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 1) Reaction with Carbon Dioxide CaCO 3 + H 2 O + CO 2 → Ca(HCO 3 ) 2 2) Reaction with Soil Colloids Colloid(H +,Al 3+ ) + 2Ca(HCO 3 ) → Colloid(2Ca 2+ )+Al(OH) 3 + H 2 O+4CO 2 Overall Reaction Colloid(H +,Al 3+ ) + 2CaCO 3 + H 2 O→ Colloid(2Ca 2+ )+ Al(OH) 3 + 2CO 2 Results in an increase in base saturation, and a corresponding increase in pH

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

Effect of Soil pH and Soil Texture Lbs/1000 ft 2 lime to apply Soil pH Lbs CaCO 3 needed to raise pH to 6.5

Chemical composition Commonly expressed as CaCO 3 equivalent (CCE)  chemical purity of material  Chemical equivalency Moles of + or – charge per mole of ion or compound Standard is CaCO 3 = 2 equivalents/mole Ca +2 = Mg +2 = CaO =Ca(OH)2=MgO=CaCO3=MgCO3 CaMg(CO 3 ) 2 = 2 Ca 2+ (4 equivalents/mole)

Calculating Chemical Equivalency Example: CaO (2 equivalents/mole)  CaO=56 g/mole, equivalent weight = 28 g/mole  CaCO 3 =100 g/mole, equivalent weight = 50 g/eq CCE= (50/28) x 100 = 178.6% 100 lb CaO will neutralize as much acidity as lbs CaCO 3 !!! Try with dolomite CaMg(CO 3 ) 2 (M.W.=184.4) CCE = [50 /(184.4/4)] x 100 = equivalents/mole

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

8 openings /inch 20 openings /inch 60 openings /inch

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

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

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

Calculating fineness factor Sieve analysismultiplication factor > 8 mesh0 8 – 20 mesh mesh0.6 < 60 mesh 1.0

Example Calculation – fineness factor pan g 16 g x 0 = 0 22 g x 0.2 = g x 0.6 = x 1.0 = 27.0 Fineness Factor = = 52.4

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 = and 80-89

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

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

Effectiveness of Aglime in no-till and conventional tillage systems on clay soil Stevens and Dunn(2003)