This is good link that describe each type of organic fertilizer
http://www.rdrop.com/~paul/organics.html
A PRIMER ON SOIL - ORGANIC AMENDMENTS
By Richard Hedenberg, ARS Consulting Rosarian
Organic amendments are any materials that have ever been alive either as plant or animal. Nutrients from organics are not immediately available to the plant. Soil microorganisms are needed to change nutrients through bacterial action into forms the plants can use in solution. Organics give a steady supply of nutrients over a long period of time, however, some, such as fish based products, become available quite quickly in warm moist soil. Organics are primarily a source of nitrogen and trace elements, but many also provide some phosphates and potash. Organics in quantities up to one third of the total soil volume are very beneficial to the soil structure. The organics are converted by the microorganisms and are used by the plant. Therefore, they should be replaced at the rate they are used.
ALFALFA MEAL (3N-lP-2K)
Alfalfa meal or pellets is one of the green manure crops and contains small amounts of nitrogen, phosphorous and potassium which feed the plant. However, the biggest benefit of alfalfa is from the work it does in the soil. Alfalfa contains the hormone, Triacontanol, a plant growth regulator. Alfalfa meal can be top dressed and watered in. But quicker benefits are had when alfalfa is brewed into a tea. The primary boost comes from the millions of microbes in the fermented meal that activate the soil organisms that then convert nutrients into forms available to plants. Roses love it. Only apply alfalfa to the surface. If placed in the root zone, the rapid decomposition of alfalfa will generate heat which can damage the roots.
BLOOD MEAL (12-2-1)
Blood meal is a slaughter house by-product and is an excellent source of quickly available organic nitrogen, when used as a top dressing and watered in. Blood meal is completely soluble and can be mixed with water and used as a liquid fertilizer. Meal fertilizers, when not brewed, work best when they are scattered on top of the bed and watered in. Meals blended in the soil can become hot (called curing). All meals are used up fast. Bacterial action works quickly.
BONE MEAL (2-12-2)
Bone is used as a long-lasting source of phosphorous as well as low levels of nitrogen, potassium and calcium. The extremely slow availability of nutrients from bone meal make it a very safe fertilizer, especially when planting of potting very young or new plants.
COMPOST
Compost is the decomposed, cured form of organic matter. Compost, worked into new beds or top dressed and watered into established beds, increases microorganism activity and improves soil character and moisture retention. There is some nutrient value as well. The best source for good compost is making your own.
COTTONSEED MEAL (7 2-2)
Cottonseed meal is a good natural fertilizer with a high percentage of organic nitrogen, perhaps the second best source of organic nitrogen after blood meal. Cottonseed meal is easily obtained at your local feed store. The nitrogen is broken down slowly and is available to the plant over a period of time. Cottonseed meal acidifies the soil.
EARTHWORMS
Worms are nature's own tillers and soil conditioners. Their main benefit is to soil structure where their many tunnels loosen the soil, improving aeration and drainage. Worms don't make the soil healthier, but are an excellent indication of healthy soil. If your pH is way off, earthworms won't stay around. They will leave if they don't like it. Earthworms can be introduced to new beds, but will eventually find their own way to them.
FISH EMULSION (8-12-2)
Fish emulsion is an all-natural organic fish fertilizer with a reputation for eliminating plant doldrums. Many exhibitors refer to it as their secret to growing show winning blooms. When used as a liquid drench, results are quicker than with other organics. It is a low-nitrogen concentrated liquid food containing a wide range of trace elements that will green foliage, grow vigorous roots and big blooms while also enriching the soil. A must for Miniatures. The odor dissipates rapidly.
FISH MEAL (8-12-2)
Fish meal is a great natural fertilizer, high in phosphorous and high in organic nitrogen. Fish meal is quick acting, offering a sustained supply of nutrients. Don't scatter fish meal, because of the strong odor; plug it in a series of holes about ten inches deep that can then be covered with about four inches of soil.
GROUND TREE BARK
Ground bark is sold as a soil conditioner which improves drainage. It has good water holding capacity and eventually breaks down to humus. Tree bark reportedly has a deterrent effect against nematodes. Many rosarians like to use it in an chunk form for mulch. It's use will cause a temporary drop in nitrogen levels in the soil so additional amounts of nitrogen must be added.
MANURES
Manures are a good source of nutrients and organic matter. Aged horse manure can be found in this area and is the preferred one of the manures, excellent as a soil conditioner for any kind of soil or as a mulch. In addition to being an organic source of nitrogen, decomposing manures are chelating agents that function to make trace metals available to plants. Dehydrated cow manure (2-1-2), dried and pulverized comes in fifty pound bags. It has been heat treated to kill weed seeds and is convenient, easy to apply and long-lasting. Manures may be high in salts. About half of the nutrients remaining in manures will be available each year.
MILORGA NITE (6-2-0)
Milorganite is 100% natural organic heat dried activated sewage sludge in a fine granular form. Heat treated for sterilization, it is inoffensive and easy to handle. A high nitrogen source that is also a good source for iron and trace elements that are slow release. Milorganite is easy to top dress with and water into beds and also won't burn roots when used in a soil mix.
SEAWEED PRODUCTS
Kelp meal (1-0-8) is a dry fertilizer made iron seaweed and is very high in potassiumand trace elements. An excellent source of plant hormones that stimulate plant and root growth. Liquid seaweed (4-2-3) has the same characteristics as kelp meal and is a quick boost for greening foliage. When mixed with fish emulsion, it can't be beat.
SPHAGNUM PEAT MOSS
Peat moss is an excellent, long lasting, slow decaying organic material whose greatest value is as a soil amendment promoting moisture retention and improving soil structure. Peat moss can hold water and nutrients ten to fifteen times its own weight when fully saturated and can still hold 40% air. It has little nutrient value itself but is excellent at holding nutrients to prevent them from leaching iron the soil. It will then release them to the plant. Do not apply to the surface. Sphagnum peat moss will repel water when dry. However, once wet and mixed with the soil, it will readily take up moisture. It increases soil acidity, so lime should be added to the sphagnum peat moss at the time of application. Its good traits last about five years before it is decomposed, which explains the logic of not planting a new rose in an old rose hole.
This article originally appeared on ARS's home page. Credit: the ARS and Richard Hedenberg.
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