The U.S. Department of Agriculture's Organic Program established the certification program for organic fertilizers in 1990. The "USDA 100% Organic" label ensures the quality and non-synthetic content of organic fertilizer. It is made from naturally occurring materials, living organisms that enrich the soil and provide nutrients to growing plants. Organic fertilizers increase the water, nutrient-holding capacity and aeration in soil. Organic fertilizer adds microorganisms to soil which in turn feed earthworms, fungi and beneficial bacteria. There are several components found in organic fertilizers.
Bone Meal and Bat Guano
Bone meal is a slow-release substance that is high in phosphorus and calcium.It has essential micronutrients such as nitrogen, phosphorus and potassium. These elements are released from organic fertilizer when the soil is moist and warm, which coincides with the time of optimum need by growing plants. The slow-release capacity differentiates organic from non-organic fertilizers. Problems of chemical runoff into local water supplies is reduced through the use of slow-release organic fertilizers.
Poultry Humus and Fish Emulsion
Poultry humus is a combination of waste products from the chicken industry. It contains all three micronutrients necessary for healthy plant growth. Fish emulsion is high in nitrogen, phosphorus and trace elements. Fish emulsion was used as an organic plant food by itself before the commercial production of organic fertilizers. It is available at garden centers. Organic fertilizers also sometimes contain rock powders such as limestone, rock phosphate and Chilean saltpeter.
Fish Meal, Cotton Seed Meal and Seaweed
Similar to fish emulsion, fish meal is high nitrogen and phosphorus. Cotton seed meal is a waste product from the cotton industry that is very high in nitrogen. Nitrogen boosts green plant growth prior to fruit or blossom production. Seaweed (kelp) has a wide range of micronutrients that help produce healthy soil microorganisms. Healthy soil produces healthy plants. The University of Maryland Extension research on organic and non-organic fertilizers describes plants produced with organic fertilizer as "quite competitive" with plants produced by synthetic means.