Soluble P may percolate through the soil, be used by plants or microorganisms, enter the reactive pool, be transformed into secondary minerals, or be lost in runoff. Total P is all the P that exists in soils. Solution P is a very small amount, can be drawn out with water or a dilute salt, and is mostly the plant available orthophosphate form. Reactive P is the fraction most soil tests extract. Occluded and P in primary minerals is relatively insoluble and resistant to weathering.
Organic P is found in organic matter.
This process is called mineralization and is most rapid in warm, moist, and well-drained soils. Assuming a plow layer weight of 2,000,000 pounds per acre, total P is 100,000 pounds. The average soil loss due to water erosion for cropland in Iowa is 5 tons per acre. If soil loss is 15 tons per acre, P loss is 1,500 pounds per acre. Reducing P loss by controlling erosion is an important part of P management.