Compost (pronounced
/ˈkɒmpɒst/ or
/ˈkɒmpoʊst/) is plant matter that has been
decomposed and recycled as a fertilizer and soil amendment. Compost is a key ingredient in
organic farming. At its most essential, the process of
composting requires simply piling up waste outdoors and waiting a year or more. Modern, methodical composting is a multi-step, 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. Worms and fungi further break up the material.
Aerobic bacteria manage the chemical process by converting the inputs into heat, carbon dioxide and ammonium. The ammonium is further refined by bacteria into plant-nourishing nitrites and nitrates.
Compost can be rich in nutrients. It is used in
gardens,
landscaping,
horticulture, and
agriculture. The compost itself is beneficial for the land in many ways, including as a
soil conditioner, a
fertilizer, addition of vital
humus or
humic acids, and as a natural
pesticide for soil. In ecosystems, compost is useful for erosion control, land and stream reclamation, wetland construction, and as landfill cover (see
compost uses).
History
A modern compost bin constructed from plastic.
Composting as a recognized practice dates to at least the early Roman Empire since
Pliny the Elder (AD 23-79). Traditionally, composting was to pile 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, some weed, weed seeds and insects may not be adequately controlled.
Composting was somewhat modernized beginning in the 1920s in Europe as a tool for
organic farming.
[1] The first industrial station for the transformation of urban organic materials into compost was set up in Wels/Austria in the year 1921.
[2] The early personages most cited for propounding composting within farming are for the German-speaking world
Rudolf Steiner, founder of a farming method called
biodynamics, and
Annie Francé-Harrar, who was appointed on behalf of the government in
Mexico and supported the country 1950–1958 to set up a large humus organization in the fight against erosion and soil degradation. In the English-speaking world it was
Sir Albert Howard who worked extensively in
India on sustainable practices and
Lady Eve Balfour who was a huge proponent of composting. Composting was imported to America by various followers of these early European movements in the form of persons such as
J.I. Rodale (founder of Rodale Organic Gardening), E.E. Pfeiffer (who developed scientific practices in biodynamic farming), Paul Keene (founder of Walnut Acres in Pennsylvania), and Scott and Helen Nearing (who inspired the back-to-land movement of the 1960s). Coincidentally, some of these personages met briefly in India - all were quite influential in the U.S. from the 1960s into the 1980s.
There are many modern proponents of rapid composting which attempt to correct some of the perceived problems associated with traditional, slow composting. Many advocate that compost can be made in 2 to 3 weeks.
[3] Many such short processes involve a few changes to traditional methods, including smaller, more homogenized pieces in the compost, controlling
carbon to nitrogen (CN) ratio at 30 to 1 or less, and monitoring the moisture level more carefully. However, none of these parameters differ significantly from early writings of Howard and Balfour, suggesting that in fact modern composting has not made significant advances over the traditional methods which take a few months to work. For this reason and others, many modern scientists who deal with carbon transformations are sceptical that there is a "super-charged" way to get nature to make compost rapidly.
[citation needed] They also point to the fact that it is the structure of the natural molecules - such as
carbohydrates,
proteins, and
cellulose - that really dictate the rate at which microbial-mediated transformations are possible.
Some cities such as Seattle and San Francisco require food and yard waste to be sorted for composting.
[4][5]
Ingredients
Home compost barrel in the Escuela Barreales, Chile.
Composting organisms require four equally important things to work effectively:
- Carbon — for energy; the microbial oxidation of carbon produces the heat[citation needed].
- High carbon materials tend to be brown and dry.
- Nitrogen — to grow and reproduce more organisms to oxidize the carbon.
- High nitrogen materials tend to be green (or colorful, such as fruits and vegetables) and wet.[6]
- Oxygen — for oxidizing the carbon, the decomposition process.
- Water — in the right amounts to maintain activity without causing anaerobic conditions.
Materials in a compost pile.
Certain ratios of these materials will provide beneficial bacteria with the nutrients to work at a rate that will heat up the pile. In that process much water will be released as
vapor ("steam"), and the oxygen will be quickly depleted, explaining the need to actively manage the pile. The hotter the pile gets, the more often added air and water is necessary; the air/water balance is critical to maintaining high temperatures until the materials are broken down. At the same time, too much air or water also slows the process, as does too much carbon (or too little nitrogen).
The most efficient composting occurs with a carbon:nitrogen mix of about 30 to 1. Nearly all plant and animal materials have both carbon and nitrogen, but amounts vary widely, with characteristics noted above (dry/wet, brown/green).
[7] Fresh grass clippings have an average ratio of about 15 to 1 and dry autumn leaves about 50 to 1 depending on species. Mixing equal parts by volume approximates the ideal C:N range. Few individual situations will provide the ideal mix of materials at any point in time - in this respect, home composting is like horseshoes, perfect is great, but close still works. Observation of amounts, and consideration of different materials
[8] as a pile is built over time, can quickly achieve a workable technique for the individual situation.
Urine
People excrete far more of certain
water-soluble plant nutrients (
nitrogen,
phosphorus,
potassium) in
urine than in
feces.
[9] Human
urine can be used directly as fertilizer or it can be put onto compost. Adding a healthy person's
urine to compost usually will increase temperatures and therefore increase its ability to destroy pathogens and unwanted seeds. Urine from a person with no obvious symptoms of infection is generally much more sanitary than fresh
feces. Unlike feces, urine doesn't attract disease-spreading
flies (such as
house flies or
blow flies), and it doesn't harbor the most hardy of pathogens, such as
parasitic worm eggs. Urine usually does not
stink for long, particularly when it is fresh, diluted, or put on
sorbents.
Urine is primarily composed of water and
urea. Although metabolites of urea are nitrogen fertilizers, it is easy to over-fertilize with urine creating too much ammonia for plants to absorb, acidic conditions, or other
phytotoxicity.
Manure and bedding
On many farms, the basic composting ingredients are manure generated on the farm and bedding. Straw and sawdust are common bedding materials. Nontraditional 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, needs to be mixed with straw or similar raw materials. Poultry manure also needs to be blended with carbonaceous materials - preferably those low in nitrogen, such as sawdust or straw.
[10]
Micro-organisms
With the proper mixture of water, oxygen, carbon, and nitrogen, micro-organisms are allowed to break down organic matter to produce compost.
[11] The composting process is dependant on micro-organisms to break down organic matter into compost. There are many types of microorganisms found in active compost of which the most common are:
[12]
- Bacteria- The most numerous of all the micro organisms found in compost.
- Actinomycetes- Necessary for breaking down paper products such as newspaper, bark, etc.
- Fungi- Molds and yeast help break down materials that bacteria cannot, especially lignin in woody material.
- Protozoa- Help consume bacteria, fungi and micro organic particulates.
- Rotifers- Rotifers help control populations of bacteria and small protozoans.
In addition,
earthworms not only ingest partly composted material, but also continually re-create aeration and drainage tunnels as they move through the compost.
A lack of a healthy micro-organisms community is the main reason why composting processes are slow in
landfills with environmental factors such as lack of oxygen, nutrients or water being the cause of the depleted biological community.
[12]
Common Items Suitable for Composting
You can always add these items to your compost and you are unlikely to negatively affect your composting efforts.
[13]
- Cardboard or clean paper
- Dried Out Egg Shells
- Leaves, Yard Trimmings
- Fruits and Vegetables, Coffee and Tea
Uses
Compost is generally recommended as an additive to soil, or other matrices such as
coir and
peat, as a
tilth improver, supplying
humus and nutrients. It provides a rich
growing medium, or a porous, absorbent material that holds moisture and soluble minerals, providing the support and
nutrients in which plants can flourish, although it is rarely used alone, being primarily mixed with
soil,
sand, grit,
bark chips,
vermiculite,
perlite, or
clay granules to produce
loam.
Generally, direct seeding into a compost is not recommended due to the speed with which it may dry and the possible presence of
phytotoxins which may inhibit germination,
[14][15][16] and the possible tie up of nitrogen by incompletely decomposed
lignin.
[8] It is very common to see blends of 20–30% compost used for transplanting
seedlings at
cotyledon stage or later.
Destroying pathogens, seeds, or unwanted plants
Composting can destroy
pathogens or unwanted
seeds. Unwanted living plants (or
weeds) can be destroyed by
covering with mulch/compost.
The "
microbial pesticides" in compost may include
thermophiles and
mesophiles, however certain composting
detritivores such as
black soldier fly larvae and
redworms, also reduce many pathogens. Thermophilic (high-temperature) composting is well known to destroy many seeds and nearly all types of pathogens (exceptions may include
prions). However, thermophilic composting requires a fair amount of material, around a cubic meter.
The
sanitizing qualities of (
thermophilic) composting are desirable where there is a high likelihood of pathogens, such as with
manure. Applications include
humanure composting or the
deep litter technique.
Types
Compost tea
Compost tea is a liquid solution or suspension made by steeping compost in water. It is used as both a
fertilizer and in attempts to prevent plant diseases.
[17] The liquid is applied as a spray to non-edible plant parts, or as a soil-drench (root dip), such as seedlings, or as a surface spray to reduce incidence of harmful
phytopathogenic fungi in the
phyllosphere.
[18] Compost tea has been shown to cause a 173.5% increase in plant growth by mass over plants grown without castings. These results were seen with only 10% addition of castings to produce these results.
[19]
Vermicompost
Rotary screen harvested worm castings
is the product of
composting utilizing various species of worms, usually
red wigglers,
white worms, and
earthworms to create a heterogeneous mixture of decomposing vegetable or food waste, bedding materials, and vermicast. Vermicast, also known as
worm castings, worm humus or worm manure, is the end-product of the breakdown of
organic matter by
species of
earthworm.
[20]
The earthworm species (or
composting worms) most often used are Red Wigglers (
Eisenia foetida or
Eisenia andrei), though European nightcrawlers (
Eisenia hortensis) could also be used.
Red wigglers are recommended by most vermiculture experts as they have some of the best appetites and breed very quickly. Users refer to European nightcrawlers by a variety of other names, including
dendrobaenas,
dendras, and
Belgian nightcrawlers.
Containing water-soluble nutrients,
vermicompost is a nutrient-rich
organic fertilizer and soil conditioner.
[21]
Bokashi composting
Inside a recently started Bokashi bin. The aerated base is just visible through the food scraps and Bokashi bran.
Bokashi is a method of intensive
composting. It can use an
aerobic or
anaerobic inoculation to produce the compost. Once a
starter culture is made, it can be used to extend the culture indefinitely, like
yogurt culture. Since the popular introduction of
effective microorganisms (EM), Bokashi is commonly made with only
molasses, water, EM, and
wheat bran.
In home composting applications, kitchen waste is placed into a container which can be sealed with an
air tight lid. These scraps are then
inoculated with a Bokashi
EM mix. This usually takes the form of a carrier, such as
rice hulls, wheat bran or saw dust, that has been inoculated with composting micro-organisms. The EM are natural
lactic acid bacteria, yeast, and
phototrophic bacteria that act as a microbe community within the kitchen scraps, fermenting and accelerating breakdown of the organic matter. The user would place alternating layers of food scraps and Bokashi mix until the container is full.
Hügelkultur
The practice of making raised beds filled with rotting wood.
[22][23] It is in effect creating a
Nurse log though covered with dirt. The buried decomposing wood will give off heat, as all compost does, for several years. This effect has been used by
Sepp Holzer for one to allow fruit trees to survive at otherwise inhospitable temperatures and altitudes.
Alternative to landfilling
As concern about
landfill space increases, worldwide interest in
recycling by means of
composting is growing, since composting is a process for converting decomposable organic materials into useful stable products.
[24] Industrial scale composting in the form of
in-vessel composting,
aerated static pile composting, and
anaerobic digestion takes place in most Western countries now, and in many areas is mandated by law. There are process and product guidelines in Europe that date to the early 1980s (Germany, Holland, 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.
[25][26] The USA is the only Western country that does not distinguish sludge-source compost from green-composts, and by default in the USA 50% of states expect composts to comply in some manner with the federal EPA 503 rule promulgated in 1984 for sludge products.
[27] Compost is regulated in Canada and Australia as well.
Industrial systems
A large (and over sized) compost pile that is steaming with the heat generated by thermophilic microorganisms.
Industrial composting systems are increasingly being installed as a waste management alternative to
landfills, along with other
advanced waste processing systems. Mechanical sorting of mixed waste streams combined with
anaerobic digestion or
in-vessel composting, is called
mechanical biological treatment, increasingly 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.
Large-scale composting systems are used by many urban centers around the world. Co-composting is a technique which combines solid waste with de-watered biosolids, although difficulties controlling inert and plastic contamination from
municipal solid waste makes this approach less attractive. The world's largest MSW co-composter is the
Edmonton Composting Facility in
Edmonton,
Alberta,
Canada, which turns 220,000 tonnes of residential solid waste and 22,500 dry tonnes of biosolids per year into 80,000 tonnes of compost. The facility is 38,690 meters
2 (416,500 ft
2), equivalent to 4½
Canadian football fields, and the operating structure is the largest stainless steel building in
North America, the size of 14
NHL rinks.
[28] In 2006, the
State of Qatar awarded Keppel Seghers, a subsidiary of
Keppel Corporation to begin construction on a 275,000 tonne/year Anaerobic Digestion and Composting Plant. This plant, with 15 independent anaerobic digestors will be the World's Largest Composting facility once fully operational in early 2011 and forms part of the
Qatar Domestic Solid Waste Management Center, the largest integrated
waste management complex in the
Middle East.
[29]
