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Liming Materials

Liming Materials. Ch 9.8. Agricultural Limes. Carbonate Forms Calcite (CaCO 3 ) Dolomite (CaMgCO 3 ) Marl Oyster shells Lime – Calcium oxide (CaO), also called quicklime or burned lime Hydrated lime – Ca(OH) 2 formed by mixing CaO with hot water. limestones. Reactions in the Soil.

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Liming Materials

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  1. Liming Materials Ch 9.8

  2. Agricultural Limes • Carbonate Forms • Calcite (CaCO3) • Dolomite (CaMgCO3) • Marl • Oyster shells • Lime – Calcium oxide (CaO), also called quicklime or burned lime • Hydrated lime – Ca(OH)2 formed by mixing CaO with hot water limestones

  3. Reactions in the Soil 1) Reaction with Carbon Dioxide CaCO3 + H2O + CO2→ Ca(HCO3)2 2) Reaction with Soil Colloids Colloid(H+,Al3+) + 2Ca(HCO3) → Colloid(2Ca2+)+Al(OH)3 + H2O+4CO2 Overall Reaction Colloid(H+,Al3+) + 2CaCO3+ H2O→ Colloid(2Ca2+)+ Al(OH)3 +2CO2 Results in an increase in base saturation, and a corresponding increase in pH

  4. How much lime is needed to raise pH? • Determined by: • Change in pH required • Buffer capacity of the soil • Chemical composition of the liming material • The particle size (fineness) of the liming material

  5. Effect of Soil pH and Soil Texture Lbs CaCO3 needed to raise pH to 6.5 Lbs/1000 ft2lime to apply Soil pH

  6. Chemical composition • Commonly expressed as CaCO3 equivalent (CCE) • chemical purity of material • Chemical equivalency • Moles of + or – charge per mole of ion or compound • Standard is CaCO3 = 2 equivalents/mole • Ca+2= Mg+2 = CaO =Ca(OH)2=MgO=CaCO3=MgCO3 • CaMg(CO3)2= 2 Ca2+ (4 equivalents/mole)

  7. 4 equivalents/mole Calculating Chemical Equivalency • Example: CaO (2 equivalents/mole) • CaO=56 g/mole, equivalent weight = 28 g/mole • CaCO3=100 g/mole, equivalent weight = 50 g/eq CCE= (50/28) x 100 = 178.6% 100 lb CaO will neutralize as much acidity as 178.6 lbs CaCO3!!! Try with dolomite CaMg(CO3)2 (M.W.=184.4) CCE = [50 /(184.4/4)] x 100 = 109

  8. Particle Size (Fineness) of Liming Materials • The finer the material, the faster it dissolves and reacts with soil • Oxides and hydroxides usually occur as powders • Limestones can vary in their particle sizes • Agricultural limes are required by law to have a “fineness guarantee” indicating its particle size and reactivity • Fineness is described in terms of sieves used for analysis

  9. 8 openings /inch 20 openings /inch 60 openings /inch

  10. Effect of Particle Size on Soil pH over 3 years Figure 3-10 from Havlin et al., 2005

  11. Sieves Used By State • Iowa – 4, 8, 60 mesh • Illinois – 8, 30, 60 mesh • Minnesota and Wisconsin – 8, 20, 60 mesh • Michigan – 8, 60 mesh

  12. Relative lime efficiency and rate with particle size To raise soil pH to 7.0 Figure 3-11 from Havlin et al., 2005

  13. Calculating fineness factor Sieve analysis multiplication factor > 8 mesh 0 8 – 20 mesh 0.2 20-60 mesh 0.6 < 60 mesh 1.0

  14. Example Calculation – fineness factor 100 g 16 g x 0 = 0 8 20 22 g x 0.2 = 4.4 60 35 g x 0.6 = 21.0 pan 27 x 1.0 = 27.0 Fineness Factor = 4.4 + 21.0 + 27.0 = 52.4

  15. The Wisconsin Neutralizing Index (NI) • Combines chemical composition (CCE) and fineness into one factor • Provides a relative value of various liming materials • NI = CCE x FF • Example: material with CCE = 92% and FF = 56 • NI = 56 x 0.92 = 51.5 • Wisconsin Lime Requirement based on lime with a NI = 60-69 and 80-89

  16. Other Liming Materials • Fly ash • Variable with type – metal contamination may be a problem, mainly oxides • Papermill/Waste treatment Sludge • Cheap, effective if source is near, mainly carbonates • Slag • Mainly, silicates, and oxides • Fluid lime • Finely ground limestone in suspension

  17. Management and Effectiveness • Limestone has effects up to 4 years after application • Incorporation into soil speeds the reaction • Topdressing aglime in no-till can be effective, but can take longer for effects to be seen • Soil texture, macropores are factors • Fluid lime can be effective in no-till but must weigh cost

  18. Effectiveness of Aglime in no-till and conventional tillage systems on clay soil Stevens and Dunn(2003) http://aes.missouri.edu/pfcs/research/prop402b.pdf

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