Compost

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 and 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 gardens, landscaping, horticulture, urban agriculture, and organic farming, reducing dependency on commercial chemical fertilizers.^[1] The benefits of compost include providing nutrients to crops as fertilizer, acting as a soil conditioner, increasing the humus or humic acid contents of the soil, and introducing beneficial microbes that help to suppress pathogens in the soil and reduce soil-borne diseases.

"Composting" redirects here. Not to be confused with Compositing.

At the simplest level, composting requires gathering a mix of "greens" (green waste) and "browns" (brown waste).^[1] Greens are materials rich in nitrogen, such as leaves, grass, and food scraps.^[1] Browns are woody materials rich in carbon, such as stalks, paper, and wood chips.^[1] The materials break down into humus in a process taking months.^[2] Composting can be a multistep, closely monitored process with measured inputs of water, air, and carbon- and nitrogen-rich materials. The decomposition 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.^[1]^[3] Fungi, earthworms, 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, and ammonium ions.

Composting is an important part of waste management, since food and other compostable materials make up about 20% of waste in landfills, and due to anaerobic conditions, these materials take longer to biodegrade in the landfill.^[4]^[5] Composting offers an environmentally superior alternative to using organic material for landfill because composting reduces methane emissions due to anaerobic conditions, and provides economic and environmental co-benefits.^[6]^[7] For example, compost can also be used for land and stream reclamation, wetland construction, and landfill cover.

Carbon is needed for energy; the microbial of carbon produces the heat required for other parts of the composting process.^[3] High carbon materials tend to be brown and dry.^[1]^[3]

oxidation

Nitrogen is needed to grow and reproduce more organisms to oxidize the carbon. High nitrogen materials tend to be green^[1] and wet.^[3] They can also include colourful fruits and vegetables.^[1]

[3]

Oxygen is required for oxidizing the carbon, the decomposition process. Aerobic bacteria need oxygen levels above 5% to perform the processes needed for composting.^[3]

[3]

Water is necessary in the right amounts to maintain activity without causing locally conditions.^[1]^[3]

anaerobic

Environmental benefits[edit]

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 fewer trips, which in turn lowers the overall emissions from the waste-management fleet.

(also called worm castings, worm humus, worm manure, or worm faeces) is the end product of the breakdown of organic matter by earthworms.^[59] These castings have been shown to contain reduced levels of contaminants and a higher saturation of nutrients than the organic materials before vermicomposting.^[60]

Vermicompost

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 production, or further traditional composting or vermicomposting^[61]^[62]

Black soldier fly (Hermetia illucens)

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 noncompostable 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.

Bokashi

Co-composting is a technique that processes organic solid waste together with other input materials such as dewatered or sewage sludge.^[10]

fecal sludge

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 from fugitive methane; untreated waste breaks down anaerobically in a landfill, producing landfill gas that contains methane, a potent greenhouse gas. The methane produced in an anaerobic digester can be used as biogas.^[63]