Composting

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From Wikipedia:

Compost is organic matter that has been decomposed and recycled as a fertilizer and soil amendment. At the simplest level, the process of composting simply requires making a heap of wetted organic matter known as green waste (leaves, food waste) and waiting for the materials to break down into humus after a period of weeks or months. 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.

As plants grow, they extract nutrients from the soil. Composting is a way to cycle the nutrient back to the soil.

To maintain the soil furtile, techniques such as crop intermixing and crop rotation are used. When the compost is built using a rich variety of organic material, composting is another way of 'crop mixing' to avoid that the soil becomes depleted in nutrients and to provide a rich mix of microorganisms to assure soil biodiversity.

Carbon to nitrogen ratio

Copied from [1]:

Of the many elements required for microbial decomposition, carbon and nitrogen are the most important. Carbon provides both an energy source and and the basic building block making up about 50 percent of the mass of microbial cells. Nitrogen is a crucial component of the proteins, nucleic acids, amino acids, enzymes and co-enzymes necessary for cell growth and function.

To provide optimal amounts of these two crucial elements, you can use the carbon-to-nitrogen (C/N) ratio for each of your compost ingredients. The ideal C/N ratio for composting is generally considered to be around 30:1, or 30 parts carbon for each part nitrogen by weight. Why 30:1? At lower ratios, nitrogen will be supplied in excess and will be lost as ammonia gas, causing undesirable odors. Higher ratios mean that there is not sufficient nitrogen for optimal growth of the microbial populations, so the compost will remain relatively cool and degradation will proceed at a slow rate.

Typical C/N ratios for common compost materials can be looked up in published tables such as Appendix A, On-Farm Composting Handbook. In general, materials that are green and moist tend to be high in nitrogen, and those that are brown and dry are high in carbon. High nitrogen materials include grass clippings, plant cuttings, and fruit and vegetable scraps. Brown or woody materials such as autumn leaves, wood chips, sawdust, and shredded paper are high in carbon.


Techniques

Forest ground cover

Composting takes place naturally in forests when microorganisms process the layer of falling leaves on the ground.

Sheet composting

Not to be confused with the more evolved technique of sheet mulching.

Sheet composting is inspired by the natural occuring composting process in forests. Green wastes (leaves and other) are spread out on the soil surface. See also [2]. Some people dig the uncomposted organic materials into the soil.

Positive:

  • Easy

Negative:

  • According to Jeavons: The disadvantage of this method is that the soil should not be planted for 3 onths until decomposition has occurred. Soil bacteria tie up the nitrogen during the decomposition process thereby making it unavailable to the plants. Sheet composting may be beneficial during the winter in cold areas. (Jeavons p.56) The effect of tying up the nitrogen may may significant only if the organic matter is dug into the soil, or when a large amount of organic matter is added at once. [MORE REFS?]
  • Kitchen wastes on the soil surface is not aesthetic.

Vermicompost

From Wikipedia:
Vermicompost is the product or process of composting using various worms, usually red wigglers, white worms, and other earthworms to create a heterogeneous mixture of decomposing vegetable or food waste, bedding materials, and vermicast. Vermicast, also called worm castings, worm humus or worm manure, is the end-product of the breakdown of organic matter by an earthworm. These castings have been shown to contain reduced levels of contaminants and a higher saturation of nutrients than do organic materials before vermicomposting.

Positive:

  • Can be done inside the house.
  • Doesn't take up much space.

Cold compost pile

Summary: pile organic materials and let them stand for a year.

Hot compost pile

Also called The Berkley Rapid Composting Method (Raabe,R.D. 2001 The Rapid Composting Method. Co-operative Extension, Division of Agriculture and Natural Resources, University of California).


  • The compost pile has to be around one cubic meter in size.
  • The whole pile is made at once.
  • Equal parts green and brown materials, all shredded to a small size.
  • Add some soil or mature compost.
  • Maintain the pile humid but not soaking wet.

Positive:

  • Fast decomposition process.
  • Kills of some/most/all (see notes below) weed seeds or disease pathogens

Negative:

  • The pile has to be built on soil. Can't be done inside the house or on a balcony.
  • Requires planning to have all the materials available at once (where do you store mature materials and avoid that they start composting?).
  • May require a shredder (costly/noisy/energy-guzzling).

Adding soil: Some peopla recommend to add soil to the compost pile. Some don't. Here are some arguments:

  • For: Soil enables the pile to hold moisture better--facilitating the decomposition of the pile (Jeavons p. 48).
  • For: The soil holds many of the nutrient-laden compost "juices", keeping them from leaching out (Jeavons p. 48).
  • For: Soil contains a good strater supply of microorganisms that enable the pile to decompose more easily (Jeavons p. 48/49).
  • For: Soil contains bacteria of a type that helps stabilize nitrogen in a pile. An excessive concentration of available nitrogen in the soil (which makes plants susceptible to disease) is therefore avoided (Jeavons p. 48).
  • For: Soil contains predaceous fungi that attack and devour nematodes but these fungi are only found in large amount in a soil with adequate humus (Jeavons p. 48).
  • Against: Soil adds nothing but weight to a compost pile and will discourage the turning of the pile which is necessary for the rapid composting process (Robert D. Raabe, The Rapid Composting Method [3]).

Notes:

  • According to Jeavons (Jeavons p. 61), most hot compost piles cure around 60°C (139°F). At this temperature, probably only 25% of the weed seeds, disease organisms, and insect larvae are destroyed. It takes temperatures of 81°C (178°F) to kill 100% of them. This temperature burns off a lot of the organic matter that could become cured compost.

See also:

GROW BIOINSTENSIVE

  • Minimum compost pile size of 90cmx90cm (3 feet x 3 feet)
  • Best time to prepare compost is in spring or autumn.

Recipe 1

The first recipe is a variation of the hot compost pile. It uses 45% volume of mature, dry material, 45% volune of immature, green vegetation, and 10% volume of soil.

  1. Under the pile area, loosen the soil to 30cm (12 inches) deep with a spading fork.
  2. Lay down 10cm (3") of roughage (brush, woody material) for air circulation.
  3. Put down 5cm (2") of mature material (dry weeds, leaves, straw, hay, old garden wastes). Water it thoroughly.
  4. Put down 5cm (2") of immature material (fresh weeds, grass clipping, hedge trimmings, green cover crops, kitchen wastes). Water it well.
  5. Cover lightly with a layer of soil 1 to 2 cm thick (1/4" - 1/2").
  6. Moisten the soil.
  7. Add new layers of mature vegetation, immature vegetation, and soil.
  8. Cover the top of the pile with 1 to 2.5 cm of soil.
  9. Water the completed pile regularly until it is ready for use.
  10. Let the completed pile cure for 3 to 6 months. Turn the pile once for faster decomposition (after three weeks, after the temperature of the pile has peaked and fallen (p.54)).

Ref: (Jeavons p. 59)

Sheet mulching

See also [4].

Green manure

Grow cover crops (vetch, clover, alfalfa, beans, peas, other legumes) until the plants are at 10% to 50% flower. The nitrogen-rich plants are then dug into the soil.

Positive:

  • Provides nitrogen
  • Helps loosen soil
  • Root turn into humus

Negative:

  • According to Jeavons: We find that green-manure crops are more effective when used as compost materials: 1. Due to their high nitrogen contents they decompose rapidly when dug into the soil and may deplete some of the soil's humus. 2. The land is not producing food crops during the period of the cover crop growth and the 1-month period of decomposition. 3. Green manures only produce only about one quarter the carbon in a given area that carbonaceous compost crops do, and carbon in the form of humus is the most limiting and essential element in maintaining sustainable soil furtility. (Jeavons p.56)

Locating the compost pile

  • Option 1: Under an oak tree (Jeavons, p.49)
  • Option 2: Under any other deciduous tree (except walnut and eucalyptus) (Jeavons, p.50)
  • Option 3: In a shady place in your backyard (Jeavons, p.50)


See also

References

  • FAO, ON-FARM COMPOSTING METHODS [5]
  • Raabe,R.D. 2001 The Rapid Composting Method. Co-operative Extension, Division of Agriculture and Natural Resources, University of California [6].
  • On-Farm Composting Handbook, NRAES (Natural Resource, Agriculture, and Engineering Service) [7] and [8].