Organic fertilizers are used to improve soil quality and tilth, and to provide nutrients for plant growth. They provide nitrogen, phosphorus, and potassium, as well as other elements essential for plant development and overall good health.
Nutrient values vary greatly among organic fertilizers. They also vary greatly for a given organic fertilizer. For example, as the table below shows, the nitrogen in raw bone meal ranges from 2 to 6%, and the phosphorus from 15 to 27%. Differences reflect variations in:
- the age of organic material
- its decomposition rate
- application method and timing
- incorporation time
- time exposed to the elements (rain, sun)
- the percentages of organic matter and water the material contains
- carbon-to-nitrogen ratio
- microbe population
- soil type.
Values for manures vary according to time of year, time in the open air, percentage of added straw, and rate of incorporation. The speed of release shown in the table indicates how quickly nutrients are made available to plants.
Some materials are regulated by Oregon Tilth. To be considered organic, they must result from organic farming methods. For example, cocoa shell meal and cottonseed meal must not be contaminated with pesticide residues. Raw manure is also regulated; composted manure is not. Wood ashes must not be from treated wood.
Nitrogen, phosphorus, and potassium are represented by N, P, and K in the table headings, to conform to standard commercial practice in labeling fertilizers. Phosphorus is actually present in the form of P2O5, potassium as K2O.
Top sources of nitrogen (N):
- Bat guano
- Blood/blood meal
- Crab waste
- Feather meal
- Fish meal (dry)
- Hair
- Hoof/horn meal
- Shrimp waste
Top sources of phosphorus (P):
- Bat guano
- Bone meal
- Crab waste
- Cucumber skins (burned)
- Hair
- Mushroom compost
- Phosphate
- Shrimp waste
Top sources of potassium (K):
- Crab waste
- Cucumber skins (burned)
- Granite (dust)
- Greensand
- Kaolinite (clay)
- Kelp
- Sulfate of potash magnesia
- Wood ashes
| Material | %N | %P | %K | Release Speed | Effectiveness | Comments |
|---|---|---|---|---|---|---|
| Alfalfa | 2.5 | 0.5 | 2 | Slow | 2 to 6 months | Cover crop |
| Animal Tankage (dry) | 7 | 10 | 0.5 | Medium | ||
| Bat Guano | 5.5 to 8 | 4 to 8.6 | 1.5 | Medium to fast | ||
| Bat Guano (Peruvian) | 12.3 | 8 to 11 | 2.5 | Medium | ||
| Blood (dried) | 12 | 1.5 | 0.6 | Medium to fast | ||
| Blood Meal | 12.5 | 1.5 | 0.6 | Medium | 6 to 8 weeks | |
| Bone Meal (raw) | 2 to 6 | 15 to 27 | 0 | Slow to Medium | 6 weeks | can burn plants |
| Bone Meal (steamed) | 0.7 to 7 | 18 to 24 | 0 | Slow to Medium | 2 to 4 months | |
| Castor Pomace | 5 | 1.8 | 1 | Slow | ||
| Clover, Crimson | 2 | 0.5 | 2 | Slow | 2 to 6 months | Cover crop |
| Cocoa Shell Meal | 2.5 | 1 | 2.5 | Slow | ||
| Compost | 1.5 to 3.5 | 0.5 to 1 | 1 to 2 | Slow | ||
| Cottonseed Meal (dry) | 4 to 6 | 2.5 to 3 | 1.6 | Slow to medium | 4 to 6 months | Acidic |
| Crab Meal | 10 | 0.25 | 0.05 | Slow | 4 to 6 months | |
| Crab Waste | 30 | 21 | 5.5 | |||
| Cucumber Skins (burned) | 0 | 11 | 27 | Fast | ||
| Eggshells (burned) | 0 | 0.5 | 0.3 | Fast | ||
| Feather Meal | 15 | 0 | 0 | Slow | 4 to 6 months | Best if ground up. |
| Fish Emulsion | 5 | 1 | 1 | Fast | 2 weeks | Spray foliage or apply dilute solution to soil. |
| Fish Meal (dry) | 10 | 4 to 6 | 0 | Medium | 4 to 6 months | |
| Fish Scrap (dry) | 3.5 to 12 | 1 to 12 | 1 to 1.5 | Slow | Bury deep; attracts 4-legged pests. | |
| Granite (dust) | 0 | 0 | 3 to 6 | Very slow | 3 to 5+ years | |
| Greensand | 0 | 1.5 | 5 | Very slow | 5+ years | Improves water retention |
| Hair | 12 | 26 | 0 | Very slow | 4 to 12 months | |
| Hoof/Horn Meal | 9 to 14 | 1.5 to 2 | 0 | |||
| Kaolinite (clay) | 0 | 0 | 12 | Medium | ||
| Kelp | 1 | 0.5 | 4 to 13 | Slow | 4 to 6 months | Contains potassium chloride, sodium carbonates, sodium, sulfates, potassium sulfates. |
| Cattle manure (fresh) | 0.5 to 1.5 | 0.2 to 0.7 | 0.5 to 2 | Medium | 2 years | |
| Cattle (dairy) manure (fresh) | 0.5 to 2 | 0.3 to 0.5 | 0.4 to 1.5 | Medium | 2 years | |
| Duck Manure (fresh) | 2.6 | 0.8 to 1.4 | 0 | |||
| Goat Manure (fresh) | 4 | 0.6 | 1 to 2.8 | Medium | Concentrated; compost first | |
| Goose Manure (fresh) | 3.3 | 0.4 | 0.6 | Medium | Concentrated; compost first | |
| Horse Manure (fresh) | 0.7 to 1.5 | 0.2 to 0.7 | 0.6 to 0.8 | Medium | 2 years | |
| Pig Manure (fresh) | 0.4 to 2 | 0.5 to 1 | 0.4 to 1.2 | |||
| Pigeon manure (fresh) | 6.3 to 6.5 | 2.5 | 2.5 | |||
| Poultry (75% water) manure (fresh) | 1.5 | 1 | 0.5 | |||
| Poultry (50% water) manure (fresh) | 1.5 to 2 | 1.8 to 2 1 | Medium to fast | |||
| Poultry (30% water) manure (fresh) | 3 to 4 | 2.5 | 1.5 | Medium to fast | 2 years | Best when composted |
| Poultry (15% water) manure (fresh) | 6 | 4 | 3 | Medium to fast | 2 years | |
| Rabbit manure (fresh) | 3 to 4.8 | 1.5 to 2.8 | 1 to 1.3 | Medium | ||
| Sheep manure (fresh) | 2.2 to 3.6 | 0.3 to 0.6 | 0.7 to 1.7 | Medium | ||
| Turkey manure (fresh) | 5 | 0.5 | 0.6 to 0.9 | Medium to fast | ||
| Marl | 0 | 2 | 4.5 | Very slow | ||
| Mushroom Compost | 0.5 to 0.8 | 40 to 55 | 0.5 to 0.8 | Slow | Often has high salt content. | |
| Peas, Austrian Winter | 2 to 3 | 0 | 1 | Slow | 2 to 6 months | Cover crop |
| Peat and Muck | 1.5 to 3 | 0.25 to 0.5 | 0.5 to 1 | Very slow | ||
| Phosphate, Colloidal | 0 | 17 to 25 | 0 | Slow | 3 years | |
| Phosphate, Rock | 0 | 17 to 30 | 0 | Very slow | 5+ years | |
| Rye, Annual | 1 | 0 | 1 | Slow | 2 to 6 months | Cover crop |
| Sawdust | 0.1 | 0.05 to 0.1 | 2 to 4 | Very slow | 2 to 4 years | Causes nitrogen deficiency |
| Seaweed | 0 to 2 | 0 | 0.5 to 1 | Fast | Foliar spray | |
| Shrimp Shells | 1.3 | 1.0 | 0 | |||
| Shrimp Waste | 25 | 20 | 1 | |||
| Sodium Nitrate | 16 | 0 | 0 | Fast | Restricted to no more than 20% of crops total N requirement. | |
| Soybean Meal (dry) | 6.5 | 1.5 | 2.4 | Slow to medium | ||
| Sulfate of potash magnesia | 0 | 0 | 22 | 22% sulfur, 11% magnesium | ||
| Urine soaked bedding | 36 to 42 | 0 | 0 | Fast | ||
| Wine Grape Compost | 1.5 | 2.0 | 0.5 | |||
| Wood Ashes | 0 | 5 | 3 to 7 | Fast | 1 to 4 months | Alkaline; contains 32% CaCO3. Fireplace ashes may contain toxic metals. |
| Wool Wastes | 5 to 6 | 2 to 4 | 1 to 3 | Very Slow | 4 to 9 months | May mat into layers. |
| Worm Castings | 1.5 | 2.5 | 1.3 |
