Soil pH

Target Soil pH

  • Target pH for most soils is 6.4 TIG
  • the majority of plants grow in the range 5.5-7.5: REOG
    • ornamentals tend to tolerate quite a wide pH range, although some (rhododendrons & heather) will grow only in more acid soils
    • vegetables prefer 6.5-7
    • fruit prefer 6-6.5
  • the range found in most soils is 4-8 REOG
  • Setting and maintaining the correct soil pH for your crops is one of the most overlooked factors for gardeners. Often tested and corrected in the beginning of the season, it changes as the season progresses.
    • even subsoil (down 2-3 feet) pH can limit root depth and therefore productivity
  • Calcium level of the soil controls pH; calcium can be washed out of the soil, making the soil more acidic REOG

pH Effects on Soil

  • Rate of chemical and biologic activity depends on pH (and other factors), which causes elements to be released from the solid phase into the soil solution, where they can be absorbed by plant roots
  • governs the availability of nutrients to plants REOG
  • has an effect on the diversity and activity of the soil life REOG
  • certain pests and diseases can be controlled by raising or lowering pH: REOG
    • potato scab: more troublesome in alkaline soils
    • clubroot: much less troublesome in alkaline soil
    • leatherjackets: more common in acidic soil
    • wireworms: more common in acidic soil
    • earthworms: (beneficial, not a pest) dislike acidic soil

Soil Nutrients Availability Determined by pH

Low soil pH (acidic)

  • increases uptake of:
  • decreases uptake of/reduces availability:
  • soil pH less than 6.4 isn’t necessarily a result of too little lime or of too little calcium, but a result of the soil’s CEC holding too many hydrogen ions and not enough of the essential cations TIG

High soil pH (basic/alkaline)

  • increases uptake of Molybdenum (Mo)
    • liming corrects Mo deficiency
  • decreases uptake of:
  • soil having water pH of 8.2 or higher are known as calcareous soils, due to free calcium carbonate (CaCO3) in soil PNSF
  • large quantities of calcium in the soil result in higher pH readings TIG
  • alkaline soil high in sodium (Na) are commonly deficient in calcium (Ca) PNSF
  • high pH can also indicate there is an excess of any of the 3 major cations (Ca, Mg, or K) TIG
  • liming to adjust pH without evaluating other characteristics of the soil will usually backfire TIG

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