Fertilizers are used in the garden to promote growth and prevent disease. Organic and chemical fertilizers are available, both with their individual qualities and physical properties. Knowing the makeup of fertilizers gives you a greater control over how fertile your soil is, how to apply the fertilizer, and which fertilizer will work best in your garden.
The main body of fertilizer contains the nutrients that adhere to the soil when applied. Chemical fertilizers will generally carry only the three main macronutrients, according to the University of Minnesota Extension--nitrogen (N), phosphorous (P) and potassium (K). These are the main three nutrients needed by all plants to grow properly. The nutrient analysis is printed on the side of the fertilizer bag or box using three numbers representing N, P and K in that order. A 10-10-10 is 10 percent of each nutrient by weight. A 100-lb. bag of fertilizer will contain 10 lbs. of each nutrient.
Granules and liquids
Chemical fertilizers are sold in two physical forms; water-soluble granules and dry granules. Water-soluble fertilizer granules are dissolved in water and sprayed over the lawn or garden using a pressurized sprayer. Dry granules are pellets with a light covering that are spread over the lawn using a drop or broadcast spreader. Activation of the fertilizer requires a spray of water.
Organic fertilizers are made out of plant material or animal manure. These materials are built out of a complex array of organic matter, according to Utah State University Cooperative Extension. The organic matter absorbed water and decays slowly, adding microorganisms to the soil which breaks down other organic material, adding nutrients to the soil. The physical properties of organic material break down into a soil called "humus," which is rich in nutrients and spongy in texture.