IntroductionComposting organic wastes isan environmentally sound means of recycling raw organicmaterials into valuable soil amendments with many uses.
What is composting?Composting is the process of producingcompost through aerobic decomposition of biodegradable organic matter.Compost produced at the end of the process can be used in farming and gardening to improve soil quality.
Principles of CompostingComposting is the controlled decomposition oforganicmatte
Type of composting Active (hot) composting • ~55oC – Higher temperature kill most pathogens – Regularly stirring ensure aeration – Faster (take weeks) – Passive (cold) composting • ~30oC – Much slower (may take months) –May develop anaerobic condition, releasing odor and – greenhouse gas (e.g. methane)
Carbon : Nitrogen ratioHigh-carbon sources provide the cellulose neededby the composting bacteria for conversion tosugars and heat. (e.g. starch and cellulose)High-nitrogen sources provide the mostconcentrated protein, which allow the compostbacteria to survive and multiply. (e.g. animalmanures, fruit and vegetable trimmings, leaves)The most rapid composting occurs with theideal carbon:nitrogen ratio of 25~30: 1 by drychemical weight.
Why use compost?• Composting is a method of stabilizing organic wastes by the action of microorganism• Increasing soil organic matter 30t/ha compost provides ~ 6 t/ha of organic matter = long- term benefits for soil structure, fertility and water holding• Slow release nutrients 30 t/ha compost is worth ~ £90/ha• Increasing soil microbial population• Stabilizing soil pH (fertilizers acidify soil) Better crop establishment & yields
The composting process Collection of suitably balanced feedstock materials Shredding Composting Maturation Screening Application of finished product
Material flow for the conventional composting process.Distributed by: Information Packaging Centre Alberta Agriculture, Food and Rural Development 7000 - 113 Street,Edmonton, Alberta Canada T6H 5T6
How does composting work?
Types of composting-Farmyard manure (FYM)-Poultry Manure-Cattle slurry-Town refuse-Sewage sludge
Characteristics of compost General properties of green waste compostpH 8.6Electrical conductivity (dS cm-1) 0.773Dry matter (%) 59Density (kg L-1) 0.5Organic matter (%) 19
An example of the effects on crop yieldsYield (percent of control) Potatoes Onions Cabbages Carrots
Effects on soil structure• Organic matter additions improve soil structure on both heavy and light land.• This has beneficial effects on water holding capacity, drainage, erosion and root penetration.• Cultivations are made easier.
Effects on soil biology• Biological activity is stimulated by the addition of nutrients and by the improvement to soil structure• Some evidence suggests that there can be inhibition of plant diseases
ConclusionsComposting can be an effective way of managing organic wastes.On-farm composting is a useful technique for dealing with farm generated wastes – bringing in material from elsewhere can be a good business in itself.Application of compost adds to the organic matter in the soilCompost is a good source of available P and K.The nitrogen it contains is in a stable state and relatively unavailable in the short term.