Why do we need fertilizer?
Plants require 16 nutrients for optimum growth. Often, the soil doesn't hold enough of these nutrients in the quantities needed for desirable growth and production. The nutrients, that are in the soil, are often used up and need to be replaced.
Nutrients, such as nitrogen, are easily leached by water and can also be volatilized into the atmosphere. These nutrients are usually not available, in sufficient quantities, from the soil. Therefore, we need to add extra plant nutrients to the soil ( or in some cases, on plant foliage ) to obtain maximum plant performance. We add these nutrients by applying fertilizer. For more information about the nutrients required by plants, see the article "Essential Plant Nutrients".
What is fertilizer?
Fertilizer is any material that supplies one or more of the essential nutrients to plants. Fertilizers can be classified into one of two categories: organic or inorganic. Organic fertilizers are derived from living or once living material. These materials include animal wastes, crop residues, compost and numerous other byproducts of living organisms. Inorganic fertilizers are derived from non-living sources and include most of our man-made, commercial fertilizers. For more information about both categories of fertilizers, see the articles "Organic Fertilizer Sources" and "Inorganic Fertilizer Sources".
What kind of fertilizer should I use?
Several considerations should be made before deciding on a fertilizer choice. First of all, you need to consider the nutritional needs of the crop for optimum performance. Secondly, you need to have you soil analyzed to see what is available in the soil. After you know what your crop needs and what is available in the soil, you can determine the nutrients and the amounts that you need to add to the soil.
The amount of each nutrient, that you need to add to the soil, will determine your choice of fertilizer. Choose the one that best matches your needs. You may find that you will need to use two or more types because one type may not satisfy all of you crops needs.
As for organic verses inorganic types, both have their advantages and disadvantages. Inorganic types are easier to use and we have more control over the content of nutrients in these sources. This allows us to apply our nutrients more accurately. Organic sources are variable in their nutrient content and we have very little control over this. However, organic sources can sometimes be obtained for little or no cost, it adds valuable organic matter to the soil and has some slow release action. Again, for more detailed information about each of these fertilizer sources, see the articles "Organic Fertilizer Sources" and "Inorganic Fertilizer Sources".
When should I apply my fertilizer?
Timing means everything to the efficient use of fertilizer. As a rule of thumb for all plants, fertilizer needs to be applied when the plant is actively growing. This timing will depend on the specific crop that you are growing. Before applying, know when your crop needs fertilizer and apply it so that the nutrients will be available when the plants need them.
Written by Kenny Bailey, Agricultural Extension Agent, NCSU