The main factor affecting plant growth is the fertility of the soil being used. When soil is not properly managed during agricultural processes, soil fertility is lost. The use of fertilizers improves soil fertility, providing the essential nutrients that plants need to grow when the soil does not provide for basic needs.
Plants require 16 nutrient elements to properly grow. Fertile soil will include all of these elements. As plants grow and leach nutrient materials from the soil, the soil loses its ability to grow plants properly. The major three elements required by plants are nitrogen (N), phosphorous (P) and potassium (K). These are needed in larger amounts, and are called macronutrients. The other 13 nutrients are required in smaller amounts and are called micronutrients.
Soil testing, says the Utah State University Cooperative Extension, is the ideal way to determine a fertilization schedule. Tests for pH determine the relative acidity of the soil. Performing a pH test indicates the correct amount of fertilization that is required to balance the acidity of the soil. These pH tests are available from local gardening centers or soil tests can be sent to a local university extension for a lab test. Lab tests from university extension programs usually include recommendations for fertilizer application.
The limiting factor is the nutrient, or nutrients, in the soil that are deficient. The limiting factor affects the plant yield. Determining the limiting factor helps specify which nutrients need to be added to the soil to increase plant production. Adding large amounts of nitrogen to a soil deficient in phosphorous does not improve plant yield.
Fertilizers are broken up into two main groups; organic and inorganic. Organic fertilizers come from plant or animal sources such as decaying crops, animal manure or compost. Chemical fertilizers are manufactured to provide nutrients to the soil, and are often cheaper than organic fertilizers. Organic fertilizers provide a slow release of nutrients, while chemical fertilizers provide a quick release, providing the nutrients immediately. Chemical fertilizers, however, do not provide organic material to the soil, which improves its structure and nutrient retention, while organic fertilizer does.
Depending on the plant crop and the fertilizer variety, fertilizers are applied at different times of the year. When applied on hills or in erosive areas, fertilizers are placed 1 or 2 inches below the depth of the plant seed. The soil is best fertilized before the planting of seed or a transplant, then "side-dressed" with another application of fertilizer during the fruiting or production period. Grasses require fertilization depending on their nutrient needs, with high-maintenance turfgrass requiring more than low-maintenance grasses. Chemical fertilizers are often combined with pesticides to reduce pests in the crop.