Composting for Smallholder Agriculture: Turning Farm Waste into Soil Fertility

By: Lewis Kadzahlo

Why compost?

Every farmer generates waste (organic), from crop residues, manure, peels, and husks, and every farmer needs fertile soil. Composting is what turns one into the other: the controlled breakdown of organic matter by bacteria, fungi, and the soil food web into stable humus. Get the mix and airflow right, and it cleans up waste, kills weed seeds and disease, and rebuilds soil health. Get it wrong, and it collapses into a foul, slimy, airless mess.

About 5 per cent of a good topsoil is organic matter, and that is the only fraction a farmer can rebuild within a single cropping cycle[1]. Soils low in it cannot hold nutrients, and the chemical fertiliser you apply leaches away with the first heavy rain, a main reason fertiliser response on long-cropped Ghanaian fields has been falling. Compost also closes the nutrient loop: fertility exported as crops returns as compost made from your own organic waste, cutting dependence on imported NPK (nitrogen, phosphorus and potassium, the main plant nutrients) whose price swings with global shocks.

What you need: greens, browns and the Carbon to Nitrogen ratio (C:N) balance

The microbes that make compost need about 30 parts carbon to 1 part nitrogen, the C:N ratio. The best starting mix is 25 to 1 or 30 to 1, the one technical concept to remember [2], [3]. Below 20 to 1 the pile smells of ammonia. Above 40 to 11 it barely heats and stays immature for months.

• Greens are nitrogen-rich and wet: poultry manure, cattle dung, goat and sheep droppings, fresh grass, vegetable and fruit peels, market food waste, brewery spent grain. 
• Browns are carbon-rich and dry: maize stover (the workhorse brown for the Ghanaian compost yard), rice husk and straw, sorghum and millet stalks, dry leaves, cocoa pod husk after drying, palm fibre, and sawdust used sparingly. 
• With no lab data, use two to three parts browns by volume for every one part greens.

A working one-cubic-metre recipe is: cassava peel at 30 per cent of pile volume, chopped maize stover at 50 per cent, poultry litter at 15 per cent, and old compost or topsoil as inoculum (a living microbe starter) at 5 per cent. This gives a starting C:N near 28 to 1. Percentages are by volume and approximate, so verify locally.

Ghana generates these feedstocks in volume. Cocoa pod husk alone comes to more than 858,720 tonnes a year [4]. Cassava peels, rice husk, poultry litter across Brong Ahafo and Ashanti, cattle dung in the north, market food waste and sawdust are all there for the collecting.

One caution: fresh manure can carry pathogens and weed seeds. Always compost manure to 55 to 65 degrees Celsius for at least 15 days with regular turning before applying it to vegetable crops.

Building a heap or pit, step by step

1. Select well-drained, gently sloping ground, about 1 to 3 per cent slope. 

1. Avoid waterlogged depressions and floodplains. 
2. Keep at least 50 m from drinking-water wells or streams,
3. and 250 to 500 m from the nearest dwelling. 
4. Speak with the chief, assemblyman and elders before breaking ground, and verify locally with your District Assembly.

2. Select the method by your situation.

1. The heap, 2 to 5 m wide and 1.5 to 2 m high, is the simplest and most widely practised method in Ghana and suits farms and community gardens. 
2. The pit suits northern Ghana where moisture conservation is critical. 
3. The bin suits urban households, schools and peri-urban backyards.

3. Sorting; 

1. Keep a wet bin and a dry bin at the receiving pad. 
2. Remove plastics, glass, metals and agrochemical containers. 
3. Shred or chop bulky materials to 2 to 5 cm pieces, and have your bulking agents ready (rice husk, palm fibre, dry coconut husk, wood chips).

4. Build a starter pile of about 3 m by 2 m by 1.5 m, roughly 5 to 6 cubic metres fresh, will yield about 2 cubic metres of compost. 

1. Lay a 15 cm base of coarse twigs, palm fronds or maize stalks for aeration.
2. Add alternating 15 cm layers of chopped browns and 10 cm layers of greens, with a little old compost or topsoil as inoculum,
3. watering each lightly until damp but not dripping, until the pile reaches 1.5 m high. 
4. Build up, not out, because height drives self-heating. 
5. Cap with dry browns, cover loosely with palm fronds or a perforated tarpaulin that sheds rain but allows air, and insert a thermometer 60 cm into the centre. Start a logbook.

5. Avoid the common mistakes: building too small (under 1 cubic metre, so it will not heat), building too wide (over 3 m, so the centre cannot be reached for turning), using only one feedstock, adding too much water at once, and forgetting the base layer of coarse material.

Monitoring, troubleshooting and judging maturity

Composting moves through four stages: 

1. a mesophilic rise (day 0 to 7), 
2. a thermophilic phase (day 5 to 30, target 55 to 65 degrees Celsius, when pathogens and weed seeds are destroyed), 
3. cooling (weeks 4 to 8), and 
4. curing (weeks 6 to 16 and beyond). Do not skip curing, because immature compost can damage crops. 

For reliable pathogen kill, the public-health standard in Ghana is 55 to 65 degrees for at least 15 consecutive days [5], with at least five turns during that period, so every part of the pile passes through the hot core.

Check moisture with the hand-squeeze test: a handful squeezed from 30 cm into the pile should feel like a wrung-out sponge, with one or two drops, about 50 to 60 per cent. Too dry, add water and fresh greens. Too wet, above 65 per cent, turn and add dry browns. Turn when the core exceeds 65 degrees, falls below 40 degrees, or every 5 to 7 days in the active phase, whichever comes first, moving outer material to the hot centre of the new pile.

Troubleshooting is mostly reading the pile. Ammonia smell means too much nitrogen, so add browns and turn. A rotten-egg or sour smell means the pile has gone anaerobic, so turn, add dry browns and cover from rain. A pile that has not warmed after 5 to 7 days needs more greens, a larger rebuild if under 1 cubic metre, and a moisture check. Two signs of a healthy pile are core heat of 55 to 65 degrees and an earthy smell with visible decomposition. After active composting, cure the material at below 40 degrees for at least 4 to 8 weeks.

Judge maturity in the field without a laboratory: dark brown to black throughout, a crumbly soil-like texture, an earthy smell with no ammonia or sourness, and original feedstock no longer recognisable. As a check, a damp handful sealed in a bag for 24 hours should produce no foul odour. Keep a logbook from day one: pile ID, date built, feedstocks and volumes, moisture, turns, and core temperature readings.

Using compost on the farm

Apply compost 2 to 4 weeks before planting, and never just before heavy rain. Broadcast it for large fields, side-dress in rows next to growing plants (good for tomato and pepper), incorporate into the top 4 to 6 inches of soil to cut nitrogen loss, or mulch the surface in no-till systems. For soil improvement, apply 10 to 20 tonnes per acre to reclaim heavy clay or sandy soils. Only 10 to 30 per cent of compost nitrogen is mineralised in the first season, so compost is a slow-release amendment, not a quick green-up.

A maize crop in the Ashanti Region needs about 90 kg of nitrogen per hectare, but a tonne of compost supplies only about 3 kg in the first year. Meeting that from compost alone takes about 30 tonnes per hectare, which is high. So blend compost with a smaller dose of mineral nitrogen for the year-one crop, and let the soil improvement build over later seasons. The exact dose is not fixed in the sources, so verify locally with an extension officer.

Before bagging, confirm maturity, check moisture (35 to 45 per cent is ideal), and screen to size. Store in UV-stabilised bags with breather holes, on pallets in a cool, ventilated area, because heat above 50 degrees Celsius in storage kills beneficial microbes.

Across Ghana’s zones

Partial shade is ideal in southern Ghana to prevent the pile drying out. Full sun is acceptable in the dry savanna if the pile is covered. Site downwind of homes, schools and clinics.

The method shifts by zone. Heap composting suits the middle belt, where a manure-and-straw heap is common. Pit composting suits northern Ghana, where moisture conservation is critical, though it decomposes over 12 to 18 months due to limited aeration. Bin composting suits peri-urban households and school gardens.

Feedstocks shift by zone: cereal residues and cattle dung in the Northern, Upper East and Upper West Regions, poultry litter across Brong Ahafo and Ashanti, cocoa pod husk in the cocoa belt, and palm oil residues in the south.

The harmattan slows the process in the dry season, because lower humidity cuts microbial activity. Insulate the pile with extra browns and resume regular turning when humidity returns. In northern Ghana, where the rainy season is shorter and more intense, soil organic matter is a critical insurance policy, and the traditional parkland systems of shea, dawadawa and nere trees scattered through cropland are an indigenous agroforestry that has worked for centuries.

The Adom Senior High School project shows the principle in practice. One pit balanced food waste with dry leaves, was turned every three days, and stayed warm, earthy and alive. A second pit of mostly food waste, never turned and tightly sealed, went foul, slimy and cold.

Start small and scale up

Start a small pile while you study. Theory and practice must walk together, and the logbook belongs beside the compost pile from day one. Begin with one pile in the backyard, on the school plot, behind the shop or the church. Make every mistake this brief warns about and learn from each one. Build a second pile and a third. By the tenth pile you will be a competent practitioner, and by the hundredth you will be teaching others.

Composting rebuilds depleted soils, cleans up markets and lorry parks, creates jobs for young people, reduces the import bill for fertiliser, and is genuinely climate-smart. There is no waste. There is only material in the wrong place. Go and put it right.

References

1. Boincean, B. P., & Dent, D. L. (2019). Farming the black earth. Sustainable and Climate-Smart Management of Chernozem Soil. Spring Nature Switherland AG.
2. Azis, F. A., Choo, M., Suhaimi, H., & Abas, P. E. (2023). The effect of initial carbon to nitrogen ratio on kitchen waste composting maturity. Sustainability, 15(7), 6191.
3. Pavlis, R. (2023). Compost Science for Gardeners: Simple Methods for Nutrient-Rich Soil (Vol. 3). New Society Publishers.
4. Ayi, C. K. Cocoa Pod Husks (CPH) as a viable option for the production of Electricity in Ghana.https://site.unibo.it/saltafossi/it/articoli/sezione-fonti-rinnovabili-e-sostenibilita/eng-co-1.pdf/@@download/file/ENG-CO~1.PDF
5. World Health Organization. (2017). Joint external evaluation of IHR core capacities of the Republic of Ghana: mission report, 6-10 February 2017 (No. WHO/WHE/CPI/2017.26). World Health Organization.