Natural fertilizer provides the food needed for a plant to grow after a seed has germinated in the soil. This food consists of plant nutrients. The most important of these nutrients are nitrogen (N), phosphorus (P) and potassium (K). There are also many other chemicals needed by plants in small quantities, e.g. copper (Cu), manganese (Mn), magnesium (Mg), iron (Fe), sulphur (S) and others. These are called micronutrients or trace elements. Natural fertilizer also provides organic matter called humus for the soil.
Humus is a black or brown spongy or jelly-like substance. It helps the soil have a good structure to hold water and air. One of the best natural fertilizers is mature compost because it feeds the soil with humus and plant nutrients. The growing plants take their nutrients from the top layer of the soil where their roots grow. Plant nutrients are lost from the soil when they are washed down (leached) below the top soil, or when the top soil is eroded. Plant nutrients are also lost with the crops when these are harvested. When the surface of the land is broken up for farming, the soil is often eroded: it is blown away by the wind or washed away by rain and floods. The soil also loses much of its carbon content as carbon dioxide (CO2) into the atmosphere, thus contributing to climate change.
The soil that is left becomes poor in plant nutrients so the crops do not grow well and give a good yield. But if the plant nutrients and carbon are returned to the soil, it can continue to grow good crops as well as contribute to slowing down the negative impacts of climate change. Farmers can replace the lost plant nutrients by using fertilizers. Natural fertilizer comes from animal wastes and plants; for example, cow dung, sheep, goat or chicken droppings, urine, decomposed weeds and other plant or animal remains, e.g. waste from preparing food. The fertilizer can also be made of chemicals in a factory. Farmers in Kenya have to buy this type of fertilizer from agrovets or through NCPB.
Therefore fertilizers are of two types:
- Natural fertilizer, including compost
- Chemical fertilizer (Human Made)
Throughout the world there are many options for replacing the plant nutrients lost from soil, but, in our case in Kenya and in many other parts of Sub-Saharan Africa where most of the agriculture is done by smallholder farmers, the best option is compost produced by human labour using the natural materials available to farmers and others, such as students and youth, from their surroundings. Good quality compost can be made from organic household wastes in urban areas and be used to grow healthy vegetables in gardens at home or by school environment club or youth group members.
Why is compost important?
Compost is important because it:
- Contains the main plant nutrients – nitrogen (N), phosphorus (P) and potassium (K), often written as NPK.
- Improves the organic matter in the soil by providing humus.
- Helps the soil hold both water and air for plants.
- Makes trace elements or micronutrients available to plants.
What can compost be used for?
Because compost is made up of humus, it can be used for improving soil as follows:
It provides plant nutrients that are released throughout the growing season.
- The plant nutrients are released when organic matter decomposes and is changed into humus.
- The plant nutrients dissolve in the water in the soil and are taken in by the roots of the crops.
It improves soil structure so that plant roots can easily reach down into the soil.
- In sandy soil the humus makes the sand particles stick together. This reduces the size of the spaces (pores) so that water stays longer in the soil.
- In clay soils, the humus surrounds the clay particles making more spaces (pores) in the soil so the root systems of plants can reach the water and nutrients that they need, and air can also move through the soil.
- Therefore, because heavy clay soils become lighter and sandy soils become heavier, soil that has had compost added to it is easier to work, i.e. to plough and dig.
It improves the moisture-holding capacity of soil.
- The humus is a dark brown or black soft spongy or jelly-like substance that holds water and plant nutrients. One kilogram of humus can hold up to six litres of water. In dry times, soil with good humus in it can hold water longer than soil with little humus. In Kenya, crops grown on soil with compost can go on growing for two weeks longer after the rains have stopped than crops grown on soil given chemical fertilizer.
- When it rains, water easily gets into the soil instead of running off over the surface.
- Water gets into the subsoil and down to the water table, runoff and thus flooding is reduced, and springs do not dry up in the dry season.
It helps to control weeds, pests and diseases.
- When weeds are used to make compost, the high temperature of the compost‑making process kills many, but not all, of the weed seeds. Even the noxious weed, Parthenium, has most of its seeds killed when it is made into compost following the instructions given in this document.
- Fertile soil produces strong plants able to resist pests and diseases.
- When crop residues are used to make compost, many pests and diseases cannot survive to infect the next season’s crops.
It helps the soil resist erosion by wind and water. This is because:
- Water can enter the soil better and this can stop showers building up into a flood. This also reduces splash and sheet erosion.
- Soil held together with humus cannot be blown away so easily by wind.
Compost helps farmers improve the productivity of their land and their income.
It is made without having to pay cash or borrow money, i.e. farmers in Kenya do not have to take credit and get into debt like they do for taking chemical fertilizer. But, to make and use compost properly farmers, either individually or working in groups, have to work hard.
What is needed to make compost?
Plant materials, both dry and green
- Weeds, grasses and any other plant materials cut from inside and around fields, in clearing paths, in weeding, etc.
- Wastes from cleaning grain, cooking and cleaning the house and compound, making food and different drinks, particularly coffee, tea, home-made beer, etc.
- Crop residues: stems, leaves, straw and chaff of all field crops – both big and small – cereals, pulses, oil crops, horticultural crops and spices, from threshing grounds and from fields after harvesting.
- Garden wastes – old leaves, dead flowers, hedge trimmings, grass cuttings, etc.
- Dry grass, hay and straw left over from feeding and bedding animals. Animal bedding is very useful because it has been mixed with the urine and droppings of the animals.
- Dropped leaves and stems from almost any tree and bush except plants which have tough leaves, or leaves and stems with a strong smell or liquid when crushed, like Eucalyptus
- Stems of cactus, such as prickly pear, can be used if they are crushed or chopped up. They are also a good source of moisture for making compost in dry areas. When the compost is made correctly, the spines are destroyed.
Enough water is needed to wet all the materials and keep them moist, but the materials should not be made too wet so that they lack air and thus rot and smell bad. Both too little and too much water prevent good compost being made. Water does NOT need to be clean like drinking water.
It can come from:
- Collected rainwater.
- Collected wastewater.
- Animal urine or Human urine.
- Ponds, dams, streams and rivers.
- Dung and droppings from all types of domestic animals, including from horses, mules, donkeys and chicken, from night pens and shelters, or collected from fields.
- Chicken droppings are important to include because they are rich in nitrogen.
- Urine from cattle and people- Catch urine in a container from animals when they wake up and start moving around in the morning.
- Night soil (human faeces): almost all human parasites and other disease organisms in human faeces are killed by the high temperatures when good compost is made.
Compost Making Aids
Micro-organisms (fungi and bacteria) and smaller animals (many types of worms, including earthworms, nematodes, beetles and other insects) turn waste materials into mature compost. These are found naturally in good fertile soils like those from forests, old animal dung and old compost. Adding any of these to new compost helps in the decomposition process. Adding compost making aids is like adding yeast to the dough to make bread. The farmers in Ethiopia call these materials the ‘spices’ to make good compost.
Including dry materials in the compost, e.g. old leaves and stalks, provides space for air to circulate inside the compost. Air is needed because the soil organisms need oxygen.
Decomposition of organic wastes produces heat. Compost needs to be kept hot and moist so the plant and animal materials can be broken down quickly and thoroughly. Heat destroys most of the weed seeds, fungal diseases, pests and parasites.