Sources of Phosphorus


  Historical Information
  Phosphorus Functions in Plants
  Nature and Transformations of Soil Phosphorus
Diagnosing Phosphorus Deficiency
  Visual Symptoms of Deficiency and Excess
  Tissue Testing for Phosphorus
  Soil Testing for Phosphorus
Factors Affecting Management of Phosphorus Fertilization
  Crop Response to Phosphorus
  Soil Water
  Soil Temperature
  Sources of Phosphorus
  Timing of Application of Phosphorus Fertilizers
  Placement of Phosphorus Fertilizers
  Foliar-Applied Phosphorus Fertilization
  Fertilization in Irrigation Water

Most phosphorus-containing fertilizers are derived from mined phosphate rock. In some unique production situations on acidic soils, phosphate rock can be used directly as a phosphorus source. Most cropping systems show the best response to water-soluble phosphorus fertilizers. Water-soluble phosphorus fertilizers are produced by reacting phosphate rock with sulfuric or phosphoric acid (90). Ammonium phosphates are made by passing anhydrous ammonia through phosphoric acid. This production includes diammonium phosphate and monoammonium phosphate.

The agronomic effectiveness of phosphorus fertilizers was reviewed by Engelstad and Terman (91). Most crops require readily available phosphorus, and most soluble sources perform similarly. However, in some situations the ammonium phosphates produce phytotoxicity (92), and their use is often discouraged when high amounts of phosphorus are required. For example, for economic reasons, diammonium phosphate typically is broadcast applied for lettuce production in the southwestern desert, but its use is discouraged when broadcast rates are high or when phosphorus fertilizer is banded near the plants.

Soluble, dry fertilizers and solution fertilizers perform similarly under many production systems. However, there are some unique production situations where solution sources may present logistical advantages. Often solution sources are easier to use in band placement or point-injection technologies. Generally, solution sources would be utilized in application with irrigation water.

In conclusion, under most conditions, cost considerations, available application technologies, and the potential for phytotoxicity are the major determining factors influencing the selection of sources of phosphorus fertilizers.