Sustainable Agriculture Extension Manual

Composting

Composting means piling up crop and other farm wastes in layers to make them decompose quickly.

Composting is done to produce an organic fertilizer that is balanced in plant nutrients. This organic fertilizer, known as humus, improves soil fertility, moisture retention and soil aeration.

Location

Compost can be used in all soils with low fertility. It is especially good in areas that have low rainfall, where artificial fertilizers cannot be used effectively because of lack of moisture. It is also useful in sandy soils which have poor water-holding capacity. Compost improves the structure and drainage of all soils.

Advantages

Large amounts of vegetation, such as crop remains, garden weeds, kitchen and household wastes, hedge cuttings, garbage, etc, are put to use.
When properly made, compost becomes immediately available as plant food without the need to be first broken down by soil microorganisms.
Compost does not cause excessive weed growth, as is the case with ordinary farm manure.
Good crops can be obtained without the need for extra chemical inputs.
All farmers, regardless of their financial abilities, can make and use compost.

Disadvantages

Compost requires a lot of labour to prepare and spread it over the farm.
The nutrient composition of the compost varies a great deal. It depends on the materials used and the preparation methods (see Using organic matter).
Not enough vegetation to make compost may be available in drier areas.

Requirements

Various types of vegetative materials.
Topsoil.
Animal manure or biogas slurry.
Wood ash.
Water.
A long, sharp, pointed stick.
Wheelbarrow, watering can, hoe, machete.

Pile method

This method is suitable for areas with higher rainfall. For low-rainfall areas, use the pit method (described later in this section).

Select a location close to where you want to use the compost. The place should be sheltered from the wind, rain, sun and runoff. A compost pile must not get either very dry or very wet.
Measure a rectangle 120 cm (4 feet) wide and 150 cm (5 feet) or more long (the length depends on how much composting material you have). Do not make the rectangle wider than 120 cm, as you must be able to work on the compost without stepping on it. In rainy places, it is best to make compost in a pile above the ground. In drier areas, use the pit method described later in this section.
Dig a shallow pit about 30 cm (1 foot) deep. Put the soil on one side (you will need it later).
Begin building a compost pile by putting a bottom layer of rough materials such as maize stalks and hedge cuttings in the pit. This layer should be about 30 cm thick. Chop up any materials which are too long to improve the air circulation in the pile. Sprinkle some water on this layer.
Add a second layer of dry vegetation, hedge cuttings or grass. This layer should be about 15 cm (6 inches) thick. Sprinkle water on this layer, too. You should sprinkle water on each layer as you add it. The pile should be moist throughout.
Put on a third layer of animal manure or biogas slurry. The manure contains micro-organisms which are vital for decomposition.
Sprinkle some ash or dust on this layer. The ashes contain valuable mineral including potassium, phosphorus, calcium and magnesium. The ashes also neutralize the acids produced during decomposition, especially by the animal manure.
The next layer should be of green materials about 15-20 cm (6-8 inches) thick. Use green leaves from high-protein leguminous trees like calliandra, leucaena and sesbania. You can also use hedge cuttings of plants like tithonia.
Sprinkle on a little topsoil or old compost. The topsoil contains bacteria which are

useful in the decomposition process.

10. Add more layers in turn, starting with dry vegetative materials, then animal manure or biogas slurry, followed by wood ash, green vegetation and topsoil. Remember to sprinkle water on every layer. Build the pile up to 1.5 m (5 feet) high. A well-made pile has almost vertical sides and a flat top.

11. To complete the pile, cover it all over with a layer of topsoil about 10 cm (4 inches) thick. This layer prevents plant nutrients from escaping from the compost pile. Lastly, cover the whole with dry vegetation such as banana leaves to reduce moisture loss through evaporation.

12. Take a long, sharp, pointed stick and drive it in at an angle so that it passes through the pile from top to bottom. This stick will act as your "thermometer". After three days, decomposition will have started in the pile, and the stick will be warm when you pull it out.

13. Pull the "thermometer" out from time to time to check the progress of the pile. You can also tell from the thermometer how dry or wet the pile is: it should be moist but not wet.

14. Sprinkle water on the pile occasionally (about every 3 days, depending on the weather). If it has been raining, you may not need to water the pile.

Turn the pile after 2 weeks

15. After 2-3 weeks, turn the pile over. Do not add any fresh materials except water. You must turn the pile if the "thermometer" is cold when you pull it out, or if it has a white substance on it, as this shows that decomposition has stopped. Turning the pile is important because it mixes the different layers, making the decomposition faster and more complete.

16. The compost should be ready after 4 weeks. Check the temperature of the pile to make sure. If the stick feels warm when you pull it out, the pile is still decomposing and the compost is not ready. Finished compost should have a fresh, earthy smell and contain no grass, leaves, or animal manure.

17. You can store compost by covering it with a layer of banana leaves or polythene.

Do's

Choose a sheltered site for the compost pile.

Chop up long stems and big leaves.

Sprinkle some water on every layer, and ensure that the compost is moist all the time.

Turn the pile every 3 weeks.

Protect the finished compost from sun, wind and rain.

Don'ts

Don't use materials that might contaminate the soil.

Don't step on the pile.

Don't use waxy leaves (such as eucalyptus leaves).

Don't over-water the compost pile.

Don't compact the layers.

Don't use materials that do not decompose.

Pit method

The pit method of making compost conserves moisture, so it is useful in areas with low rainfall and a long dry season. Do not use it in wet areas, as the compost may become waterlogged.

1. Dig a pit 1.2 m (4 feet) wide and 0.6 m (2 feet) deep, and as long as you need for the amount of materials you have.

2. Build a pile in the pit, using the same method as in the pile method (see above).

3. Add water if necessary.

4. Push long poles into the pile to allow air to get into the layers beneath.

5. Turn the pile every 2 weeks.

You can produce a regular supply of compost by digging three pits side by side. Every 2 weeks, turn the compost from one pit into the next one, and start a new compost pile with fresh vegetation in the empty pit.

Using compost

Well-decomposed compost should be applied at the rate of 20 t/ha (8 t/acre): about two large hoefuls per square meter, or enough to barely cover the ground with a layer 1 cm (0.4 inch) thick. For potatoes, use 1 tin (about 20 kg) for about 2 m (6 feet) of furrow. In double-dug beds (see the section on Deep soil preparation), apply 3 wheelbarrows of compost on 10 m² (100 square feet) of beds.

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