Phosphorous (P)

  • 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 (HPO42-), and orthophosphate (PO43-)
  • 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

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