Types of Fertilizers:
The word organic, applied to fertilizers, simply means that the nutrients contained in the product are derived solely from the remains or by-products of a once-living organism.
Urea is a synthetic organic fertilizer, an organic substance manufactured from inorganic materials. Cottonseed meal, blood meal, bone meal, hoof and horn meal, and all manures are examples of organic fertilizers.
When packaged as fertilizers, these products will have the fertilizer ratios stated on the labels. Some organic materials, particularly composted manures and sludges, are sold as soil conditioners and do not have a nutrient guarantee, although small amounts of nutrients are present. Most are high in one of the three major nutrients and low in the other two, although you may find some fortified with nitrogen, phosphorus, or potash for a higher analysis. Many are low in all three.
In general, organic fertilizers release nutrients over a fairly long period. The potential drawback is that they may not release enough of their principal nutrient quickly enough to give the plant what it needs for best growth. Because organic fertilizers depend on soil organisms to break them down to release nutrients, most of them are effective only when soil is moist and soil temperature is warm enough for the soil organisms to be active. In addition to providing nutrients, organic fertilizers increase organic content of the soil; improve the physical structure of the soil; and increase bacterial and fungal activity, particularly the mycorrhiza fungus, which makes other nutrients more available to plants.
In general, synthetic fertilizers act more quickly than organic types, though some organic materials release their nutrients quite rapidly. It isn't possible, therefore, to make a blanket statement about the long-term effects of fertilizers, except that organic materials such as manures and plant waste do usually help improve the soil structure while adding nutrients while chemical fertilizers do not affect soil structure. General-purpose synthetic fertilizers have the advantage of being readily available to the gardener and relatively inexpensive. If applied incorrectly, synthetic fertilizers "can be detrimental to earthworms" because most are in a salt formulation. Always follow label directions.
Complete vs. Incomplete Fertilizers
A fertilizer is said to be complete when it contains nitrogen, phosphorus, and potassium (10-10-10, 5-10-10, 5-30-5, etc.). An incomplete fertilizer contain one or two of the major components. Examples would include triple super phosphate (0-46-0) and potassium nitrate (13-0-44), ammonium nitrate (33.5-0-0). An incomplete fertilizer might be used in situations where the soil tests very high for phosphorus and potassium. In this example, a nitrogen-only fertilizer such as ammonium nitrate (33.5-0-0) would be an appropriate material to use. Application rates for this product are typically 1/2 lb. per 100 sq. ft.
Fertilizers come in many shapes and sizes. Different formulations are made to facilitate types of situations in which fertilizer is needed. Packaging for all formulations must show the amount of nutrients contained, or the analysis, and sometimes it tells how quickly a nutrient is available. Some of the formulations available to the homeowner are: granular solids, water-soluble powders, slow-release spikes, liquids, and tablets.
In most fertilizers, a "filler" is added to bulk up the fertilizer. This is done to lower the analysis, allowing a more even spreading pattern as compared to trying to spread a small amount of a high analysis over an area. A filler is generally an inert material such as sand, lime, ground corn cobs, etc. Some fillers are used to enhance the fertilizer's handling qualities.
Not all types of formulations are commonly used by homeowners for vegetable gardens. The most common and readily available formulations are:
This is the most common type of fertilizer applied to the garden. Examples are 10-10-10, 5-10-5, and 5-10-10. The manufacturer treats the material so that it has large more evenly sized grains. Granules spread more evenly and easily. Sometimes granules are coated to prevent moisture absorption.
Liquid fertilizers come in a variety of different formulations, including complete and incomplete. All are made to be diluted with water; some are concentrated liquids themselves, while others are powder or pellets. Fertilizer solutions are often used to water-in transplants, providing an immediately-available supply of nutrients for fast root growth and plant establishment. Liquid fertilizers may also be applied to plant foliage where the nutrients are absorbed directly through the leaf surface. This foliar feeding provides nutrients to the plant very quickly.
There are several choices of fertilizers for liquid application. Commercial soluble fertilizers, or transplant starter, are readily available and easy to use. Granular fertilizers are not satisfactory because the phosphorus is not soluble. Fish emulsion and liquid kelp (a seaweed) are good commercial organic sources. Follow label directions for each of these.
There are different methods of applying fertilizer depending on its formulation and the crop needs.
A recommended rate of fertilizer is spread over the growing area and incorporated into the soil with a roto-tiller or spade. Broadcasting is used over large garden areas or when time or labor is limited.