Making organic fertiliser from farm waste: an eco-friendly and profitable venture

A heap of dung beside the cowshed, straw and fallen leaves piling up in a corner of the yard, vegetable peel behind the kitchen. This waste collects in nearly every rural home each day, and most of it is burned or thrown into the ditch. Yet sorted and rotted the right way, it becomes good-quality organic fertiliser that raises soil fertility and helps crops yield more. Making organic fertiliser from cow dung, poultry droppings, fallen leaves, crop husks and other organic matter is at once eco-friendly, low-cost and profitable.

The state of our soil shows how much organic fertiliser is needed. According to the Soil Resource Development Institute (SRDI), most farmland in Bangladesh contains less than 1.5 per cent organic matter, while good soil should have at least 2.5 per cent. Under the pressure of two or three crops a year, what is taken out of the soil is not being put back.

Chemical fertiliser feeds plants quickly but returns no organic matter to the soil. It is organic matter that keeps soil crumbly, holds water and feeds the countless beneficial microbes and earthworms living in it. The most practical way to make up the shortfall is organic fertiliser made from farm waste.

A question often comes up: dung and poultry droppings are fertiliser already, so why go to the trouble of composting them? Because raw dung or droppings spread directly on a field give off heat and gas as they rot in the soil, which can damage young roots. They also carry weed seeds and disease organisms, and part of their nutrient content escapes into the air as odour. Properly rotted fertiliser is free of these problems, and the plant takes up its nutrients slowly and safely.

Meanwhile the straw, leaves and peel that are burned take with them organic matter that could have gone back into the soil, and add smoke and pollution besides. Gathered into a pit or heap, the same waste turns from rubbish into a resource.

The benefits of turning farm or household organic waste into fertiliser can be seen from several angles.

First, fertility rises. Organic fertiliser adds organic matter, makes up nutrient deficiencies and keeps soil fertile over the long term, supplying major nutrients such as nitrogen, phosphorus and potassium. Second, soil structure improves. It binds soil particles firmly, increases water-holding capacity, checks erosion and helps roots spread properly.

Third, crop productivity increases. Organic fertiliser supplies the nutrients crops need, strengthens roots and improves resistance to disease. Fourth, soil life flourishes. Beneficial bacteria and earthworms multiply, the soil's natural nutrient cycle recovers, and crop quality improves too.

Fifth, costs fall. It is made from waste the farm already has, far cheaper than bought chemical fertiliser. Sixth, the environment gains. Less chemical fertiliser means less pollution of soil and water, and farm waste is put to use rather than wasted. Heavy use of chemical fertiliser can in the long run upset the soil's balance of acidity and alkalinity, its pH; organic fertiliser helps maintain that balance and the soil's long-term health. Made from natural materials, it is also safe for crops.

Water hyacinth deserves a separate mention. It grows in abundance in ponds, canals and beels across the country and often becomes a burden on them. Pulled out, partly dried and layered with dung, it makes good compost material.

There is no need to look far for materials. Nearly everything is found on the farm, at home or in the local market. Broadly:

• Animal waste: dung and urine of cattle, poultry or sheep.
• Crop residue: what remains after harvesting rice, wheat, maize or other crops.
• Straw or dry grass, which supplies carbon to the heap.
• Food waste: stale food, rotten fruit, vegetable, potato and banana peel.
• Leaves and tree parts: dry leaves of neem, bakain (Persian lilac) or other trees; bark.
• Natural additives: lime to regulate pH, Epsom salt to speed decomposition, and earthworms for vermicompost.
• Soil: a little sand or a thin layer of soil, and topsoil.
• Others: wood shavings or sawdust, and paper or cardboard if needed.
• Clean water to keep the heap moist.

It helps to think of the materials in two groups. Dry, brown materials such as straw, dry leaves, bark and sawdust mainly supply carbon. Fresh, wet materials such as dung, poultry droppings and vegetable and fruit peel supply nitrogen. The microbes that do the rotting need both: carbon is their energy, nitrogen the building block of their bodies.

Much of compost's success lies in this ratio. Carbon to nitrogen should be about 30:1. With too much dry material, decomposition slows and the heap sits almost unchanged for months. With too much nitrogen, a heap of dung or peel alone, it smells and nutrients escape as gas.

Weighing materials is impractical in the field, so the eye has to judge. Alternate layers of dry and fresh material; add dry material if the heap smells and fresh material if decomposition seems slow. Following that rule keeps the ratio roughly right.

Making organic fertiliser from farm waste can be divided into a few steps.

The first is choosing the site. Pick a shaded, dry spot and dig a tank or a pit 3 to 5 feet deep. It should be on high ground where water does not collect in the rains. Direct sun dries a heap out quickly, while standing water makes it rot and stink; shade and high ground guard against both.

Whether to use a pit or a heap depends on local water conditions. In the dry season or on high ground, a pit works well because it holds moisture longer. But in low-lying areas where groundwater rises in the monsoon, a pit fills with water. There it is safer to build the heap above ground on a raised spot, ideally under a thatch or polythene roof.

The second is collecting and preparing materials: animal waste, crop residue, leaves, grass, stale food, vegetable peel, straw, dry leaves, neem leaves and bark, readied for mixing. Chopping large twigs and long straw speeds up decomposition.

The third is building the layers. Spread dry material such as straw or dry leaves at the bottom of the pit or tank, then organic waste on top, and keep building layer on layer, each about 4 to 6 inches thick. A thin sprinkling of soil or topsoil between layers brings in microbes that help start the process.

Size matters too. A very small heap cannot hold its heat, so decomposition is slow and disease organisms and weed seeds survive. A very large, tall heap starves its centre of air, and the inside rots and stinks. It is better to fill one medium-sized heap or pit at a time and then start the next beside it. While one heap matures, the other collects fresh waste, and there is always some fertiliser on hand through the year.

The fourth is keeping it moist. Water each layer enough to keep the whole mixture at 40 to 60 per cent moisture. Too dry, and decomposition slows; too wet, and dry material must be added. The home test is to squeeze a handful: if the hand gets damp but no water drips, the moisture is right.

The fifth is turning the heap, every 10 to 15 days. Turning lets air in and moves the less rotted outer material to the centre so everything decomposes evenly. While it is working, the temperature inside the heap should stay at 50 to 60 degrees Celsius. At that heat the microbes are most active, and weed seeds and many disease organisms die. Pushing an iron rod or stick into the heap and feeling it after a while gives a sense of the heat inside.

Knowing what goes on inside the heap makes the work easier to follow. In the first few days microbes multiply fast and their activity warms the heap. Then comes the hottest phase, when heat-tolerant microbes break down the soft material. As the soft food runs out the heat slowly falls, and fungi, earthworms and small creatures finish off the tougher parts. A heap that heats up again after turning is decomposing well; one that no longer warms after turning is on its way to maturity.

The sixth is completion. Within two to three months the material turns dark, the smell goes, it becomes crumbly and no single ingredient can be recognised. It is then ready for the field.

In homes where cow dung runs a biogas plant, the liquid or semi-liquid material that comes out after the cooking gas has been produced is called slurry. It too is a good organic fertiliser. Making gas breaks down part of the organic matter in the dung, but much of the nutrient content stays in the slurry. It can go straight onto the field, or be added to a compost heap with straw, leaves or water hyacinth to make the dry material rot faster. Left in the open, slurry runs into ditches and pollutes water, so using it as fertiliser is by far its best use.

An improved form of compost was developed in Bangladesh by the Bangladesh Agricultural Research Institute (BARI): tricho-compost. Spores of a beneficial fungus, Trichoderma, are mixed in while cow dung, poultry litter, water hyacinth, vegetable waste, sawdust, maize bran and molasses are composted. The fungus works against several harmful soil-borne fungi, so the compost both feeds the soil and gives seedlings some protection from disease.

According to organisations that have worked on the method, tricho-compost takes about 45 days to make in summer, when average temperatures are around 35 degrees Celsius, and up to 70 days in winter, when temperatures can fall to 10 degrees. It is now also produced and sold commercially in the country.

Another form of compost is vermicompost. Here partly rotted material, especially dung, is fed to earthworms. Red worms of the species Eisenia fetida are released into a shaded bed, tub or ring; they eat the material and the granular castings they leave are the fertiliser, ready to harvest in about 45 to 60 days.

A few points need attention in vermicomposting. Fresh dung given straight to the worms can kill them with its heat and gas, so the dung is left for some days to cool and part-rot first. Beds or tubs are kept in shade, out of direct sun and rain. The mix should be moist but never waterlogged. Ants, rats, chickens and birds prey on the worms, so covering the bed and standing tub legs in water to stop ants are good habits. When the compost is ready it is taken from the top and sieved to separate the worms, which can then start a new bed.

In Bangladesh vermicompost is also becoming a source of income for small and marginal farmers. Department of Agricultural Extension figures reported by The Daily Star put annual vermicompost production in five districts, Rangpur, Lalmonirhat, Kurigram, Gaibandha and Nilphamari, at about 55,000 tonnes against demand of about 75,000 tonnes, with some 10,000 farmers in those districts making and selling it. The gap between demand and supply shows there is still room in the market.

The same report sets out the economics. With their own dung, farmers can bring the cost of making vermicompost down to 4 taka a kilogram; with bought dung it is about 7 taka, and it sells for about 12 taka a kilogram. Worms bring extra income too, at 900 to 1,200 taka a kilogram. The report mentions that a farmer can produce up to 10 tonnes a year. In Chilmari upazila of Kurigram alone, some 600 marginal farmers are involved. A project implemented jointly by RDRS Bangladesh and Cordaid with European Union funding trains farmers and distributes worms to new producers.

A few do's and don'ts matter while making organic fertiliser:

• Neem leaves, lime or Epsom salt can be added to speed decomposition.
• Do not add any chemical fertiliser or pesticide to the mix; it destroys the fertiliser's natural qualities and useful microbes.
• Cover the pit or heap with polythene or tarpaulin in the rain, or nutrients wash out and the heap gets waterlogged.
• Mix carbon (dry material) and nitrogen (fresh waste) in the right proportion.
• Make only as much as you need; fertiliser stored too long can lose quality.

Some signs during the process show what is wrong with a heap, and the fixes are close at hand:

• A rotten-egg smell: the heap is too wet or too rich in nitrogen. Mix in dry straw or leaves and turn it.
• A sharp smell of ammonia: too much fresh waste. Add more carbon-rich dry material.
• A cold, dry heap where nothing rots: short of water and fresh material. Sprinkle water, mix in dung and turn it.
• Flies or insects: food waste is lying exposed. Bury it inside the heap and cover the top with soil or dry leaves.

Before food waste goes in, pick out polythene, plastic, glass and metal. These do not rot; they spoil the fertiliser and later damage the soil in the field.

Applying it also has rules. Mixing 3 to 5 tonnes of organic fertiliser per hectare into the soil at land preparation gives good results. How much a given crop needs, and how far chemical fertiliser can be reduced, is best decided with a soil test and the advice of the upazila agriculture office.

The finished fertiliser is not only for field crops. It serves home vegetable gardens, fruit-tree pits and potted plants as well: mixed into soil when making vegetable beds, into the pit before planting a fruit sapling, or as part of the potting mix. Everywhere, organic fertiliser keeps the soil crumbly and alive, and any surplus beyond a household's own needs can be sold to neighbours.

Timing needs thought as well. A compost heap takes two to three months to mature, so work has to start at least three months before the season in which the fertiliser is needed. To have it ready when preparing land for winter vegetables or potatoes, for example, it is best to start building heaps towards the end of the monsoon. Without planning ahead, there is no fertiliser at hand when it is needed, and the farmer is pushed back towards bought fertiliser.

Making organic fertiliser from farm waste can put farming on a sustainable footing. It raises output while cutting costs, protects soil health and reduces pollution. Relying less on chemical fertiliser and more on organic makes farming more eco-friendly and more sustainable.

The dung heap beside the cowshed at the start of this report, given the right place, the right layers, measured water and a few months of patience, becomes the cheapest and most lasting food a field can have.

Photo: Compost worms (Eisenia fetida), Toby Hudson / Wikimedia Commons (CC BY-SA 3.0)