Compost is a biological process where micro-organisms recycle decaying or decomposing organic matter to produce a soil conditioner that can be applied as an additive to improve soil conditions. Composting takes place in the presence of oxygen (aerobic conditions), and with adequate temperature and moisture, transforming organic matter into plant-available nutrients. Compost can comprise organic plant and/or animal matter, and/or residues including leaves, dead roots, manure, urine, bones, and nematodes, amongst other organic materials. As it is generally rich in nutrients, the application of compost can naturally fortify soils, acting as a fertiliser, with soil humus or natural pesticide increasing the resistance of plants to diseases, foreign species and insects. The amount of organic matter in different soils depends on the soil type, vegetation species, and other environmental conditions, such as moisture and temperature. Thus, the application of compost may add important nutrients to soils that can benefit vegetation growth. Rainfall, temperature changes and other biophysical factors may result in a diminishing return of compost benefits to soil health. Therefore, the application of compost to soils should be a continuous practice, in order to increase physical, chemical and biological benefits. There are two main composting systems: Open Systems (compost piles or pits) or Contained Composting – see technical application below. This is a climate smart approach as it recycles readily available organic materials from a farm for use within the farming system, plus it avoids the use of chemical fertilisers. Composting is a climate smart approach as it reduces the need for chemical fertilisers, contributes to soil amendments that support adaptation to climate change, and helps retain soil fertility, which in turn aids agricultural productivity.
To effectively undertake composting:
- Step 1: gather compostable materials - rests of harvests, animal manure and dung, organic kitchen waste (fruit and vegetable waste), other food waste, edible oils and fats, wood shavings, paper products (not printed), hair cut waste. Avoid non-compostable materials such as chemical residues, glass, metals, plastics, carcasses, cooked leftovers or meat.
- Step 2: Chop/cut materials to achieve optimum particle size is between 5 – 20 cm – this will assist decomposition. Wire mesh can be used to sift smaller non-organic particles.
- Step 3: Add water regularly using a watering-can to assist decomposition, ensuring that the materials do not become water logged.
- Step 4: Using a pitchfork or shovel, turn-over or rotate compost materials regularly as oxygen is a key component to the decomposition process.
- Step 5: If available, add earthworms (known as vermiculture) to compostable material, which enriches soil, enhances plant growth (hence yields) and suppresses disease.
- Step 6: Once compost material has been decomposed (three months to two years, depending on climate and composting material) it will be a fine, dark material. Screen the material to remove large particles and mix with soils in gardens or fields prior planting and around plants throughout growing period.
- Step 7: If compost does not include animal manure/waste it can be applied to crops as an organic fertiliser at any point up to harvest. If it does include animal waste, it can be incorporated into soil not less than 120 days prior to harvest, especially where edible portion of crops has been in contact with the soil surface.
Additional notes:
- For Open Composting System (Piles): select a level area or dig a pit with a level bottom away from developed areas, chop collected materials into piles, turn over or rotate and add water to material regularly (weekly or bi-monthly). Cover pile if there is heavy rain to prevent materials from washing away and becoming water-logged.
- For Contained Composting Systems: construct a container unit from mesh, wooden panels, bricks and other suitable building materials, fill the container with chopped material, turn over or rotate, and add water to material regularly (weekly or bi-monthly). Keep compostable material covered.
- US Composting Council 1999. Home Composting: Recycling In Your Own Back-Yard.
- Food and Agriculture Organisation. 2015. Farmer’s Compost Handbook: Experiences in Latin America. Rome, Italy.
- eXtension 2019. Making and Using Compost for Organic Farming.
Benefits
- Composting is an effective and low-cost option to recycle organic matter that can improve soil nutrient health.
- Composting in scalable, based on need and available organic materials.
- Moisture and oxygen are very important. Ensure that compost materials are moist and regularly rotated to optimise decomposition conditions.
- Cover during extreme weather events (heavy rain, extreme heat, high wind etc.).
- Add earthworms to the material to increase decomposition and speed up process.
- Compost should be regularly added to soils to increase soil organic nutrients.
Drawbacks
- Developing productive compost material, with beneficial nutrient is not a quick process, and can take up to two years for productivity to reach optimal outputs.
- Faster methods require more energy and inputs as significant amounts of organic material is needed, material must be shredded/chipped, and compost piles need to be turned every three days.
- While composting is scalable, the amount of available organic material may be a limiting factor.
- Composting plant material must include removal of any diseased plant material and weed seeds should be avoided.
- Earthworms will need to be sourced to improve the productivity of composting operations.
Earthworms can be sourced from a worm farm – if worm farms are not available, you can create your own by purchasing worms from an agricultural supplier. Worm farms can also be purchased as kits.
