Liming Materials

Ch 9.8

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

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 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

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