How to Use Pig Manure as Fertilizer: Composting Ratios

Pig manure is the most nutrient-dense livestock manure available to a small farmer - roughly 2-3 times richer in nitrogen than cattle manure and 4-5 times richer than poultry. But raw pig manure is a problem, not a resource. It burns plant roots with excess ammonia, introduces pathogens (E. coli, salmonella, parasites) to your soil, smells terrible, and attracts flies. Properly composted, it becomes "black gold" - a stable, pathogen-free, slow-release fertilizer worth 200,000+ FCFA per year for a 20-sow operation. This article is the exact process, ratios, and economics.

Why you cannot apply raw pig manure directly

Raw pig manure contains:

• Excess nitrogen as ammonia (NH3): ammonia is toxic to plant roots at concentrations above 100ppm. Fresh pig manure can have 5,000-15,000ppm. Apply it raw and you chemically burn your crop.
• Pathogens: salmonella, E. coli, campylobacter, and parasite eggs (ascarids, whipworms). These survive in soil for months. Vegetables grown with raw manure can transmit them to humans.
• Volatile odor compounds: hydrogen sulfide, ammonia, volatile fatty acids. These attract flies for kilometers around and create conflict with neighbors.
• Phytotoxic compounds: uric acid and certain organic acids inhibit seed germination.
• Excess water (80-90% moisture): raw manure is heavy, hard to transport, and creates anaerobic conditions if piled (which produces more odor and pathogens).

Composting solves all 5 problems: it converts ammonia to stable organic nitrogen, kills pathogens with heat (55+ degrees C for 3+ weeks), eliminates odor through aerobic decomposition, breaks down phytotoxins, and reduces moisture to 30-40 percent (making it crumbly and easy to handle).

The carbon-to-nitrogen (C:N) ratio - the most important number

Composting is a microbial process. Microbes need a balanced diet of carbon (for energy) and nitrogen (for protein). The ideal C:N ratio for composting is 25-30:1. Pig manure alone is 6-10:1 (too much nitrogen - the excess volatilizes as ammonia and the pile smells bad). You must mix it with a carbon source to reach the target ratio.

Common carbon sources and their C:N ratios:

• Sawdust: 400-500:1
• Straw (cereal): 80-100:1
• Dry maize stalks: 60-80:1
• Banana leaves (chopped): 30-40:1
• Cassava peel (dried): 35-45:1
• Paper/cardboard (shredded): 200-300:1
• Wood ash: not a carbon source, but adds potassium and raises pH

The exact mixing ratio

For every 1kg of fresh pig manure, add:

• 0.5-0.7kg of sawdust (gives a C:N of about 28:1) - this is the easiest ratio and sawdust absorbs excess moisture.
• OR 1.5-2kg of chopped dry straw (lower C:N means you need more by weight).
• OR 1.5kg of chopped dry maize stalks.

If you have access to sawdust from a local sawmill, it is almost always the best choice - it is usually free or very cheap, it absorbs the 80 percent moisture of the manure, and the high C:N ratio means you need relatively little by weight.

The 6-week composting process

Here is the week-by-week process. Build the pile at least 1m x 1m x 1m (smaller piles do not heat up enough to kill pathogens).

Week 1: Build the pile. Layer pig manure and carbon source in a 2:1 ratio by volume (about 1:0.5 by weight if using sawdust). Wet the pile lightly if dry (target moisture: 50-60 percent, like a wrung-out sponge). Cover with a thin layer of soil or leaves to retain heat and moisture.

Week 2: First turn. By day 7, the pile should have heated to 55-65 degrees C internally. If not, the pile is too dry, too wet, or the C:N ratio is off. Turn the pile thoroughly with a fork - move the outside to the inside, top to bottom. Re-wet if dry.

Week 3-4: Sustained heat. The pile should remain at 50+ degrees C for at least 3 weeks. This temperature kills pathogens, weed seeds, and parasite eggs. Turn every 5-7 days to maintain oxygen supply (without oxygen, the pile goes anaerobic and smells bad).

Week 5: Cooling. The microbial activity slows, the pile cools to 30-40 degrees C. The material is now dark brown and earthy-smelling. Turn once more and let cure.

Week 6: Cure and apply. The compost should be dark, crumbly, sweet-smelling (like forest soil), and have no recognizable manure pieces. It is now safe to apply to any crop, including vegetables for human consumption. Apply at 2-5 tons per hectare depending on soil fertility.

The economics: how much money you save

A 20-sow operation with 200 growing pigs produces approximately 5 tons of fresh manure per month, or 60 tons per year. Composted at a 2:1 manure-to-sawdust ratio, this yields 30-35 tons of finished compost per year.

Compost market value: 5,000-8,000 FCFA (~$13.3) per ton (bulk price to vegetable farmers and crop farmers). Even if you use the compost on your own fields (saving the cost of buying NPK fertilizer), the value is 7,000-10,000 FCFA (~$16.7) per ton in saved input costs.

Annual value: 30 tons x 7,000 FCFA (~$11.7) = 210,000 FCFA (~$350) per year from a 20-sow operation. Plus you avoid disposal costs (or fines if your operation is causing pollution complaints).

If you have access to land to grow vegetables or maize, using your own compost to grow your own pig feed (cassava, maize, soybean) creates a closed-loop system: feed → pigs → manure → compost → crops → feed. This is how integrated farms achieve feed costs 30-40 percent lower than operations buying all feed externally.

The 5 mistakes that ruin compost

• Pile too small: piles under 1m x 1m x 1m never reach the temperature needed to kill pathogens. Build big.
• Pile too wet: soggy piles go anaerobic and stink. Add more carbon material. Target: squeeze a handful - it should feel like a wrung-out sponge, not drip water.
• Pile too dry: dry piles do not heat up. Water gently if needed.
• Never turning: without oxygen, no heat, no pathogen kill, just smelly rotting. Turn every 5-7 days minimum.
• Adding fresh manure to finished compost: re-contaminates it. Keep fresh manure and finished compost in separate piles.

Application: how to use the finished compost

Compost is a soil amendment, not a substitute for planting fertilizer. Apply it 2-4 weeks before planting so the nutrients begin mineralizing into plant-available forms. Recommended rates by crop:

• Maize: 5 tons/hectare broadcast before plowing
• Vegetables (tomato, pepper, cabbage): 10 tons/hectare, or 1 handful per planting hole
• Cassava: 3 tons/hectare (cassava is less demanding)
• Tree crops (palm, mango, citrus): 20-30kg per mature tree, applied around the drip line
• Fodder grass (Napier, Brachiaria): 8 tons/hectare after each cut

Never apply compost to very young seedlings - the soluble salts can burn tender roots. Apply after the plant has 4 true leaves.

Liquid manure: the bonus fertilizer

If your pig pens have a slatted floor and the manure washes into a collection pit, you have a second valuable fertilizer source: liquid manure. Dilute pig urine and slurry 1:5 with water and apply immediately to growing crops (within 24 hours - the nitrogen volatilizes fast). This is a fast-acting nitrogen fertilizer, perfect for leafy vegetables. Use cautiously: undiluted liquid manure will burn crops. Always test on a small area first.

A simple 200L drum set up as a liquid manure tank, with a tap at the bottom and a removable lid, costs 15,000 FCFA (~$25.0) and turns a waste product into a liquid fertilizer worth another 50,000-100,000 FCFA (~$167) per year.

Sources & References

• [1] Pig manure nutrient content and C:N ratio (6-10:1) verified by FAO Animal Waste Management Guidelines and academic literature. Source: https://www.fao.org
• [2] Composting temperatures (55-65°C) for pathogen kill verified by WHO and EPA composting standards. Source: https://www.who.int
• [3] Cameroon compost market value estimated from local agricultural input market reports. Source: https://www.espaceagro.com