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SOIL CHEMISTRY
cation exchange capacity (CEC) - milliequivalents per 100 grams dry soil; meq/100 g
Component
CEC (meq/100 g)
sand
2-4
silt
4-10
clay
10-100
organic matter
150-300

percent base saturation - % of total CEC occupied by basic nutrients, such as Ca+2, Mg+2, K+,
                                         and/or Na+ (as opposed to acidic H+ and Al+3
 

pH- negative log of the hydrogen ion concentration;    pH  =  -log [H+]  =  log 1/[H+]

    pH is a measure of the acidity of a solution.  Below pH 7 is acid, pH 7 is neutral, and above pH 7 is basic.  pH is seldom high or low enough to directly effect plants. Its major effect is on the solubility of nutrients in the soil solution, i.e. nutrient availability. 
     
    Nutrients That Are More Available at 
    Low pH (below pH 5.5)
    Intermediate pH (pH 6-7) 
    High pH (above pH 6.5 )
     Fe, Zn, Cu, Mn, B 
     P 
    N, K, Mg, Ca, S, Mo 
    How to Increase or Decrease Soil or Growing Medium pH
    Chemicals that Increase pH Chemicals that Decrease pH
    • calcitic lime - CaCO3
    • dolomite - CaCO3 /MgCO3
    • hydrated lime - Ca(OH)2
    • burned lime - CaO 
    • basic fertilizers (nitrate)
    • elemental sulfur -S  
    • aluminum sulfate - Al2(S04)3
    • iron sulfate - FeSO4  
    • acidic fertilizers (urea, ammonia, ammonium)
TYPE SOILS BASED ON CHEMICAL PROPERTIES
A) Acid Soils - soils with acid pH; in regions of high rainfall

B) Basic or Alkaline Soils - soils with basic pH; in arid regions
    3 Types:
    1) saline soil - pH 7-8.5, and has greater than 2,000 ppm total soluble salts.
    2) sodic soil- pH 8.5-10, low to moderate total salts, but 15% or more of CEC is occupied by Na.
    3) saline-sodic soil- pH 8-8.5, greater than 2,000 ppm total soluble salts and 15% or more of 
                                    CEC occupied by Na.

    How to improve saline, sodic or saline-sodic soils
    a) leach - application of large volumes of water to remove excess soluble salts.
    b) add elemental sulfur (S) - acidifies the soil
    c) add gypsum (CaSO4) - Ca promotes good soil structure, drainage and Na leaching