Compost is the product resulting from the controlled biological decomposition of organic material. Compost is made through a natural process where organic matter is broken down to form humus. The composting process provides an excellent source of nutrients for replenishing the soil. It offers a cheap way of ensuring soil fertility management without the need for use of expensive external inputs such as chemical fertilizers.
The requirements for composting are the presence of soil microorganisms and organic material such as animal manure (farm yard manure) crop remains or residue, municipal garbage, kitchen waste, hedge trimmings, and weeds, which do not have seeds. Moisture must also be present to speed up the decomposition, and temperature control to optimize microorganism activity and aeration of the soil to provide adequate oxygen for the decomposition process.
The composting process has three stages:
Composting should be a continuous process on the farm depending on the availability of composting material. Farmers are advised to prepare compost when there is plenty of such material on the farm. Such compost can be stored for use when it is needed. It should be kept covered with a polyethylene sheet, banana leaves or any other vegetative material until it is needed for application in the shamba.
Green manures are plants grown as food for people and feed for animals while improving the soil. The plants may fix nitrogen, protect soil from drying, improve soil structure through the roots and suppress weeds since they grow fast. Green manures can also control pests since they create a habitat for predators. The plants can be ploughed back into the soil or cut and left to be used as mulch later.
Examples of green manure plants include purple vetch, calliandra, leucaena, mucuna, lucerne, desmodium. Legumes such as soybeans, green grams, groundnuts and pigeon peas, cowpeas etc. All plants require nitrogen to grow; plants get the nitrogen from the soil and store it in their leaves, stems and roots.
The main advantage of legumes is that they can capture their own nitrogen from the air and fix it into the soil. When intercropping, it is very important that farmers use green manure plants as they increase the amount of nitrogen in the soil. Research conducted by KALRO in Kenya shows that legumes such as mucuna, lablab, crotolaria and canavalia planted alone can add 35 – 150kg of nitrogen into the soil per hectare.
Mandala kitchen garden for the dry season
Getting vegetables during the dry season is a big problem for farmers. This is because most farmers rely on rain to grow their food crops. Come the dry season and many rural households have no reliable source of vegetables as lack of water ensures nothing grows at this time. For those farmers without a river frontage (a farm near a river), there are various methods they can use to grow vegetables. One of these is putting up a Mandala garden, named after a farmer in Elitrea who pioneered the first garden of this nature.
A Mandala garden is a small circular kitchen garden made close to the house where the farmer can use water from the kitchen to water the garden and grow such vegetables as sukumawiki, spinach, tomatoes, chillies or any other crops that they need. The seed bed is prepared through digging to make sure the soil is good enough to retain water and the right texture. With a stick and rope, the farmer can make the outline of a circular garden in the seedbed. A watering hole is then made at the centre of the circle. A number of furrows and ridges 2 ft apart are then made following the circular outline. A small water channel is then made stretching from the kitchen to the watering hole at the centre of the circle. The garden is first watered and the desired vegetables planted on the ridges, all the waste water from the kitchen flows into the hole where it is used to irrigate the garden.
To protect the garden from the animals, the farmer can make a hedge around it or even use a net to protect it against birds. Through the use of Mandala gardens households have constant supply of green vegetables through the dry season.
Soil fertility management practices for better soils
The principles of organic agriculture are based on a simple premise: “Feed the soil, to feed the plants”. As such, one of the most important tasks in organic farming and sustainable agricultural production is to increase the level of soil fertility. To be successful, farmers need to adopt practices that focus on improving soil productivity on their farms. These include;
Soil and water are the most important productive factor for crops. It is a living system. Therefore, soil cultivation should aim at minimum disturbance of the soil life. The most important reasons for cultivating the soil are to:
Let the soil breath
Like humans, soil organisms are required for healthy soils. Plant roots also need oxygen to breathe. Mixing mulch, compost or manure into the soil is important, they improve aeration. Micro-organisms, insects, worms and other animals improve air circulation in the soil.
Mulching conserves water and enriches soil
Mulching is a method to protect and to feed the soil. It is the process of covering topsoil with plant material such as leaves, grass, twigs, crop residues, straw etc. Mulch protects the soil from wind and water erosion, it improves the infiltration of rain water, no crust is formed and keeps the soil moist by reducing evaporation. While decomposing, organic mulch material continuously releases its nutrients thus fertilizing the soil. Apart from these, mulch is transformed to humus. If the process of decomposing is to be accelerated, organic manures such as animal dung may be spread on top of the mulch, thus increasing the nitrogen content.
Mulching has a lot of advantages, but it can be problematic if not done well. For example, green vegetative matter should not be used as it may encourage pests and diseases. Harmful organisms such as stem-borers may survive in crop residues. Plant material infected with viral or fungal diseases should not be used if there is a risk of a disease being transmitted to the next crop. Crop rotation is the best way to avoid these risks.
Take care of water
Water is a blessing, but too much water is detrimental to plant growth. Soil erosion is a serious threat to soil fertility. It carries away topsoil, the most fertile parts of the soil.
Apart from mulching, cover crops are the most effective method of stopping soil erosion. The water drops reach the soil with less speed and therefore have a lesser smashing affect on soil crumbles, reducing the possibility of a run-off.
At the same time, cover crops act like a sun shade. Every plant which covers the soil and improves soil fertility can be a cover crop. For instance, leguminous plants enrich the soil with nitrogen: A crop like cowpea is drought tolerant, can fix nitrogen, yields eatable grains and can be used as an animal feed which is rich in protein. In addition, it is resistant to pest attacks.
Feed the soil to feed the plant
This is the most important task for every farmer: to feed the soil with compost, manure and green manure (leguminous plants). Overused and unfed soils are dead soils.
Crop rotation is planting of different crops in the same field in consecutive seasons. If, for example, the land has been planted with maize and beans one year, the farmers can rotate these by planting another crop the following year or in the next season. The most suitable crops for rotations are legumes or fodder crops such as Lucerne, Desmodium, Mustard e.t.c, which help improve soil fertility.
Agroforestry is an ecological method of land resource management that involves the growing of both crops and trees on the same land. It is the integration of trees into cropping systems to create diversity in production, more and diverse income for farmers, healthy foods and sustainable land management. It is implemented in any size of land and does well among smallholder farmers.
Agroforesty makes use of a wide range of trees used for diverse functions that include providing firewood, fruit, livestock fodder, plant extracts for medicinal purposes and improve soil fertility. Majority of the trees used in agroforestry, grow back when cut, hence, able to continue providing herbage and wood. Some of these trees include: grevillea, luceana, calliandra, acacia and sesbania sesban.
Today, trees in farms are seen as a crucial bridge between forestry and agriculture, striking a balance between conservation and production. While Africa’s forests diminish, more trees are being planted in farms, and small scale farmers are doing this for their own benefit and that of the environment. In many countries, agroforestry is seen as a strategy to compliment forest cover and increase the area under trees.
It is crucial to incorporate trees which are fast maturing, have the ability to fix nitrogen in the soil and which do not compete with crops, but bring in multiple benefits to livestock, crops, soil, and the environment at large; they are Nitrogen Fixing Trees. The acacia tree, for instance has long been combined with traditional farming in Africa. Scientifically, known as Faidherbia albida, or “Mgunga” in Swahili, the acacia possesses the unique ability to produce the much needed nitrogen for soil and plants. It goes dormant and sheds its nitrogen-rich leaves during the early rainy season, when crops are being planted, and resumes leaf growth in the dry season.
The trees are able to utilize the atmospheric nitrogen through an association with a Rhizobium, a bacterium which is hosted in the root system of nitrogen fixing trees. These plants biologically accumulate nitrogen by pulling essential nutrients out of the air for their own use, and if managed well, can make it available to other crops as well. This reduces the need for commercial nitrogen fertilizers.
During the dry season, some trees are able to shed their leaves, while others remain green, which can be used to feed livestock. Producing staple food crops like maize, sorghum and millet under these agroforestry conditions dramatically increases their drought resilience in dry years because of the positive soil moisture and better microclimate.
The fallen leaves, weeds and crop residues do not go to waste. They are heaped to naturally decompose and later used to fertilize the farm. After they are heaped, they usually attract many beneficial microorganisms, which feed on them. The microorganisms contribute to enriching and improving soil for plants, animals and even humans. Earthworms, for example, create tunnels in the soil by burrowing, which aerates the soil to allow air, water and nutrients to reach deep within the soil. Earthworms eat the soil which has organic matter. After the organic matter is digested, the earthworms release waste from their bodies, called castings, which contain many nutrients for the crops. As an important addition to their other roles, trees not only act as natural fertilizers, but as niche for these hardworking earthworms and microbial life.
Through constant pruning and cutting firewood, one is able to increase the organic matter (leaves) in the soil, which act as mulch, keeping it moist and well aerated, and increases the activity and population of microbial life in the soil. The leaves also act as humus, a very important feature in building soil fertility.
Trees are also able to suppress weeds, reducing the time and energy needed for weeding, and promoting “easy to work” soil. Other trees, like luecena, attract bees during flowering. While collecting nectar, they help in pollination and repelling harmful insects.
Agroforestry represents a wide diversity in application and in practice. Trees can be widely scattered over a large agricultural plot or pasture or crop strips alternate with rows of closely spaced tree or hedge species. Normally, the trees are pruned before planting the crop. The trees can also act as living fences and windbreaks.
With growing concerns about how smallholder farmers can continue to feed themselves in their small farms without destroying local ecosystems agroforestry is the best thing to happen to sustainable farming.