• One of the 13 essential elements for plant growth and is one of the 6 Major Elements, based on concentration required
• principle form of uptake: ionic forms dihydrogen phosphate (H₂PO₄^–), monohydrogen phosphate (HPO₄^2-), and orthophosphate (PO₄^3-)
• amount required for healthy plant growth: 2,000 ppm, 0.2%, dry soil matter
• Soil conditions related to a deficiency of phosphorous:
  • mineral soils low in organic matter
  • long history of cropping without adequate levels of P
  • erosion of phosphorous-rich soils
  • calcerous soils: alkaline conditions reduce P availability (calcerous soils are mostly/partly composed of calcium carbonate (CaCO₃); soil having a water pH of 8.2 or more, due to fee calcium carbonate in soil; also, containing lime or being chalky)
• Soils frequently fertilized with phosphorous tend to be deficient in zinc (Zn)
• Phosphorous primarily moves through soil by diffusion
• Available phosphate is positively correlated to brix (high phosphate = higher brix)
• soil factors that affect uptake of phosphorous in the plant:
  • temperature
  • the level of decomposition of organic matter
  • soil test levels
  • low pH (acidic) soil decreases phosphorous uptake by plants
• plant factors that affect phosphorous uptake by plant:
  • hybrid or variety of plant
  • stage of growth
  • interactions with zinc (Zn) or manganese (Mn) and other elements

Roles of phosphorous in the plant:

• involved in energy transfer reactions as part of ATP (adenosine triphosphate)
• involved in genetic information processes as part of RNA and DNA
• is also a component of various enzymes and proteins, and phytin

Sources for Phosphorous:

• organic debris, plant residues, and microorganisms are the major sources of phosphorous

Phosphorous Deficiency Symptoms:

• purplish color on the lower leaves
• overall stunted growth
• Phosphorous is very mobile within the plant, so deficiency symptoms will first show in the older leaves, since the plant is moving P from older leaves to newer growth to supply growing points
• Phosphorous content in leaves naturally declines with maturity of the plant, so some symptoms of deficiency are normal in those older leaves, as the plant ages

Phosphorous Excess Symptoms:

• excess phosphorous can interfere with the metabolism and uptake of zinc