Understanding The Phosphorus Cycle
There are several factors that affect phosphorus within the phosphorus cycle – inputs to the soil, losses from the soil, and components in the soil. These elements are important for understanding nutrient and fertilizer management.
Phases of the phosphorus cycle
- Inputs to the soil
- Losses from the soil
- Components of the environment
- Plant uptake
Phosphorus inputs to the soil
Animal manure/biosolids
Animal manure is an important source of phosphorus – the quantity of phosphorus in the manure depends on the animal species, their age and diet, and bedding material. Once manure and biosolids are in the soil, they are considered organic phosphorus.
Plant residues
The crops that aren’t harvested leave behind residue better known as organic phosphorus. Phosphorus in plant residues becomes available as the residues are decomposed by soil organisms.
Atmospheric deposition
Atmospheric deposition is commonly known as dust settling onto the soil surface. This dust comes mostly from wind erosion.
Mineral fertilizers
Many times, depending on the need of the soil, producers will add phosphorus to their fertilizer profile. As the actual element reaches the soil and it goes through the oxidization process it is then converted into phosphate.
Phosphorus losses from the soil
Crop harvest
Since phosphorus is absorbed by the crops as phosphate, this is the amount of phosphorus that is removed from the field by harvesting the crop. Use the eKonomics nutrient removal calculator to find out much phosphorus, and other nutrients, you should be replacing.
Runoff/Erosion
Runoff is water that is not absorbed into the soil. Erosion is the wearing away of the soil through rain, irrigation, wind and ice. Because much of soil phosphorus is associated with the solid materials in soil, these actions result in phosphorus loss from the soil. Runoff and erosion can be minimized by maintaining soil cover with crop residue and/or cover crops.
Leaching
Leaching is the removal of dissolved phosphorus from soil by vertical water movement.
Phosphorus components of the environment
Organic phosphorus
Organic phosphorus becomes available when soil organic matter, like animal manure, biosolids and plant residues, is decomposed by soil organisms.
Soluble phosphorus
Soluble phosphorus is the portion of soil phosphorus immediately available to plants. As plants take up soluble phosphorus, it is replenished by phosphorus from organic and mineral sources and fertilizers. Rate of this replenishment determines soil ability to meet plant needs.
Primary minerals
The primary mineral within the soil contributing to the phosphorus cycle is a group of phosphate minerals, usual pale green to purple in color. Calcium phosphates are common in soils of slightly acid to alkaline pH. Iron and aluminum phosphates dominate in very acid soils.
Mineral surfaces
Minerals found within the soil can affect phosphorus chemistry. Minerals within the soil can be clays, silicates, carbonates and iron and aluminum oxides and hydroxides.
Secondary compounds
Secondary compounds include calcium monophosphate, iron phosphide, manganese peroxidase and aluminium phosphide. These compounds help enhance the natural movement of phosphorus through the soil.
Plant uptake
In the soil, phosphorus is in two soluble forms, H2PO4- and HPO42-. The plant’s roots absorb the phosphorus as phosphate from the soil.
Phosphorus plays a vital role in plant development. Each factor throughout the phosphorus cycle should be considered when evaluating nutrient management practices to maximize plant nutrient uptake to realize crop yield potential.
Learn more about the phosphorus cycle over on eKonomics.
Learn more about Smart Nutrition MAP+MST as a phosphorus source here.
