Grade 10 Agriculture Agricultural Technologies and Entrepreneurship – Composting Techniques Notes

Specific Learning Outcomes

• a) Describe composting methods in the production of organic manure
• b) Examine factors that influence the quality of compost manure
• c) Carry out conventional composting methods for production of organic manure
• d) Carry out innovative composting methods for production of organic manure
• e) Appreciate the role of composting in soil improvement

What is composting?

Composting is the controlled breakdown of organic materials (crop residues, kitchen waste, animal manure, leaves) by microbes into a dark, crumbly product called compost or organic manure. Compost adds nutrients and improves soil structure and water retention.

Materials commonly used in Kenya

• Green (nitrogen-rich): kitchen scraps (no meat), fresh grass, vegetable waste, manure (cow, goat, sheep).
• Brown (carbon-rich): dry maize stover, dry leaves, sawdust, sugarcane bagasse, paper/cardboard, wood ash (small amount).
• Bulking agents: topsoil (introduces microbes), wood chips, maize stalks to improve aeration.

Important factors affecting compost quality

• C:N ratio: Aim ~25–30:1 at start. Too high C (dry straw) slows down decomposition; too low C (fresh manure) can smell.
• Moisture: 40–60% ideal. Squeeze test: handful should feel like a wrung wet sponge (not dripping).
• Aeration: Oxygen is needed for aerobic microbes — turn piles or use bulking agents.
• Particle size: Smaller pieces decompose faster; chop or shred bulky materials.
• Temperature: Thermophilic stage (45–65°C) kills weeds and pathogens. Monitor with simple compost thermometer.
• pH: Compost usually works well at pH 6–8.
• Contaminants: Avoid plastics, meat, oils, diseased plant parts, herbicide residues.
• Time and management: Turning, moisture control and mixing determine how fast compost matures.

Conventional composting methods — how to do them (step-by-step)

1. Heap (Static heap)

1. Choose a shady, well-drained spot near water and a source of materials.
2. Lay down a 10–15 cm layer of coarse sticks/grass for drainage and air flow.
3. Build layers: brown (10 cm), green (5–10 cm), small layer of topsoil (1–2 cm) or manure to introduce microbes. Repeat until heap ~1–1.5 m high.
4. Keep moist (spray water). Cover with a mat or old sack if heavy rains are expected.
5. Turn the heap every 3–6 weeks to aerate (optional but speeds up process). Ready in 3–6 months.

2. Pit composting

1. Dig a pit 0.5–1 m deep (size based on material available).
2. Fill with alternating layers of brown and green, ending with soil on top.
3. Cover and leave for 6–12 months. Pit composting is good for small farms and homesteads.

3. Windrow (for larger quantities)

1. Form long rows (windrows) ~1–1.5 m high and 1–2 m wide.
2. Turn regularly (weekly or fortnightly) to keep aerobic — speeds up decomposition (2–4 months).

Innovative composting methods — how to do them

1. Vermicomposting (using worms)

1. Build or buy a bin (wooden box or plastic crate with holes for drainage).
2. Place bedding: shredded paper, dry leaves, soil and moisten to wrung-sponge level.
3. Add red worms (Eisenia fetida) — available from some nurseries or fellow farmers.
4. Add kitchen waste in small amounts, bury under bedding, avoid meat/dairy/citrus in excess.
5. Keep moist and in shade. Harvest worm castings in 2–3 months depending on load.

2. Bokashi (fermentation method)

1. Use an airtight bucket/bin and a bokashi mix (bran inoculated with EM/beneficial microbes).
2. Add kitchen waste in layers and sprinkle bokashi mix each layer; compress to remove air and seal.
3. Fermentation takes 2 weeks; then bury or compost the fermented material to finish decomposition — speeds up processing and handles cooked food.

3. Aerated Static Pile or In-vessel composting

• Forced air (pipes or blowers) provides oxygen without turning — used by large producers. Faster maturation, less labour.
• In-vessel systems (drums, tanks) control temperature and odor — suitable for entrepreneurs with capital.

Simple visual: compost heap cross-section

Checking compost maturity

• Looks dark and crumbly, earthy smell (not ammonia or rotten smell).
• No recognisable food or plant residues.
• Temperature near ambient (no longer hot).
• Germination test: plant radish/cress seeds in a pot with 30% compost mixed with soil — good compost gives high germination.

Role of composting in soil improvement and entrepreneurship

• Improves soil structure, porosity and water holding capacity — valuable in Kenya’s sandy soils and dry seasons.
• Supplies slow-release nutrients (N, P, K) and micronutrients; supports beneficial soil microbes.
• Reduces need for chemical fertilisers and lowers costs for smallholder farmers.
• Recycles farm and kitchen wastes and reduces pollution.
• Business opportunity: produce and sell compost or value-added products (enriched compost, compost tea, packaged compost). Markets: local farmers, nurseries, schools, floriculture and horticulture growers.

Suggested learning experiences (for age 15, Kenya)

• Practical: Build a school compost heap and a vermicompost bin. Keep a diary: materials, C:N estimate, moisture, temperature, turning dates and final yield.
• Measurement: Use a simple thermometer and moisture squeeze test weekly. Record temperature changes over time.
• Experiment: Make three small heaps with different C:N or moisture levels and compare time to maturity and smell.
• Field visit: Visit a local compost producer, county agriculture office or demo farm. Ask about markets and record costs.
• Project: Prepare a simple business plan to sell compost locally — include production costs, packaging, pricing, and marketing.
• Community action: Collect school kitchen waste and show how bokashi/vermicompost reduces waste and produces manure for school garden.

Safety and good practice

• Wear gloves when handling raw manure or very hot material.
• Wash hands after working with compost.
• Avoid adding diseased plant materials or meat/animal products.
• Keep composting site away from water sources to prevent contamination.