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Water & Soil

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Not free from errors, as student contributions

Not free from errors, as student contributions

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  • 1. Water & Soil Assessment Statements E.12.2 State what is meant by the term cation-exchange capacity (CEC) and outline its importance E.12.3 Discuss the effects of soil pH on cation-exchange capacity and availability of nutrients
  • 2. E.12.2
    • Cation-exchange capacity (CEC) is the capacity of a soil for ion exchange of cations between the soil and the soil solution.
      • Cation is a positively charged ion
    • CEC is used as a measure of fertility, nutrient retention capacity, and the capacity to protect groundwater from cation contamination
    • The two main particles in the soil are clay and humus
  • 3.
    • The CEC of the soil is determined by the amount of clay and/or humus that is present.
      • Cation ‘warehouse’
      • Nutrient and water holding capacity
    • Sandy soils with very little organic matter have a low CEC
    • Heavy clay soils with high levels of organic matter have a much greater capacity to hold cations.
  • 4. E.12.3
    • Rise in pH = rise in CEC 
    • Acidic soil will have high concentrations of H+ and Al3+
    • In neutral to moderately alkaline soils, Ca2+ and Mg2+ will be prevalent
    • Exchangeable cations are available to plants
    • pH can have the following effects:
      • K uptake by plants is limited by high levels of Ca in some soils. 
      • High levels of K can in turn, limit Mg uptake even if Mg levels in soil are high.