Nitrogen Sources

Part of Fertilizers & Soil Amendments

Nitrogen is the nutrient crops consume most voraciously and the one most likely to limit yields. Without industrial ammonia synthesis, you must find, concentrate, and manage natural nitrogen sources — the skills that separated thriving agricultural civilizations from those that starved.

Why Nitrogen Is the Limiting Factor

Nitrogen is the building block of proteins, chlorophyll, and DNA. A nitrogen-deficient plant is pale, stunted, and produces little food. While other nutrients matter, nitrogen is the one that runs out fastest because:

• Crops extract large quantities per harvest (a hectare of wheat removes roughly 50 kg of nitrogen annually)
• Nitrogen is mobile in soil — rain leaches it downward beyond root reach
• Soil microbes convert it to gas (denitrification) and it escapes to the atmosphere
• Unlike phosphorus or potassium, nitrogen does not accumulate from rock weathering

Without deliberate nitrogen management, agricultural soils decline within 3-5 years of continuous cropping.

Animal Manure

The most widely available and historically important nitrogen source. Every community with livestock has this resource.

Nitrogen Content by Animal

Manure Type	N Content (% fresh weight)	C:N Ratio	Best Application
Chicken/poultry	1.5-2.0%	7:1	Hot — compost before use
Rabbit	2.0-2.4%	8:1	Can apply directly
Horse	0.5-0.7%	25:1	Good composting base
Cow	0.3-0.5%	18:1	Gentle, good for all crops
Sheep/goat	0.7-1.0%	15:1	Good all-purpose
Pig	0.5-0.8%	12:1	High pathogen risk — compost first

Fresh poultry and pig manure can burn crops due to high ammonia content and carry harmful pathogens (E. coli, salmonella). Always compost these for at least 3 months before applying near food crops. Cow and horse manure are safer to apply fresh but still benefit from composting.

Collection and Storage

Maximize nitrogen retention during storage — nitrogen in manure is volatile and escapes as ammonia gas (the smell):

1. Collect daily — the longer manure sits exposed to air and sun, the more nitrogen evaporates
2. Mix with bedding (straw, sawdust) — carbon materials absorb and lock in nitrogen
3. Cover storage piles — a roof or tarp reduces rain leaching and ammonia loss
4. Keep moist but not wet — dry manure loses nitrogen to the air; soggy manure loses it to drainage water
5. Compact the pile — reducing air exposure slows ammonia volatilization

A covered manure pile retains 50-70% of its original nitrogen. An uncovered, rained-on pile retains only 15-25%. The simple act of covering your manure pile effectively doubles its fertilizer value.

Green Manure (Cover Crops)

Growing plants specifically to plow back into the soil. The most elegant nitrogen source because certain plants (legumes) pull nitrogen directly from the atmosphere.

Nitrogen-Fixing Legumes

Legumes host Rhizobium bacteria in root nodules. These bacteria convert atmospheric nitrogen gas (N2) into ammonia (NH3), which the plant uses for growth. When you turn the plant under, that nitrogen becomes available to the next crop.

Legume	N Fixed (kg/hectare/year)	Growth Season	Notes
Red clover	100-200	Perennial	Excellent for pasture rotation
White clover	50-150	Perennial	Low-growing, good understory
Crimson clover	70-150	Annual, cool season	Fast-growing winter cover
Hairy vetch	90-200	Annual, cool season	Vigorous, good weed suppression
Field peas	50-120	Annual, cool season	Also produces food
Soybeans	60-170	Annual, warm season	Dual-purpose: food + nitrogen
Fava beans	80-200	Annual, cool season	Handles cold well
Lupins	100-200	Annual	Tolerates poor, acidic soil
Alfalfa	150-300	Perennial (3-5 years)	Highest fixer, deep roots

How to Use Green Manure

1. Sow legume seed after harvest or in fallow rotation
2. Grow for at least 6-8 weeks (longer is better — more nitrogen fixed)
3. Cut at peak bloom, when nitrogen content is highest
4. Incorporate — chop and turn into the top 15 cm of soil
5. Wait 2-3 weeks before planting the next crop (allows decomposition to begin so nitrogen is released, not tied up)

Do not let green manure crops go to seed before incorporation. Once the plant shifts energy to seed production, nitrogen content in the leaves and stems drops significantly, and you get volunteer weeds the next season.

Human Waste (Humanure)

Taboo in modern contexts but historically one of the most important nitrogen sources. Chinese, Japanese, and Korean agriculture sustained enormous populations for millennia using “night soil.”

Safe Use Protocol

Human waste carries serious disease risks (cholera, typhoid, hepatitis, parasites). These are managed through proper composting:

1. Collect in a dedicated composting toilet — a simple chamber with carbon material (sawdust, leaves) added after each use
2. Compost for a minimum of 12 months at temperatures above 55°C for at least 3 days during the thermophilic phase
3. Apply only to fruit trees and perennial crops — never to root vegetables or leafy greens
4. Maintain a 6-month gap between application and harvest

If you cannot guarantee the compost reached 55°C+ for at least 3 days, extend the composting period to 24 months. Time alone kills most pathogens, but it takes much longer than heat. This is non-negotiable for food safety.

Nutrient Value

Human waste is rich in nitrogen (1.0-1.5% in feces, 15-18% in urine). Urine alone — diluted 10:1 with water — is a fast-acting nitrogen fertilizer that carries very low pathogen risk and can be applied directly to growing crops.

Urine as Fertilizer

Urine is perhaps the most underappreciated nitrogen source. It is sterile when fresh, immediately plant-available, and produced daily by every person.

Application

• Dilute 10:1 (water to urine) for direct application to growing plants
• Apply to soil, not to leaves — leaf contact can cause burning
• Apply in the morning — evening application increases slug attraction in some climates
• Weekly application during the growing season provides steady nitrogen

NPK Content

Fresh human urine contains approximately:

• Nitrogen: 6-8 g/liter
• Phosphorus: 0.5-1 g/liter
• Potassium: 1.5-2.5 g/liter

One adult produces roughly 500 liters of urine per year — enough nitrogen to fertilize about 300-400 square meters of vegetable garden.

Guano (Bat and Bird Droppings)

Where available, guano is one of the most concentrated natural nitrogen sources.

Types

Source	N Content	P Content	Availability
Fresh bat guano	10-12%	3-5%	Caves, abandoned buildings
Aged bat guano	2-4%	10-14%	Old cave deposits (more phosphorus, less N)
Seabird guano	10-16%	8-12%	Coastal cliffs, islands
Pigeon droppings	4-6%	2-3%	Dovecotes, abandoned structures

Harvesting

• Caves and cliff faces with bat or bird colonies accumulate deposits over years
• Scrape and collect dry material — avoid disturbing active nesting colonies
• Use as-is or compost briefly; guano is already well-decomposed
• Apply at rates of 0.5-1 kg per square meter for garden beds

If you find a significant guano deposit, ration it carefully. Guano deposits took centuries to accumulate and are a non-renewable resource on human timescales. Use sparingly on high-value crops.

Other Nitrogen Sources

Blood Meal

Blood collected from butchering, dried and crumbled. Contains 12-15% nitrogen. Apply as a side-dressing around growing plants at 100-200 g per square meter.

Feather Meal

Ground feathers from poultry processing. Contains 12-15% nitrogen but releases very slowly (3-6 months). Good for long-season crops.

Fish Scraps

Bury fish guts, bones, and heads 15-20 cm deep near crop plants. They decompose slowly, releasing nitrogen and phosphorus. The technique taught by Indigenous peoples to early European settlers in North America.

Nitrogen-Rich Weeds

Some weeds are nitrogen accumulators:

• Nettles — excellent nitrogen content; make into liquid fertilizer by soaking in water for 2 weeks
• Comfrey — deep taproots pull nutrients up from subsoil; cut and use as mulch or liquid feed
• Dandelions — moderate nitrogen; useful in compost

Common Mistakes

1. Applying too much nitrogen at once — excess nitrogen causes lush leaf growth but weak stems, pest vulnerability, and poor fruit/grain set. Apply in multiple small doses throughout the growing season.
2. Ignoring nitrogen losses — uncovered manure, broadcast urine, and exposed compost all lose nitrogen to the atmosphere. Cover, incorporate, and apply efficiently.
3. Relying on a single source — diversify nitrogen inputs. Green manure + animal manure + compost together build more resilient fertility than any one alone.
4. Skipping the legume rotation — legumes are the only way to add NEW nitrogen to the system from the atmosphere. Every rotation should include a legume crop or cover.
5. Using raw human waste on food crops — the disease risk is real and severe. Always compost properly for 12+ months.

Summary

Nitrogen Sources — At a Glance

• Nitrogen is the nutrient most likely to limit crop yields and must be actively managed
• Animal manure: cover storage piles to retain 50-70% of nitrogen; compost chicken and pig manure before use
• Green manure legumes fix 50-300 kg nitrogen per hectare per year from the atmosphere — the only way to add new nitrogen to the system
• Urine diluted 10:1 is a safe, immediate, free nitrogen fertilizer (one adult supplies 300-400 m2 of garden annually)
• Guano where available is 10-16% nitrogen but is non-renewable — use sparingly
• Compost humanure for at least 12 months with verified hot phase before applying to food crops
• Apply nitrogen in multiple small doses rather than one large application