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Soil pH affected by soil texture?

  1. Nov 28, 2006 #1
    How is soil pH affected by soil texture?
    any sites would be helpful alot.
  2. jcsd
  3. Nov 30, 2006 #2
    Soil PH is not affected by soil texture.

  4. Dec 12, 2006 #3

    jim mcnamara

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    Staff: Mentor

    From a soil science point of view - pH is determined primarily by the the ions extracted from the mineral surface of the soil particles and dissolved in soil water. So minerals like (Calcium carbonate) affect pH by driving it up. The presence of carbonic acid (CO2 + H2O ) or elemental sulfur drives it down, for example.

    Secondly, the longterm pH of rainfall (specifically from the acid rain effect) alters the pH of soils and groundwater. In this case it lowers pH.

    By texture I imagine you mean whether it's sandy, silty, loamy, or clayey, etc. -- soil texture classes. If that has an effect it would be small - it would be in the case where the exposed surface area of the soil particles varies that it affects pH by the release of mineral ions. Cation Exchange Capacity (CEC) has something to do with the amount of exposed surface area, and it is affected by soil's texture.

    I take your question to mean pH versus soil texture class for soils formed from the same substrate in the same climate. Don't know of any papers on the subject.

    The only thing I do know is that fine textured soils, like clays, require far more pH changing additives per acre (sulfur to lower pH, for example) to achieve a given pH change than do sandy soils.

    I guess we can infer that as texture becomes finer, resistance to pH changes increases. So that is an effect, but I don't think it's what you were after.

    And I also know that for a given substrate, as particles weather down to smaller size, the mineral content of the soil changes peferentially - some minerals tend to stay behind or accumulate - say montmorillonite, and others tend to "go away" lost to leaching.

    So if montmorillonite has a tendency to increase pH and the "washed away" components did the opposite, then the clay soil texture class of a substrate would have a higher pH than the sandy one. But this is an effect of weathering more than of soil texture class. IMO, anyway.

    Actually - a good question.
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