Fertilizer is classified as organic or inorganic. Organic fertilizer is derived form natural sources such as alfalfa meal, feather meal, bat guano, seaweed, blood meal, cottonseed meal and fish meal. Compost is also organic fertilizer. Inorganic fertilizer is made from chemical compounds such as nitrogen, phosphorus and potassium, which are the macro-nutrients plants need in the highest amounts. Micro-nutrients, or trace elements, are also needed to produce healthy plants.
Soil is 45 percent minerals, 25 percent each oxygen and water, and 2 to 5 percent organic matter, according to the National Sustainable Agriculture Information Service. It contains a population of living organisms that feed, reproduce and create nutrition for vegetables, fruits, and landscape plants. Inorganic fertilizer feeds nitrogen, phosphorus and potassium directly to plant root systems to produce green growth, blooms and vegetables.
Inorganic fertilizer boosts plant growth quickly because it is water soluble and is delivered immediately through the root system to the growing plant. “Since they do not require microbial action to make them available to plants, these products are quick acting even in cool soils and they are inexpensive,” said Kenneth Schoessow of the University of Wisconsin’s Agriculture and Natural Resource Extension Service.
Plants live in a soil food web of billions of tiny living organisms that each has a role in creating nutrients for plants. Nitrogen-based inorganic fertilizer unbalances the life cycle of nutrient production by killing friendly bacteria and fungi. Bacteria, fungi, earthworms, insects and small mammals in the soil eat decaying organic matter and produce nutrients in their bodies. Nutrients are absorbed by roots into vegetables and fruit.
Soil Food Web
Soil needs to be fed organic matter to maintain life. According to the U.S. Department of Agriculture's Natural Resources Conservation Service, the soil food web includes a diversity of organisms ranging in size from the tiny one-celled bacteria, algae, fungi and protozoa, to more complex nematodes and micro-arthropods, to the visible earthworms, insects, small vertebrates and plants.
Feed the Soil
Soil is naturally depleted of nutrients as plants grow. Soil needs to be fed materials to make it fertile and continue its ability to support plant life. Organic fertilizer such as compost adds billions of microorganisms to the soil to feed plants. Inorganic fertilizer cannot provide materials to increase the growth of soil organisms; it can only directly boost plant growth.