', a common mould that is breathed in frequently from the air around, but does not usually affect most people. It generally occurs in people with lung di ...
*
Farmer's lung
*
Histoplasmosis – a fungus that grows in guano and bird droppings
*
Legionnaires' disease
Legionnaires' disease is a form of atypical pneumonia caused by any species of '' Legionella'' bacteria, quite often '' Legionella pneumophila''. Signs and symptoms include cough, shortness of breath, high fever, muscle pains, and headaches. ...
*
Paronychia – via infection around the fingernails and toenails
*
Tetanus
Tetanus, also known as lockjaw, is a bacterial infection caused by '' Clostridium tetani'', and is characterized by muscle spasms. In the most common type, the spasms begin in the jaw and then progress to the rest of the body. Each spasm usuall ...
– a central nervous system disease
Oocyte
An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The femal ...
s are rendered unviable by temperatures over .
Environmental Benefits
Composting at home reduces the amount of green waste being hauled to dumps or composting facilities. The reduced volume of materials being picked up by trucks results in less trips which in turn lowers the overall emissions from the waste management fleet.
Materials that can be composted
Potential sources of compostable materials, or feedstocks, include residential, agricultural, and commercial waste streams. Residential food or yard waste can be composted at home, or collected for inclusion in a large-scale municipal composting facility. In some regions, it could also be included in a local or neighborhood composting project.
Organic solid waste
There are two broad categories of organic solid waste: green waste and brown waste.
Green waste is generally considered a source of nitrogen and includes pre and post-consumer
food waste, grass clippings, garden trimmings, and fresh leaves.
Animal carcasses, roadkill, and butcher residue can also be composted and these are considered nitrogen sources.
Brown waste is a carbon source. Typical examples are dried vegetation and woody material such as fallen leaves, straw, woodchips, limbs, logs, pine needles, sawdust, and wood ash but not charcoal ash.
Products derived from wood such as paper and plain cardboard are also considered carbon sources.
Animal manure and bedding
On many farms, the basic composting ingredients are animal
manure
Manure is organic matter that is used as organic fertilizer in agriculture. Most manure consists of animal feces; other sources include compost and green manure. Manures contribute to the fertility of soil by adding organic matter and nut ...
generated on the farm as a
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seve ...
source, and bedding as the carbon source. Straw and sawdust are common bedding materials. Non-traditional bedding materials are also used, including newspaper and chopped cardboard.
The amount of manure composted on a livestock farm is often determined by cleaning schedules, land availability, and weather conditions. Each type of manure has its own physical, chemical, and biological characteristics. Cattle and horse manures, when mixed with bedding, possess good qualities for composting. Swine manure, which is very wet and usually not mixed with bedding material, must be mixed with straw or similar raw materials. Poultry manure must be blended with high-carbon, low-nitrogen materials.
Human excreta
Human excreta, sometimes called "humanure" in the composting context, can be added as an input to the composting process since it is a nitrogen-rich organic material. It can be either composted directly in
composting toilets, or indirectly in the form of
sewage sludge
Sewage sludge is the residual, semi-solid material that is produced as a by-product during sewage treatment of industrial or municipal wastewater. The term " septage" also refers to sludge from simple wastewater treatment but is connected to si ...
after it has undergone treatment in a
sewage treatment plant. Both processes require capable design as there are potential health risks that need to be managed. In the case of home composting, a wide range of microorganisms including bacteria, viruses and parasitic worms can be present in feces, and improper processing can pose significant health risks. In the case of large sewage treatment facilities that collect wastewater from a range of residential, commercial and industrial sources, there are additional considerations. The composted sewage sludge, referred to as
biosolids, can be contaminated with a variety of metals and pharmaceutical compounds. Insufficient processing of biosolids can also lead to problems when the material is applied to land.
Urine
Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra.
Cellular ...
can be put on compost piles or directly used as fertilizer. Adding urine to compost can increase temperatures and therefore increase its ability to destroy pathogens and unwanted seeds. Unlike feces, urine does not attract disease-spreading flies (such as
houseflies
The housefly (''Musca domestica'') is a fly of the suborder Cyclorrhapha. It is believed to have evolved in the Cenozoic Era, possibly in the Middle East, and has spread all over the world as a commensal of humans. It is the most common ...
or
blowflies), and it does not contain the most hardy of pathogens, such as
parasitic worm eggs.
Animal remains
Animal carcasses may be composted as a disposal option. Such material is rich in nitrogen.
Human body
Composting, or formally "natural organic reduction", is an emerging approach to the environmentally-friendly
disposal of human corpses
Disposal of human corpses, also called final disposition, is the practice and process of dealing with the remains of a deceased human being. Disposal methods may need to account for the fact that soft tissue will decompose relatively rapidly, ...
. Mixed with wood chips and aerated, a human corpse turns into compost in a month. The idea is growing in popularity, particularly in the United States where a number of states have either legalized the process or are in the process of doing so.
On September 9th, 2022, California governor Gavin Newsom signed a bill that would allow human composting in California. Burial, cremation and alkaline hydrolysis were the only choices of death care, but with the new bill signed into action, human composting, or natural organic reduction, will be an additional option for “individuals who want a different method to honor their remains after death.” The bill is set to take effect in 2027.
Composting technologies
Industrial-scale
In-vessel composting
Aerated static pile composting
Windrow composting
Other systems at household level
Hügelkultur (raised garden beds or mounds)
The practice of making raised garden beds or mounds filled with rotting wood is also called in German.
It is in effect creating a
nurse log that is covered with soil.
Benefits of garden beds include water retention and warming of soil.
Buried wood acts like a
sponge
Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate throug ...
as it decomposes, able to capture water and store it for later use by crops planted on top of the bed.
Composting toilets
Related technologies
*
Vermicompost
Vermicompost (vermi-compost) is the product of the decomposition process using various species of worms, usually red wigglers, white worms, and other earthworms, to create a mixture of decomposing vegetable or food waste, bedding materials, and ...
(also called
worm castings, worm humus, worm manure, or worm faeces) is the end-product of the breakdown of
organic matter
Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
by earthworms.
These castings have been shown to contain reduced levels of contaminants and a higher saturation of nutrients than the organic materials before vermicomposting.
*
Black soldier fly (''Hermetia illucens'') larvae are able to rapidly consume large amounts of organic material and can be used to treat human waste. The resulting compost still contains nutrients and can be used for
biogas
Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. I ...
production, or further traditional composting or vermicomposting
*
Bokashi is a fermentation process rather than a decomposition process, and so retains the feedstock's energy, nutrient and carbon contents. There must be sufficient carbohydrate for fermentation to complete and therefore the process is typically applied to food waste, including non-compostable items. Carbohydrate is transformed into lactic acid, which dissociates naturally to form lactate, a biological energy carrier. The preserved result is therefore readily consumed by soil microbes and from there by the entire soil food web, leading to a significant increase in soil organic carbon and turbation. The process completes in weeks and returns soil acidity to normal.
* Co-composting is a technique that processes organic solid waste together with other input materials such as dewatered
fecal sludge or
sewage sludge
Sewage sludge is the residual, semi-solid material that is produced as a by-product during sewage treatment of industrial or municipal wastewater. The term " septage" also refers to sludge from simple wastewater treatment but is connected to si ...
.
*
Anaerobic digestion
Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the ferm ...
combined with mechanical sorting of mixed waste streams is increasingly being used in developed countries due to regulations controlling the amount of organic matter allowed in landfills. Treating
biodegradable waste before it enters a landfill reduces
global warming
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate variability and change, Climate change in a broader sense also includes ...
from fugitive
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ear ...
; untreated waste breaks down anaerobically in a landfill, producing
landfill gas that contains methane, a potent
greenhouse gas
A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxide (), met ...
. The methane produced in an anaerobic digester can be converted to
biogas
Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. I ...
.
Uses
Agriculture and gardening
On open ground for growing
wheat
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeolog ...
,
corn
Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn ( North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. ...
,
soybean
The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses.
Traditional unfermented food uses of soybeans include soy milk, from which tofu ...
s, and similar crops, compost can be broadcast across the top of the soil using spreader trucks or spreaders pulled behind a tractor. It is expected that the spread layer is very thin (approximately ) and worked into the soil prior to planting. Application rates of or more are not unusual when trying to rebuild poor soils or control erosion. Due to the extremely high cost of compost per unit of nutrients in the United States, on-farm use is relatively rare since rates over 4 tons/acre may not be affordable. This results from an over-emphasis on "recycling organic matter" than on "sustainable nutrients." In countries such as Germany, where compost distribution and spreading are partially subsidized in the original waste fees, compost is used more frequently on open ground on the premise of nutrient "sustainability".
In
plasticulture,
strawberries
The garden strawberry (or simply strawberry; ''Fragaria × ananassa'') is a widely grown Hybrid (biology), hybrid species of the genus ''Fragaria'', collectively known as the strawberries, which are cultivated worldwide for their fruit. The f ...
,
tomato
The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word , ...
es,
pepper
Pepper or peppers may refer to:
Food and spice
* Piperaceae or the pepper family, a large family of flowering plant
** Black pepper
* ''Capsicum'' or pepper, a genus of flowering plants in the nightshade family Solanaceae
** Bell pepper
** Chili ...
s,
melon
A melon is any of various plants of the family Cucurbitaceae with sweet, edible, and fleshy fruit. The word "melon" can refer to either the plant or specifically to the fruit. Botanically, a melon is a kind of berry, specifically a " pepo". The ...
s, and other fruits and vegetables are grown under plastic to control temperature, retain moisture and control weeds. Compost may be banded (applied in strips along rows) and worked into the soil prior to bedding and planting, be applied at the same time the beds are constructed and plastic laid down, or used as a top dressing.
Many crops are not seeded directly in the field but are started in seed trays in a greenhouse. When the seedlings reach a certain stage of growth, they are
transplanted in the field. Compost may be part of the mix used to grow the seedlings, but is not normally used as the only planting substrate. The particular crop and the seeds' sensitivity to nutrients, salts, etc. dictates the ratio of the blend, and maturity is important to insure that oxygen deprivation will not occur or that no lingering phyto-toxins remain.
Compost can be added to soil,
coir, or
peat
Peat (), also known as turf (), is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. The peatland ecosystem covers and is the most efficien ...
, as a
tilth improver, supplying humus and nutrients.
It provides a rich growing medium as absorbent material. This material contains moisture and soluble minerals, which provide support and
nutrient
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excr ...
s. Although it is rarely used alone, plants can flourish from mixed
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...
,
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a soil texture, textur ...
, grit, bark chips,
vermiculite
Vermiculite is a hydrous phyllosilicate mineral which undergoes significant expansion when heated. Exfoliation occurs when the mineral is heated sufficiently, and commercial furnaces can routinely produce this effect. Vermiculite forms by the we ...
,
perlite, or
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay part ...
granules to produce
loam
Loam (in geology and soil science) is soil composed mostly of sand ( particle size > ), silt (particle size > ), and a smaller amount of clay (particle size < ). By weight, its mineral composition is about 40–40–20% concentration of sand–si ...
. Compost can be tilled directly into the soil or growing medium to boost the level of organic matter and the overall fertility of the soil. Compost that is ready to be used as an additive is dark brown or even black with an earthy smell.
Generally, direct seeding into a compost is not recommended due to the speed with which it may dry, the possible presence of
phytotoxins in immature compost that may inhibit germination, and the possible tie up of nitrogen by incompletely decomposed lignin.
It is very common to see blends of 20–30% compost used for transplanting
seedlings.
Compost can be used to increase plant immunity to diseases and pests.
Compost tea
Compost tea is made up of extracts of fermented water leached from composted materials.
Composts can be either aerated or non-aerated depending on its
fermentation process.
Compost teas are generally produced from adding compost to water in a ratio of 1:4–1:10, occasionally stirring to release
microbes.
There is debate about the benefits of aerating the mixture.
Non-aerated compost tea is cheaper and less labor intensive, but there are conflicting studies regarding the risks of
phytotoxicity
Phytotoxicity describes any adverse effects on plant growth, physiology, or metabolism caused by a chemical substance, such as high levels of fertilizers, herbicides, heavy metals, or nanoparticles. General phytotoxic effects include altered plan ...
and human pathogen regrowth.
Aerated compost tea brews faster and generates more microbes, but has potential for human pathogen regrowth.
Field studies have shown the benefits of adding compost teas to crops due to organic matter input, increased nutrient availability, and increased microbial activity.
They have also been shown to have a suppressive effect on plant pathogens and soil-borne diseases.
The efficacy is influenced by a number of factors, such as the preparation process, the type of source the conditions of the brewing process, and the environment of the crops.
Adding nutrients to compost tea can be beneficial for disease suppression, although it can trigger the regrowth of human pathogens like ''
E. coli'' and ''
Salmonella.''
Compost extract
Compost extracts are unfermented or non-brewed extracts of leached compost contents dissolved in any solvent.
Commercial sale
Compost is sold as bagged potting mixes in garden centers and other outlets.
This may include composted materials such as manure and peat but is also likely to contain loam, fertilizers, sand, grit, etc. Varieties include multi-purpose composts designed for most aspects of planting,
John Innes formulations,
grow bags, designed to have crops such as tomatoes directly planted into them. There are also a range of specialist composts available, e.g. for vegetables, orchids, houseplants, hanging baskets, roses, ericaceous plants, seedlings, potting on, etc.
Other
Compost can also be used for land and stream reclamation,
wetland construction, and
landfill cover.
The temperatures generated by compost can be used to heat
greenhouse
A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of transparent material, such as glass, in which plants requiring regulated climatic conditions are grown.These ...
s, such as by being placed around the outside edges.
Regulations
There are process and product guidelines in Europe that date to the early 1980s (Germany, the Netherlands, Switzerland) and only more recently in the UK and the US. In both these countries, private trade associations within the industry have established loose standards, some say as a stop-gap measure to discourage independent government agencies from establishing tougher consumer-friendly standards. Compost is regulated in Canada and Australia as well.
EPA Class A and B guidelines in the United States were developed solely to manage the processing and
beneficial reuse of
sludge, also now called
biosolids, following the US EPA ban of ocean dumping. About 26 American states now require composts to be processed according to these federal protocols for
pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...
and
vector control, even though the application to non-sludge materials has not been scientifically tested. An example is that green waste composts are used at much higher rates than sludge composts were ever anticipated to be applied at. U.K guidelines also exist regarding compost quality, as well as Canadian, Australian, and the various European states.
In the United States, some compost manufacturers participate in a testing program offered by a private lobbying organization called the U.S. Composting Council. The USCC was originally established in 1991 by Procter & Gamble to promote composting of disposable diapers, following state mandates to ban diapers in landfills, which caused a national uproar. Ultimately the idea of composting diapers was abandoned, partly since it was not proven scientifically to be possible, and mostly because the concept was a marketing stunt in the first place. After this, composting emphasis shifted back to recycling organic wastes previously destined for landfills. There are no bonafide quality standards in America, but the USCC sells a seal called "Seal of Testing Assurance" (also called "STA"). For a considerable fee, the applicant may display the USCC logo on products, agreeing to volunteer to customers a current laboratory analysis that includes parameters such as nutrients, respiration rate, salt content, pH, and limited other indicators.
Many countries such as
Wales
Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...
and some individual cities such as Seattle and
San Francisco
San Francisco (; Spanish language, Spanish for "Francis of Assisi, Saint Francis"), officially the City and County of San Francisco, is the commercial, financial, and cultural center of Northern California. The city proper is the List of Ca ...
require food and yard waste to be sorted for composting (
San Francisco Mandatory Recycling and Composting Ordinance The San Francisco Mandatory Recycling and Composting Ordinance (No. 100-09) is a local municipal ordinance requiring all persons located in San Francisco to separate their recyclables, compostables and landfilled trash and to participate in recyclin ...
).
The USA is the only Western country that does not distinguish sludge-source compost from green-composts, and by default 50% of US states expect composts to comply in some manner with the federal EPA 503 rule promulgated in 1984 for sludge products.
There are health risk concerns about
PFASs
Per- and polyfluoroalkyl substances (PFASs) are synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain. An early definition, from 2011, required that they contain at least one perfluoroalkyl mo ...
("forever chemicals") levels in compost derived from sewage sledge sourced biosolids, and
EPA
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
has not set health risk standards for this. The
Sierra Club
The Sierra Club is an environmental organization with chapters in all 50 United States, Washington D.C., and Puerto Rico. The club was founded on May 28, 1892, in San Francisco, California, by Scottish-American preservationist John Muir, w ...
recommends that home gardeners avoid the use of sewage sludge-base fertilizer and compost, in part due to potentially high levels of PFASs. The EPA PFAS Strategic Roadmap initiative, running from 2021 to 2024, will consider the full lifecycle of PFAS including health risks of PFAS in wastewater sludge.
History
Composting dates back to at least the early Roman Empire, and was mentioned as early as
Cato the Elder
Marcus Porcius Cato (; 234–149 BC), also known as Cato the Censor ( la, Censorius), the Elder and the Wise, was a Roman soldier, Roman Senate, senator, and Roman historiography, historian known for his conservatism and opposition to Hellenizati ...
's 160 BCE piece . Traditionally, composting involved piling organic materials until the next planting season, at which time the materials would have decayed enough to be ready for use in the soil. The advantage of this method is that little working time or effort is required from the composter and it fits in naturally with agricultural practices in temperate climates. Disadvantages (from the modern perspective) are that space is used for a whole year, some nutrients might be leached due to exposure to rainfall, and disease-producing organisms and insects may not be adequately controlled.
Composting began to modernize somewhat from the 1920s in Europe as a tool for
organic farming
Organic farming, also known as ecological farming or biological farming,Labelling, article 30 o''Regulation (EU) 2018/848 of the European Parliament and of the Council of 30 May 2018 on organic production and labelling of organic products and re ...
.
The first industrial station for the transformation of urban organic materials into compost was set up in
Wels, Austria in the year 1921. Early proponents of composting within farming include
Rudolf Steiner
Rudolf Joseph Lorenz Steiner (27 or 25 February 1861 – 30 March 1925) was an Austrian occultist, social reformer, architect, esotericist, and claimed clairvoyant. Steiner gained initial recognition at the end of the nineteenth century as ...
, founder of a farming method called
biodynamics, and
Annie Francé-Harrar
Annie Francé-Harrar (born 2 December 1886 Munich, Germany; died 23 January 1971 Hallein, Austria) was an Austrian writer and scientist.
Francé-Harrar created the scientific basis for the humus-compost-economy mperfect literal translation from ...
, who was appointed on behalf of the government in
Mexico
Mexico ( Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guate ...
and supported the country in 1950–1958 to set up a large humus organization in the fight against erosion and
soil degradation
Soil retrogression and degradation are two regressive evolution processes associated with the loss of equilibrium of a stable soil. Retrogression is primarily due to soil erosion and corresponds to a phenomenon where succession reverts the land t ...
.
Sir Albert Howard, who worked extensively in
India
India, officially the Republic of India ( Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the ...
on sustainable practices,
and
Lady Eve Balfour were also major proponents of composting. Composting was imported to America by the likes of:
*
J. I. Rodale – founder of
Rodale, Inc. Organic Gardening
*
Paul Keene – founder of Walnut Acres in Pennsylvania
* and
Scott
Scott may refer to:
Places Canada
* Scott, Quebec, municipality in the Nouvelle-Beauce regional municipality in Quebec
* Scott, Saskatchewan, a town in the Rural Municipality of Tramping Lake No. 380
* Rural Municipality of Scott No. 98, Saska ...
and
Helen Nearing – inspired the
back-to-the-land movement of the 1960s
See also
*
Carbon farming
Carbon farming is a name for a variety of agricultural methods aimed at sequestering atmospheric carbon into the soil and in crop roots, wood and leaves. The aim of carbon farming is to increase the rate at which carbon is sequestered into soil a ...
*
Human composting
*
Organic farming
Organic farming, also known as ecological farming or biological farming,Labelling, article 30 o''Regulation (EU) 2018/848 of the European Parliament and of the Council of 30 May 2018 on organic production and labelling of organic products and re ...
*
Permaculture
*
Soil science
Soil science is the study of soil as a natural resource on the surface of the Earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to ...
*
Sustainable agriculture
*
Terra preta
''Terra preta'' (, locally , literally "black soil" in Portuguese) is a type of very dark, fertile anthropogenic soil ( anthrosol) found in the Amazon Basin. It is also known as "Amazonian dark earth" or "Indian black earth". In Portuguese its ...
*
Waste sorting
*
Zero waste
Zero waste is a set of principles focused on waste prevention that encourages redesigning resource life cycles so that all products are reused. The goal of this movement is to avoid sending trash to landfills, incinerators, or the ocean. Cur ...
Related lists
*
List of composting systems
*
List of environment topics
*
List of sustainable agriculture topics
The following outline is provided as an overview of and topical guide to sustainable agriculture:
Sustainable agriculture – applied science that integrates three main goals, environmental health, economic profitability, and social and econ ...
*
List of organic gardening and farming topics
The following outline is provided as an overview of and topical guide to organic gardening and farming:
Organic farming – alternative agricultural system that relies on fertilizers of organic origin such as compost, manure, green manure ...
References
{{Authority control
Organic fertilizers
Waste management
Gardening aids
Sanitation
Soil improvers
Soil
Sustainable food system
Biodegradable waste management
Permaculture