How to Make Compost from Farm Waste: Pit and Heap Methods for Farmers

After the harvest, a Bangladeshi farm is left with piles of straw and stalks, weeds pulled from the field, cow dung and urine in the cattle shed, and peelings from the kitchen. The Bangladesh Agricultural Research Council (BARC) noted in its Fertilizer Recommendation Guide-2024, published in September 2024, that in most cases crop residues are burnt or removed to clean the land, and that a big portion of the country's cow dung is used as fuel. Both are lost to the soil.

This guide, written in December 2024, explains how that waste becomes compost: why Bangladesh's soils need organic matter, what compost contains, which materials to use, the conditions decomposition needs, BARC's heap method, the classic pit methods described by Tamil Nadu Agricultural University (TNAU) and the Food and Agriculture Organization of the United Nations (FAO), the animal waste problem, and how to judge and use the finished compost. Every measurement comes from one of those authorities.

Soil organic matter comes from plant and animal remains. BARC's guide calls it the life force of a soil: it improves soil structure, water-holding capacity and aeration, it stores plant nutrients, chiefly nitrogen, phosphorus and sulphur, and it feeds beneficial organisms such as nitrogen-fixing bacteria and earthworms.

According to the guide, a good soil should have at least 2.5 per cent organic matter, but most soils in Bangladesh have less than 1.5 per cent, and some have even less than 1 per cent. Citing a 2020 study by Hasan and colleagues, it classes the organic matter status of the country's soils as very low on 0.408 million hectares (4.7 per cent of arable land), low on 2.58 million hectares (30.1 per cent) and medium on 5.08 million hectares (59.2 per cent).

BARC attributes the low carbon reserves of Bangladeshi soils to rising cropping intensity, fast decomposition in the subtropical humid climate, low use of organic manure and little or no green manuring.

TNAU's agricultural technology portal defines compost simply as a mass of rotted organic matter made from waste. BARC's guide gives a fuller definition: the organic fertiliser produced by decomposing different waste materials of plant and animal origin.

Compost is not a concentrated fertiliser. TNAU puts the average content of farm compost at 0.5 per cent nitrogen (N), 0.15 per cent phosphate (P2O5) and 0.5 per cent potash (K2O). Town compost, made from town refuse such as night soil, street sweepings and dustbin waste, contains 1.4 per cent N, 1.0 per cent P2O5 and 1.4 per cent K2O.

BARC's guide gives figures measured for Bangladesh, expressed as the elements rather than oxides. Rural compost, at about 40 per cent moisture, contains about 0.75 per cent nitrogen, 0.6 per cent phosphorus and 1.0 per cent potassium. Urban compost has about 1.5 per cent nitrogen, 0.6 per cent phosphorus and 1.5 per cent potassium, and water hyacinth compost, at about 70 per cent moisture, about 1.5 per cent nitrogen, 0.8 per cent phosphorus and 3.0 per cent potassium.

Because only part of these nutrients becomes available to a crop, the guide also estimates the supply from one tonne of rural compost: about 2.5 kg of nitrogen, 1.0 kg of phosphorus and 3.0 kg of potassium.

BARC lists a wide range of organic wastes available in the country. Domestic wastes include non-edible vegetable, food and fruit parts and after-meal leftovers. Farmyard wastes include cattle dung and urine, feed and fodder refuse, harvested crop residues and poultry excreta. Agro-industrial wastes include sugarcane trash, oil cakes, bagasse, molasses, bone meal, blood meal, fish meal, rice husk, bran and sawdust. Farm wastes include crop residues, weeds, dead animals and water hyacinth, and city wastes include solid waste and sewage sludge.

For compost in particular, the guide names dead leaves, straw, weeds, water hyacinth, household waste, municipal garbage, sawdust, leather factory waste, sugar mill bagasse and rice husk. It adds a warning: municipal and leather wastes should be treated to free them from heavy metals and other toxic substances before use.

BARC gives rice straw at about 0.4 per cent nitrogen, 0.1 per cent phosphorus and 1.5 per cent potassium. Straw, sugarcane trash and rice husk decompose very slowly, so the guide says small quantities of urea and triple superphosphate can be added to hasten their rotting. It gives no fixed rate for this, so a farmer should ask the local agriculture officer how much to use.

FAO's 2003 manual On-farm composting methods, describing the Indore method, advises that hard woody material such as cotton and pigeon-pea stalks should not exceed 10 per cent of the material.

FAO's manual sets out in figures the conditions the composting micro-organisms need.

• Carbon to nitrogen ratio: the optimal C:N ratio of the raw materials is between 25:1 and 30:1, though 20:1 to 40:1 is acceptable. Finished compost should reach about 10:1 to 15:1. Straw and dry leaves are rich in carbon; dung, urine and green material supply nitrogen.
• Moisture: materials should hold 40 to 65 per cent moisture, ideally starting at 50 to 60 per cent and finishing at about 30 per cent.
• Air: aerobic composting needs oxygen. Where oxygen is short, aerobic micro-organisms are limited and decomposition slows.
• Temperature: the first stage works best at 20 to 45 degrees Celsius, after which heat-loving organisms work at 50 to 70 degrees. Pathogens are destroyed at 55 degrees and above, and the critical point for killing weed seeds is 62 degrees.
• pH: should not exceed 8, because at higher pH more ammonia gas is given off and nitrogen is lost.

FAO describes how a well-built heap behaves. In the heating phase its temperature rises rapidly, to 70 to 80 degrees within the first couple of days. Later comes curing, when turning no longer reheats the pile, and finally maturation, when the material becomes dark brown to black. BARC adds that high temperature and high humidity favour rapid decomposition, which suits Bangladesh's climate.

BARC's Fertilizer Recommendation Guide-2024 gives a simple heap method that needs no pit. Its steps are these:

• Collect the raw materials (straw, leaves, weeds, water hyacinth, household waste and similar) and place them in layers, one above another. Each layer may be 25 to 30 cm thick.
• Keep the heap preferably 1.5 to 2.0 metres wide and not more than 1.5 metres high.
• To promote microbial activity, place a thin layer of soil or fresh cow dung, 4 to 5 cm thick, between the layers of material.
• Cover the top of the heap with soil.
• Keep the heap moist by spraying water at regular intervals.
• After one and a half to two months, reverse the layers into a new heap so that the material decomposes evenly.
• Depending on the weather and the materials used, the compost is ready in four to six months.

The guide offers two ways to speed things up. A microbial accelerator such as the fungus Trichoderma, if available, can be used for rapid composting; the product is called trichocompost. Earthworms can also do the work: they convert manure and household refuse into vermicompost, and are especially efficient at breaking down tough wastes such as sugarcane trash. Epigeic, surface-living worms are the most widely used, and BARC names Eisenia fetida (the red wiggler or tiger worm) as the species most often used, followed by Eisenia andrei, Eudrilus eugeniae and Lumbricus rubellis.

FAO's manual adds advice on the site. The heap or pit should be at a level high enough to keep rainwater out, near the cattle shed and a water source, with shade for some methods, and on a sloping floor so that it does not become waterlogged.

Many farmers prefer a pit, which holds moisture and is easier to manage in strong sun. TNAU's portal describes farm compost made in trenches 4.5 to 5.0 metres long, 1.5 to 2.0 metres wide and 1.0 to 2.0 metres deep. The farm waste is placed in layers, each moistened with cow dung slurry or water, and the trench is filled to 0.5 metres above the ground. The compost is ready in five to six months.

TNAU says the nutrient value of farm compost can be increased by adding superphosphate or rock phosphate at 10 to 15 kg per tonne of raw material at the initial stage of filling the pit. Three methods developed in India are widely described.

FAO credits the Indore method to Sir Albert Howard, who developed it at Indore, India, in the mid-1920s. It uses mixed plant residues, animal dung and urine, earth, wood ash and water. In FAO's description, the pit is about 1 metre deep, 1.5 to 2 metres wide and of a suitable length. Material from the cattle shed is spread in even layers of 10 to 15 cm, and a slurry of 4.5 kg of dung, 3.5 kg of urine-soaked earth and 4.5 kg of inoculum from a 15-day-old composting pit is spread on each layer. The material is turned three times: 15 days after filling, after another 15 days, and after another month. The process takes about three to four months.

TNAU describes a cattle-shed version. Organic waste is spread as bedding in the shed. Each day the urine-soaked bedding and dung are removed and laid in a 15 cm layer at a chosen site. Urine-soaked earth from the shed is mixed with water and sprinkled on the layer two or three times a day for about a fortnight. A thin layer of good compost is then spread on top and the mass is turned; the old compost helps start decomposition. After about a month the material is moistened and turned again, and it is ready about a month later.

FAO dates the Bangalore method to 1939 in Bangalore, India. In TNAU's description, dry waste is spread 25 cm thick in a pit and a suspension of cow dung in water is sprinkled over it for moistening. Layers of dry waste and dung suspension alternate until the pit is filled to 0.5 metres above the ground. It is left exposed for 15 days, then turned, plastered with mud and left undisturbed for about five months, or until needed.

FAO notes that after an initial aerobic phase of about eight to ten days the material decomposes anaerobically at a slow rate, so the method takes about six to eight months. Its advantages are protection from weather and from nutrient loss to wind and sun, no frequent turning, and fewer flies.

TNAU describes the Coimbatore method, named after the city in Tamil Nadu. The pit size varies with the waste available. A layer of waste is laid in the pit and moistened with a suspension of 5 to 10 kg of cow dung in 2.5 to 5.0 litres of water, and 0.5 to 1.0 kg of fine bone meal is sprinkled over it evenly. Layers are added until the material stands 0.75 metres above the ground. The heap is plastered with mud and left undisturbed for 8 to 10 weeks. It is then taken out, moistened, turned into a rectangular heap and kept in the shade until used.

In the Coimbatore method, TNAU says, decomposition starts anaerobic and is followed by aerobic fermentation. It is the reverse in the Bangalore method, which starts aerobic and then becomes anaerobic.

Wherever animals are kept, there is waste. Bangladesh's livestock numbers make the scale clear. The Department of Livestock Services (DLS) put the 2023-24 population, from Bangladesh Bureau of Statistics figures, at 250.13 lakh cattle, 15.24 lakh buffaloes, 39.03 lakh sheep and 271.17 lakh goats, along with 3,277.77 lakh chickens and 682.61 lakh ducks.

Where animals are kept in sheds rather than grazed, their dung and urine must be collected, moved and stored, and each step can harm the environment if done carelessly. BARC warns that substantial quantities of animal manure and its nutrients are lost through careless handling. Its advice is to store manure in pits under shade, to keep the nitrogen-rich cattle urine with the dung, and to keep the manure moist to reduce the loss of nitrogen as gas. Animal manure generally takes two to three months to decompose, and fresh manure should not be applied to standing crops, because the heat and carbon dioxide released during vigorous decomposition harm young roots.

Badly managed manure also pollutes the air. FAO's 2006 report Livestock's Long Shadow estimated that livestock were responsible for almost two-thirds (64 per cent) of human-caused ammonia emissions, which contribute significantly to acid rain and the acidification of ecosystems, and for 65 per cent of human-caused nitrous oxide, the great majority of it from manure. Composting and covered storage keep more of that nitrogen in the manure, where it can feed crops.

A biogas plant is another route. BARC describes bio-slurry, the manure that comes out of a biogas digester after the gas, chiefly methane, is extracted, and says it keeps the fertiliser value of the original dung. Its pit should be shaded from sun and rain; the main difficulty is carrying it to distant fields.

BARC's guide notes that the government approved a standard specification for organic fertiliser through a Ministry of Agriculture gazette notification on 2 April 2008. Under it, organic fertiliser should be non-granular, dark grey to black in colour, and free of bad smell. Good organic fertiliser does not form clods when pressed in the hand. These checks give a first idea of quality, but the guide stresses that quality can only be confirmed by laboratory analysis.

The same guide lists the maximum toxic metal content allowed in organic fertiliser: 20 ppm arsenic, 5 ppm cadmium, 30 ppm lead, 0.1 ppm mercury, 50 ppm chromium and 30 ppm nickel, with 0.1 per cent zinc and 0.05 per cent copper. This is why municipal and leather wastes must be treated before they go into compost.

When compost, cow dung, poultry manure or bio-slurry is used, BARC advises adjusting the chemical fertiliser rates for the nutrients the manure supplies, counting on 50 per cent of them being mineralised for the crop. BARC's per-tonne supply figures given above already take this mineralisation into account. It also advises applying a small amount of cow dung, compost or poultry litter before planting most crops.

For help with the right rate for a field, the materials to use and soil testing, farmers can contact the Sub-Assistant Agriculture Officer of their union or the Upazila Agriculture Office of the Department of Agricultural Extension (DAE), and the regional laboratories of the Soil Resource Development Institute (SRDI).

Photo: Sindugab / Wikimedia Commons (CC BY-SA 4.0)

Sources: The Agro News (Staff Correspondent), Bangladesh Agricultural Research Council (Fertilizer Recommendation Guide-2024), Tamil Nadu Agricultural University Agritech Portal, Food and Agriculture Organization of the United Nations (On-farm composting methods, 2003; Livestock's Long Shadow, 2006), Department of Livestock Services (Livestock Economy at a Glance 2023-2024)