liming materials ch 9.8. agricultural limes carbonate forms calcite (caco 3 ) dolomite (camgco 3 )...
TRANSCRIPT
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
Reactions in the Soil
1) Reaction with Carbon Dioxide
CaCO3 + H2O + CO2 → Ca(HCO3)2
2) Reaction with Soil ColloidsColloid(H+,Al3+) + 2Ca(HCO3) → Colloid(2Ca2+)+Al(OH)3 + H2O+4CO2
Overall ReactionColloid(H+,Al3+) + 2CaCO3+ H2O→ Colloid(2Ca2+)+ Al(OH)3 +2CO2Results 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
0
50
100
150
200
250
6 5.5 5 4.5 4
Sand
Loam
Clay
Lbs/
1000
ft2
lime
to a
pply
Soil pH
Lbs CaCO3 needed to raise pH to 6.5
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)
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
4 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
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 analysis multiplication factor
> 8 mesh 0
8 – 20 mesh 0.2
20-60 mesh 0.6
< 60 mesh 1.0
Example Calculation – fineness factor
pan
60
20
8
100 g16 g x 0 = 0
22 g x 0.2 = 4.4
35 g x 0.6 = 21.0
27 x 1.0 = 27.0
Fineness Factor = 4.4 + 21.0 + 27.0 = 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 = 60-69 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