There are many benefits to making compost which is essential in building soil health. Compost is a low cost input because the components like ash, fresh and dry grass, animal dung, soil and water are all on-farm.
- Compost contains important nutrients for plant growth, like nitrogen, phosphorus and potassium and micronutrients.
- Adding organic matter improves soil structure and gives soil a greater capacity to hold water and air.
- Compost improves crop quality and reduces fertiliser and pesticide costs.
Compost forms when plant and animal material is broken down into simpler components by aerobic bacteria, micro-organisms and insects. The decomposition process makes the nutrients more available to plants. Ideally the compost should be dark and have a crumbly texture and a rich, earthy smell when it is ready.
Compost releases its nutrients slowly, and over a longer time than synthetically produced fertilisers and can be successfully used with the fertiliser.
The living organisms responsible for the composting process need oxygen to survive, so that fast decomposition takes place. Add some dry, chunky materials to your compost like old leaves and stalks to create space for air to circulate through the compost. Green grass clippings can easily form a mat that cuts off air supply, so mix it with materials like wood shavings or straw.
Maintain good water to material ratio, with enough water to keep the materials moist and wet. Too much water causes the compost to rot, and the mixture smells bad. Too little slows down the composting process.
If you live in a dry area, add some water from time to time to maintain the moist conditions. Cover the heap to prevent too much water from entering the heap when living in a wet climate.
Water from any source can be used, including collected rainwater, animal and human urine or water from ponds, rivers and streams. Don’t use precious drinking water if you have these options.
During the process of decomposition microbes produce heat. If your compost heap is working, it should heat up after a few hours.
The heat destroys weed seeds, fungal diseases, pests and parasites.
An insulation layer can be used to cover the heap and contain the heat. Black plastic traps heat and moisture and also captures the heat from the sun.
Ash is a good mix because it contains phosphorous, potassium and micro-nutrients like zinc, iron and magnesium. Distribute the ash evenly because it contains a high concentration of minerals that can slow down or stop micro-organism activity.
Top soil and old compost
Old compost and healthy forest soil contains the healthy microbes you need for making compost and is a good kick-starter for your compost heap.
Mix some dry top soil, old compost and ash. Crush it and if possible pass it through a sieve until you have a fine powder.
Mix this powder with fresh composting materials, like the dry and green plant materials and put this in a layer between the other layers. Do not put the composting aid in as a separate layer.
Micro-organisms (fungi and bacteria) and small animals (including earthworms, nematodes, beetles and other insects) can turn waste material into compost. They occur in naturally healthy soil from forests, old animal dung and old compost. You can add some of them to your compost to help with the decomposition process.
Use any dung or droppings from your farm animals, collected in their pens or from the field, including the dung of pigs, sheep, chickens, cattle and horses.
Collect urine from animals early in the morning when they start to move. Animal dung contains several important nutrients like nitrogen, phosphorous and potassium, micro nutrients and water.
If you don’t have animal material available it is still possible to produce good quality compost by using only plant material or kitchen waste.
The nitrogen to carbon ratio must be maintained in your heap. The nitrogen comes from green material and carbon mostly from brown material.
- Any fresh green leafy material such as grass, weeds, plant residues.
- Waste from cleaning grain, cooking and making food or drinks, like coffee, tea or homemade beer.
- kitchen waste like egg shells, vegetable peels and cuttings.
- If you use thick, woody plants, chop them into smaller pieces for faster decomposition.
- Remember – plants with strong essential oils like eucalyptus might kill microorganisms.
- Crop residue – stems, leaves, bran and husks from the harvest of cereal, pulses, oil crops and horticultural crops.
- Hay and straw left over from feeding and bedding animals. Animal bedding is already mixed with animal urine and manure, so is a good material for your compost.
- Sawdust and wood chips.
Selecting a site
- The area should be easily accessible for setting up the pile and for maintenance.
- Choose an area with a good balance between sun and shade, so the heap is not too dry or wet. This would be under a tree or on the west or north side of a building or wall.
- Clear the site of stones, weeds and grasses, but don’t cut down any trees, rather use them as shade.
- Mark the area for your site, the size can range from between 1.25 m x 1.25 m to 3 m x 2.5 m.
- Wet the ground where you plan to make the heap. This prevents the soil underneath from absorbing moisture from the heap, and also allows earthworms and insects to penetrate the heap from beneath.
The layers of the compost heap
Place a layer of twigs or coarse material, about 5 to 10 cm thick, on the base where you plan to build your heap. This allows for air to circulate from the bottom and for excess water to seep out.
Building the layers
Start building your heap by alternately placing layers of ‘green’ and ‘brown’ on top of each other. Each layer should be 10 cm to 15 cm thick. Mix the different materials within each layer properly to allow for aeration and to prevent matting.
Wet each finished layer to make it moist.
Try to maintain a ratio of 50:50 between green and brown materials.
Monitoring the compost heap
The microbes start their work immediately and the heap should heat up within a few hours.
Use a “testing” stick to assess the temperature of the heap. Insert a stick – longer than the height the heap, into the centre of the heap and just pull out to feel the temperature of the heap.
If your compost heap is not heating up, there might be something wrong with the composition.
Keep an eye on the moisture content – it must feel like a wrung out cloth, and there must be enough moisture to almost drip when you squeeze a handful.
The pile can be turned regularly to shorten the composting time. Turning allows for more aeration and brings all the materials in contact with the hot centre. The heap should be turned when there is a decrease in the temperature of the centre. Wet the heap after turning. Correct turning is when the inside is out and the outside of the heap in.
When is the compost heap ready?
- Depending on the season, and also your climate it can take from 3 months to 12 months for a compost heap to mature.
- The heap is ready when the compost heap doesn’t heat up again after turning. You should not be able to make out the original contents of the heap.
- The finished product looks like dark soil and should have an earthy smell, like the forest soil. When the compost heap starts smelling bad, something is wrong.
- The finished heap should also have halved almost in size.
Compost can be added as mulch when applying conservation agriculture techniques. Small insects and earth worms will gradually work it into the soil for your plants to use.
- This article was compiled using information from the South African Agricultural Research Council and the United Nations Food and Agricultural Organisation.