What Is the Origin of Phosphorus in Soil?

The Phosphorus Cycle

• The phosphorus cycle is the natural cycle by which phosphorus is transferred through the different levels of the ecosystem and then is returned to the soil. The phosphorus in the soil is absorbed by plants, which can then die and decay. In this decay process, the dead plant matter is broken down into its nutrients, which are then returned to the soil -- including phosphorus. Alternately, the plants can get consumed by animals, which will also get returned to the soil when their bodies are acted upon by microorganisms and bacteria. Once this material has decayed, it must be further broken down in order to be returned to a state which can be used by plants again.

Organic Fertilizers

• When there is not enough phosphorus in the soil to support the plant life that is growing there, organic fertilizers can be added to increase the phosphorus content in the soil. This includes different kinds of manures from that collected from livestock such as dairy cows to chickens. Each type of manure has a different amount of phosphorus in it, but this application will quickly return the nutrient to the soil as it is contained in the animal's feed and passed through their system. Since organic fertilizers usually contain other nutrients like nitrogen, they are usually applied when the soil is lacking in more nutrients than just phosphorus. Humus and peat are other types of organic fertilizers that contain phosphorus.

Inorganic Fertilizers

• Inorganic fertilizers are those which are created commercially and manufactured to contain a certain percentage of each of their nutrients. Soil tests can determine what is lacking, and an inorganic fertilizer can be chosen that will effectively replace all the needed nutrients. Because the compound of phosphorus that is created in these commercial fertilizers can easily react with other nutrients in the soil, lime is sometimes applied first to adjust soil pH and neutralize these reactions. In order to be used efficiently, this phosphorus must be absorbed into the plant quickly before reactions that tie up the molecules in other compounds occur.

Runoff and Phosphorus Transfer

• When too much phosphorus is added to the soil, it can easily leach into groundwater and be transferred to other areas. When the plants that are in the soil cannot sufficiently absorb all the phosphorus that is available to them, soon after fertilizers are applied, runoff can quickly carry the fertilizers away and into nearby bodies of water. Here, the phosphorus can cause algal blooms and other detrimental effects within the water. When fertilizers are necessary for the return of phosphorus to the soil, it is vitally important that the soil does not become over-saturated, as this can be as detrimental to the environment as a lack of the nutrient.