Animal Manure
Part of Fertilizers & Soil Amendments
Types and application rates of animal manure — the most important and accessible fertilizer.
Why This Matters
Animal manure has been the foundation of agriculture for 10,000 years. Before synthetic fertilizers existed, every productive farm in the world relied on animal waste to maintain soil fertility. In a rebuilding scenario, synthetic fertilizers will be among the first industrial products to disappear, and manure will once again become the single most important input for food production.
Manure is not just a nitrogen source — it is a complete soil amendment. It provides all three major plant nutrients (nitrogen, phosphorus, potassium), dozens of micronutrients, organic matter that improves soil structure, and a thriving community of beneficial microorganisms. No other single material does all of this simultaneously.
Understanding the differences between manure types is critical because not all manure is equal. Chicken manure is roughly 10 times more concentrated in nitrogen than cow manure. Applying chicken manure at cow-manure rates will burn and kill your crops. Applying cow manure at chicken-manure rates will leave your soil starving. The details matter.
Nutrient Content by Animal
Comparative Analysis
All values are approximate percentages of fresh (wet) manure. Actual values vary significantly based on animal diet, bedding material, and storage conditions.
| Animal | Nitrogen (N) | Phosphorus (P2O5) | Potassium (K2O) | Moisture | C:N Ratio |
|---|---|---|---|---|---|
| Chicken (layer) | 1.5-2.0% | 1.5-1.8% | 0.8-1.0% | 75% | 7:1 |
| Chicken (broiler) | 2.0-3.0% | 1.8-2.5% | 1.5-2.0% | 25-40% | 10:1 |
| Horse | 0.5-0.7% | 0.3-0.4% | 0.5-0.6% | 60-70% | 25:1 |
| Cow (dairy) | 0.5-0.6% | 0.2-0.3% | 0.5-0.6% | 85% | 18:1 |
| Cow (beef) | 0.6-0.7% | 0.3-0.4% | 0.5-0.7% | 80% | 20:1 |
| Pig | 0.6-0.8% | 0.5-0.7% | 0.4-0.5% | 75% | 14:1 |
| Sheep/Goat | 0.9-1.2% | 0.5-0.6% | 0.8-1.0% | 65% | 16:1 |
| Rabbit | 2.0-2.5% | 1.3-1.5% | 0.5-0.6% | 45% | 8:1 |
| Pigeon/Dove | 4.0-5.0% | 2.0-2.5% | 1.0-1.5% | 50% | 5:1 |
Key Observations
Hot manures (high nitrogen, low C:N ratio): Chicken, rabbit, pigeon. These will burn plants if applied fresh. They decompose rapidly and release nutrients quickly. Must be composted or aged before application.
Cool manures (moderate nitrogen, higher C:N ratio): Cow, horse. These can be applied fresh in many situations without burning crops, especially if incorporated into soil before planting. They decompose slowly and release nutrients gradually over the growing season.
Sheep and goat manure falls in between — moderately hot, easy to handle (small, dry pellets), and well-balanced in nutrients.
Application Rates
General Guidelines
The right application rate depends on the crop, the manure type, and the soil’s existing fertility. As a starting point:
| Manure Type | Application Rate (fresh) | Application Rate (composted) |
|---|---|---|
| Chicken | 2-4 tonnes/hectare | 4-8 tonnes/hectare |
| Horse | 15-25 tonnes/hectare | 10-15 tonnes/hectare |
| Cow | 20-30 tonnes/hectare | 15-20 tonnes/hectare |
| Pig | 10-20 tonnes/hectare | 8-15 tonnes/hectare |
| Sheep/Goat | 8-15 tonnes/hectare | 6-10 tonnes/hectare |
| Rabbit | 3-5 tonnes/hectare | 5-8 tonnes/hectare |
In practical terms (for garden-scale application):
- Cow or horse manure: 5-8 cm layer spread over the bed and dug in (roughly 1 wheelbarrow per 3-4 square meters)
- Chicken or rabbit manure: 1-2 cm layer spread thinly (roughly 1 wheelbarrow per 10-15 square meters)
- Sheep/goat pellets: 2-3 cm layer scattered and raked in
Over-Application
More is not better. Excessive manure application causes: (1) nitrogen burn — roots are damaged by excess ammonia, leaves yellow and wilt; (2) phosphorus overload — accumulates in soil and can reach toxic levels for some plants; (3) salt buildup — manure contains salts that dehydrate roots at high concentrations; (4) water contamination — excess nutrients leach into groundwater and streams.
Crop-Specific Recommendations
| Crop Type | Preferred Manure | Timing | Notes |
|---|---|---|---|
| Leafy greens (lettuce, spinach) | Composted cow/horse | 2-4 weeks before planting | Light feeders, sensitive to burn |
| Brassicas (cabbage, broccoli) | Composted chicken or cow | At planting | Heavy feeders, need plenty of N |
| Root crops (carrots, beets) | Well-aged cow/horse | Previous fall | Fresh manure causes forked roots |
| Tomatoes, peppers | Composted any type | At planting + side-dress | Heavy feeders through season |
| Legumes (beans, peas) | Light cow/horse or none | At planting | Fix own nitrogen; excess N reduces yield |
| Corn/maize | Composted chicken or cow | At planting + side-dress | Very heavy nitrogen demand |
| Fruit trees | Composted any type | Fall or early spring | Ring application around drip line |
Fresh vs. Composted Manure
Why Composting Matters
Fresh manure has several problems that composting solves:
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Pathogen risk: Fresh manure contains bacteria (E. coli, Salmonella), parasites (roundworms, tapeworms), and other pathogens. Composting at temperatures above 55°C for 3+ days kills virtually all pathogens.
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Nitrogen volatilization: Fresh manure releases ammonia gas, wasting nitrogen into the atmosphere. Composting stabilizes nitrogen in organic forms that release slowly into soil.
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Weed seeds: Animals eat seeds, and many survive digestion intact. Hot composting (above 55°C) kills weed seeds. Unprocessed manure can introduce massive weed problems.
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Burn risk: High-nitrogen fresh manure (chicken, rabbit) generates ammonia and heat that can damage or kill plant roots.
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Handling: Composted manure is drier, lighter, odorless, and easier to spread than fresh manure.
When Fresh Manure Is Acceptable
Fresh cow or horse manure can be applied directly in these situations:
- Fall application: Spread on beds that will not be planted for 3-4 months. Winter weather breaks it down.
- Top-dressing established orchards: Applied around (not touching) tree trunks. Distance and time allow safe nutrient release.
- Green manure incorporation: Tilled into soil with a cover crop, at least 4 weeks before planting the next crop.
The 120-Day Rule
As a food safety practice, allow at least 120 days between fresh manure application and harvest of any crop where the edible portion contacts the soil (root crops, lettuce, strawberries). For crops where the edible portion does not contact soil (corn, tomatoes, tree fruit), 90 days is sufficient.
Composting Manure
Hot Composting Method
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Build the pile: Mix manure with carbon-rich material (straw, leaves, wood shavings) at a ratio of roughly 1 part manure to 2-3 parts carbon material (by volume). The pile should be at least 1 cubic meter (1m x 1m x 1m) to generate sufficient heat.
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Moisten: The pile should be as damp as a wrung-out sponge — moist throughout but not dripping.
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Wait for heat: Within 2-3 days, the pile interior should reach 55-70°C. Check by inserting a metal rod — it should feel hot to the touch when withdrawn.
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Turn the pile: After 5-7 days, fork the pile over so that outer material goes to the center. This ensures all material reaches pathogen-killing temperatures.
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Repeat turning: Turn every 5-7 days for a total of 3-4 turns over 3-5 weeks.
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Cure: After the pile no longer reheats after turning, leave it to cure for an additional 2-4 weeks. This allows the microbial community to stabilize.
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Finished compost: Dark, crumbly, earthy-smelling material with no recognizable manure texture. Ready for application.
Cold Composting (Aging)
Simply pile manure and wait. Over 6-12 months, natural decomposition converts it to a usable product. This is easier than hot composting but:
- Does not kill all pathogens
- Does not kill weed seeds
- Loses more nitrogen to the atmosphere
- Takes much longer
For low-risk manures (cow, horse) from healthy animals, cold composting is often adequate.
Special Considerations
Human Waste (Humanure)
Human waste is a valid fertilizer but carries the highest pathogen risk. If used:
- Hot-compost for a minimum of 1 year (not the standard 3-5 weeks)
- Ensure temperatures exceed 55°C for extended periods
- Apply only to non-food crops (orchards, timber, fiber) or to food crops with at least 1 year between application and harvest
- Never apply to crops eaten raw (salads, root vegetables)
Manure Tea (Liquid Fertilizer)
A quick-release liquid fertilizer:
- Fill a cloth bag or porous container with composted manure
- Submerge in a barrel of water (ratio: 1 part manure to 5-10 parts water)
- Steep for 3-7 days, stirring occasionally
- Use the liquid to water plants — dilute further (1:2 with water) if the color is darker than weak tea
- Apply every 1-2 weeks during the growing season
Manure tea provides immediately available nutrients for fast-growing crops and is especially valuable for container gardens and transplants.
Storing Manure
If you cannot compost or apply manure immediately:
- Cover piles with a tarp or thatch to prevent rain from leaching nutrients
- Store on a non-porous surface (compacted clay, concrete) if possible, to prevent nutrient runoff
- Keep away from water sources — a minimum of 30 meters from wells, streams, or ponds
- Turn stored manure periodically to prevent anaerobic decomposition (which produces methane and foul odors)
Maximizing Manure Value
Bedding Matters
The bedding material mixed with manure significantly affects its value:
- Straw: Excellent — high carbon, absorbs urine (capturing nitrogen), decomposes to quality humus
- Wood shavings: Good — high carbon, slow to decompose, very absorbent
- Sawdust: Acceptable — very high carbon, may temporarily tie up soil nitrogen during decomposition
- Sand: Poor — adds no carbon, makes manure heavy and difficult to spread
Urine Capture
Animal urine contains approximately half the nitrogen and most of the potassium excreted by livestock. Bedding that absorbs urine (straw, shavings) captures these nutrients. Slatted floors that let urine drain away waste valuable fertilizer. Design animal housing to maximize urine capture in absorbent bedding material.
Integration with Crop Rotation
The most efficient system cycles nutrients continuously:
- Animals graze on pasture or are fed crop residues
- Manure (with bedding) is collected from housing areas
- Manure is composted
- Compost is applied to cropland
- Crops feed humans and animals
- Residues return to animals or compost pile
This closed loop minimizes nutrient loss and maintains soil fertility indefinitely — it is how agriculture functioned for millennia before synthetic fertilizers.