Calcium (Ca)

  • One of the 13 essential elements for plant growth and is one of the 6 Major Elements, based on concentration required
  • calcium is needed in much greater quantity than all the other elements combinedIG
  • calcium is naturally abundantIG
  • principle form of uptake: ionic form (Ca2+)
  • amount required for healthy plant growth: 5,000 ppm, 0.5%, dry soil matter
  • soils with too much free calcium carbonate (CaCO3) are known as calcareous, and have very high pH (8.2+)
  • calcium & magnesium determine the soil’s mechanical properties
    • the amount of calcium versus magnesium on the exchange points determines if the soil is open & airy or loose or tight & airless (too much Mg means tight & airless soil)
    • this ratio also determines if the clay portions cling to themselves or open and separate
    • If Ca is in excess, and Mg is deficient, soil is extremely loose; water flows through without sticking; getting Mg levels to target will improve this
    • also, this ratio has much more effect on the soil’s air supply than does organic matter
    • when calcium:magnesium ratio is correct, less compost is needed
      • ideal ratio for non-calcareous soil: Ca:Mg = 68:12
      • for calcareous soil: Ca:Mg = 85:5
  • calcareous soils are often deficient in phosphorous
  • soils over-fertilized with calcium and/or potassium are often deficient in magnesium (Mg)
  • Calcium is available to plant roots in its ionic form: Ca2+
  • calcium is the strongest of the cations, which means that it can knock other cations off of the exchange points in the soil (see Cationic Exchange Capacity for more info)
  • Ca2+ primarily moves through soil via mass flow, but also via diffusion
  • Brix test, using a refractometer, will show a fuzzy line of demarcation when calcium levels are sufficient (per Phil Nauta)
  • soil factors that affect calcium uptake by plants:
    • available levels in soil
    • decomposition of organic matter
  • plant factors that affect calcium uptake by plant:

Deficiency Symptoms:

  • thick, woody stems
  • cell death at the base of the leaves
  • soil conditions related to calcium deficiencies:
    • acidic, sandy soil subjected to high rainfall or irrigation
    • strongly acidic peats
    • alkaline soils with high sodium (Na)
    • soils with high soluble aluminum and low exchangeable calcium

Roles of Calcium in Plant Functions:

  • involved in the osmotic potential, balancing anions, controlling membrane permeability & electropotential
  • important for maintaining cell integrity and membrane permeability
  • enhances pollen germination and growth
  • activates enzymes for cell growth and division
  • may be important for protein synthesis and carbohydrate transfer
  • it may also help to detoxify the plant from heavy metals (chelation?)


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