Animal Manure
Part of Soil Science
Animal manure is the most accessible concentrated fertilizer in a pre-industrial society, providing nitrogen, phosphorus, potassium, and organic matter that rebuilds soil structure and feeds the microbial life essential to plant growth.
Before synthetic fertilizers, every successful agricultural society was built on manure. A single cow produces 10-15 tonnes of manure per year — enough to fertilize half a hectare of cropland. Manure provides the three primary plant nutrients (nitrogen, phosphorus, potassium), essential micronutrients, and the organic matter that transforms dead mineral soil into a living, productive growing medium. But manure is not a simple “more is better” input. Applied incorrectly, it burns plants, contaminates water, introduces pathogens, and wastes nutrients to the atmosphere. Understanding what manure contains, how to process it, and when to apply it separates productive farming from environmental damage.
Nutrient Content by Animal
Different animals produce manure with different nutrient profiles. The values below are for fresh manure including urine, which contains a significant portion of the total nitrogen and potassium.
NPK Comparison (Fresh Manure, per tonne)
| Animal | Nitrogen (N) kg | Phosphorus (P2O5) kg | Potassium (K2O) kg | Moisture % | C:N Ratio | Annual Output (kg) |
|---|---|---|---|---|---|---|
| Chicken | 10-15 | 8-12 | 4-6 | 75 | 7:1 | 40-60 per bird |
| Sheep | 7-10 | 3-5 | 8-12 | 65 | 16:1 | 600-800 |
| Pig | 5-7 | 3-5 | 4-6 | 80 | 14:1 | 1,500-2,000 |
| Horse | 5-7 | 2-3 | 5-7 | 70 | 25:1 | 8,000-10,000 |
| Cow | 4-6 | 2-3 | 4-6 | 85 | 18:1 | 10,000-15,000 |
| Rabbit | 10-12 | 8-10 | 3-5 | 60 | 8:1 | 50-70 per animal |
| Goat | 7-10 | 3-5 | 8-12 | 65 | 16:1 | 500-700 |
Chicken and Rabbit Manure Are the Strongest
Chicken and rabbit manure contain 2-3 times more nitrogen per tonne than cow or horse manure. This makes them the most efficient fertilizers per unit weight — but also the most dangerous to use fresh. Fresh chicken manure applied directly to growing plants will burn roots and foliage within days. Always compost chicken and rabbit manure before application, or apply in fall with 4-6 months before planting.
Understanding the Numbers
Nitrogen (N): Drives leaf and stem growth. The most volatile nutrient — easily lost to the atmosphere as ammonia gas or leached below the root zone by rain. Fresh manure nitrogen is partly in ammonia form (immediately available but easily lost) and partly in organic form (slowly released by microbial breakdown over weeks to months).
Phosphorus (P2O5): Drives root development, flowering, and seed formation. Relatively stable in soil — does not leach easily. Manure is one of the best phosphorus sources because the organic matter helps keep phosphorus in plant-available forms.
Potassium (K2O): Drives overall plant health, disease resistance, and fruit quality. Moderately mobile in soil. Manure potassium is immediately available to plants.
Fresh vs Composted Manure
The single most important decision in manure management is whether to apply it fresh or composted. Each approach has distinct advantages and risks.
Fresh Manure
| Advantage | Disadvantage |
|---|---|
| Higher total nitrogen content | Ammonia volatilization (nitrogen lost to air) |
| Immediate nutrient availability | Plant burn risk from ammonia |
| No composting labor required | Weed seeds remain viable |
| Pathogen risk (E. coli, Salmonella, parasites) | |
| Odor attracts flies and pests | |
| Nitrogen leaching risk in rain |
When to use fresh: Apply in fall, at least 90 days before spring planting (120 days for root crops and leafy greens that contact soil). This gives time for ammonia to dissipate, pathogens to die, and organic nitrogen to begin mineralizing. Incorporate into soil immediately after spreading — surface-applied fresh manure loses 50-80% of its nitrogen to the atmosphere within 48 hours.
Fresh Manure and Food Safety
Fresh manure contains E. coli, Salmonella, Campylobacter, and parasitic organisms (roundworm eggs, Cryptosporidium, Giardia). These pathogens can survive in soil for weeks to months. NEVER apply fresh manure to actively growing food crops, especially those eaten raw (lettuce, carrots, radishes, herbs). The minimum safe interval between fresh manure application and harvest is 120 days for crops with edible portions contacting soil, and 90 days for crops not contacting soil. Composting at proper temperatures eliminates this risk.
Composted Manure
| Advantage | Disadvantage |
|---|---|
| Pathogens killed by composting heat | 30-50% of nitrogen lost during composting |
| Weed seeds killed above 55 degrees C | Requires 2-4 months of composting |
| Stable, slow-release nutrients | Labor for turning and monitoring |
| No plant burn risk | Needs carbon source (bedding/straw) |
| Improves soil structure | Space for compost piles |
| Pleasant earthy smell |
Composting temperatures for pathogen kill:
| Temperature | Duration | Kills |
|---|---|---|
| 55 degrees C | 3 days | Most bacteria, many parasites |
| 60 degrees C | 3 days | All vegetative bacteria, most parasite eggs |
| 65 degrees C | 3 days | Virtually all pathogens and weed seeds |
| 70+ degrees C | Any | Complete sterilization (but kills beneficial organisms too) |
The Composting Temperature Sweet Spot
Aim for 55-65 degrees C sustained for at least 3 consecutive days. Reach this by building compost piles at least 1 cubic meter in volume with a carbon-to-nitrogen ratio of 25-30:1 (mix manure with straw, wood shavings, or dry leaves). Turn the pile when temperature drops below 50 degrees C, bringing outer material to the center. Three turns over 2-3 months produces finished compost safe for all applications.
Application Rates
More manure is not always better. Over-application wastes nutrients (excess leaches into groundwater), creates nutrient imbalances, and can accumulate salts and heavy metals in soil.
Recommended Annual Application Rates
| Crop Type | Composted Manure (tonnes/hectare) | Fresh Manure (tonnes/hectare) | Timing |
|---|---|---|---|
| Heavy feeders (corn, squash, cabbage) | 20-30 | 30-45 | Spring (composted) or fall (fresh) |
| Medium feeders (tomatoes, peppers, beans) | 10-20 | 15-30 | Spring (composted) or fall (fresh) |
| Light feeders (root crops, herbs) | 5-10 | 10-15 | Fall only (fresh) |
| Pasture/hay | 10-20 | 15-25 | Fall or early spring |
For small garden beds, a practical rule: spread composted manure 2-5 cm thick and incorporate into the top 15 cm of soil. For fresh manure in fall, spread 5-8 cm thick and dig in.
Matching Manure to Crops
| Manure Type | Best For | Avoid For | Reason |
|---|---|---|---|
| Chicken (composted) | Corn, squash, cabbage, heavy feeders | Seedbeds, root crops | Very high nitrogen, even composted |
| Cow | All crops, general amendment | None significant | Balanced, mild, hard to over-apply |
| Horse | All crops, especially clay soil improvement | Precision crops (many weed seeds) | Good structure, but weedy unless composted hot |
| Sheep/goat | Fruit trees, perennials | Quick-growing annuals (slow release) | Pellet form, slow breakdown |
| Rabbit | Container growing, seedbeds, side-dressing | None significant | Balanced, gentle, can use fresh |
| Pig | Corn, squash (after composting) | Root crops, leafy greens | Highest pathogen risk, always compost first |
Rabbit Manure Is the Exception
Rabbit manure is the only common livestock manure that can be safely applied directly to growing plants without composting. Its pellet form and relatively balanced nutrient profile release nutrients slowly without burning. It also has very low odor and does not attract flies. If you keep rabbits, their manure is the most convenient and safest garden fertilizer available.
Bedding as Carbon Source
Most manure is collected with bedding material — straw, wood shavings, sawdust, or hay used to absorb urine and provide comfortable footing in barns and coops. This bedding is not waste — it is an essential carbon source that makes manure compost properly.
Carbon-to-Nitrogen Ratios
Effective composting requires a carbon-to-nitrogen (C:N) ratio of 25-30:1. Most manure alone is too nitrogen-rich (low C:N), which causes ammonia loss and smelly, slimy composting. Bedding materials provide the carbon to balance the ratio.
| Material | C:N Ratio | Notes |
|---|---|---|
| Chicken manure (no bedding) | 7:1 | Far too nitrogen-rich alone |
| Cow manure (no bedding) | 18:1 | Slightly low in carbon |
| Straw | 80:1 | Excellent carbon source |
| Wood shavings | 300-500:1 | Very high carbon, use sparingly |
| Sawdust | 400:1 | Ties up nitrogen if not composted |
| Hay | 30:1 | Near-ideal for mixing with hot manure |
| Dry leaves | 50-80:1 | Good, free carbon source |
Mixing ratios for composting:
| Manure | Bedding | Approximate Ratio by Volume | Result C:N |
|---|---|---|---|
| Chicken | Straw | 1:3 | ~28:1 |
| Chicken | Wood shavings | 1:2 | ~30:1 |
| Cow | Straw | 1:1 | ~25:1 |
| Horse (with straw bedding) | Already mixed | As collected | ~25-30:1 |
| Pig | Straw | 1:2 | ~27:1 |
Manure Tea
A liquid fertilizer made by steeping manure in water. Provides a quick-acting nutrient boost for actively growing plants.
Preparation:
- Fill a permeable bag (burlap sack, cloth bag) with aged or composted manure — approximately 1 part manure to 5 parts water.
- Suspend the bag in a barrel or large container of water.
- Steep for 3-7 days, stirring daily.
- Remove the bag. The resulting brown liquid is ready to use.
- Dilute to the color of weak tea (approximately 1 part concentrate to 3-5 parts water) before application.
Application: Pour at the base of plants, not on foliage. Apply every 2-4 weeks during active growth. Best used as a supplement to solid manure applications, not a replacement.
Never Use Fresh Manure Tea on Food Crops
Manure tea made from fresh (uncomposted) manure carries the same pathogen risks as fresh manure. Use only well-composted manure for tea intended for food crops. For ornamental plants and fruit trees, fresh manure tea is acceptable if applied to soil only (not foliage).
Avoiding Over-Application
Excess manure causes real problems that take years to correct.
Signs of Over-Application
| Symptom | Cause | Solution |
|---|---|---|
| Dark green, lush foliage with poor fruiting | Excess nitrogen | Stop manure, grow heavy-feeding grain crop |
| White crust on soil surface | Salt accumulation | Irrigate to leach salts, reduce application |
| Plants wilt despite moist soil | Root burn from ammonia | Flush with water, stop fresh manure |
| Algae in nearby water bodies | Phosphorus runoff | Reduce application, establish buffer strips |
| Tomato/pepper blossom drop | Excess nitrogen pushes vegetative growth | Skip manure for 1-2 seasons |
Phosphorus Accumulation
Nitrogen is consumed or lost relatively quickly, but phosphorus accumulates in soil over years of manure application. After 5-10 years of regular manure use, phosphorus levels may become excessive while nitrogen still needs supplementation. At this point, switch to nitrogen-only inputs (legume cover crops, small amounts of blood meal) and reduce or stop manure application until phosphorus levels moderate.
Nutrient Runoff Prevention
Manure nutrients that enter waterways cause algal blooms, oxygen depletion, and fish kills. Prevention is both an environmental and practical concern — nutrients that run off are nutrients wasted.
Key prevention practices:
- Never apply manure to frozen or waterlogged soil (it cannot infiltrate and will wash off with the next rain)
- Never apply within 10 meters of any waterway, well, or spring
- Incorporate fresh manure into soil within 24 hours of application
- Do not apply more than the crop can use in one season
- Maintain vegetated buffer strips between manured fields and water
- Store manure piles on flat ground away from waterways, covered or under a roof to prevent rain from leaching nutrients
The Manure Pile Needs a Roof
An uncovered manure pile loses 30-60% of its nitrogen to rain leaching and volatilization. A simple roof structure (posts and a sloped panel of boards or thatch) over your compost/manure pile pays for itself many times over in preserved nutrient value. The investment is a few hours of construction; the return is measured in years of better fertility.
Seasonal Manure Management Calendar
| Season | Activity | Notes |
|---|---|---|
| Winter | Collect and stockpile manure with bedding | Store under cover, begin composting piles |
| Early Spring | Apply composted manure before planting | Incorporate into soil 2-3 weeks before planting |
| Late Spring | Side-dress heavy feeders with manure tea | Diluted composted manure tea only |
| Summer | Continue composting, turn piles regularly | Monitor temperature, maintain moisture |
| Early Fall | Apply fresh manure to empty beds | Incorporate immediately, 120+ days before harvest |
| Late Fall | Spread composted manure on perennial beds | Light application, 2-3 cm, as winter mulch |
Summary
Animal manure is the cornerstone of pre-industrial soil fertility. Chicken and rabbit manure are the most nutrient-dense (10-15 kg N per tonne), while cow and horse manure provide gentler, more balanced fertility with excellent soil structure improvement. Always compost manure before spring application — sustained temperatures of 55-65 degrees C for 3+ days kill pathogens and weed seeds. Fresh manure is safe only when applied in fall, at least 120 days before harvesting root crops or leafy greens. Mix manure with carbon-rich bedding (straw, leaves, wood shavings) at a C:N ratio of 25-30:1 for effective composting. Rabbit manure is uniquely safe for direct application to growing plants. Apply composted manure at 2-5 cm depth for garden beds, incorporated into the top 15 cm. Avoid over-application — excess nitrogen burns plants and excess phosphorus accumulates over years. Cover manure storage to prevent nutrient loss from rain, never apply to frozen soil or near waterways, and maintain buffer strips between manured land and water sources.