Soil Acidity and Liming Soil Acidity and Liming Fundamentals of Nutrient Management Training Course Dec, 2005 Louis McDonald Division of Plant and Soil Sciences West Virginia University

Benefits of Liming Acid Soils Reduces metal ion toxicities (esp. Al 3+ ) Reduces metal ion toxicities (esp. Al 3+ ) Improves soil physical condition Improves soil physical condition Stimulates microbial activity Stimulates microbial activity Symbiotic nitrogen fixation Symbiotic nitrogen fixation Increases CEC Increases CEC Supplies Ca (and Mg) Supplies Ca (and Mg) Increases P and Mo availability Increases P and Mo availability Increases water and nutrient use efficiency Increases water and nutrient use efficiency

Overview Nature of soil acidity Nature of soil acidity Factors affecting response to lime Factors affecting response to lime How lime recommendations are made – and – what we can do about improving them How lime recommendations are made – and – what we can do about improving them

Soil pH – Soil Acidity – Liming pH pH The negative logarithm of the hydrogen ion activity The negative logarithm of the hydrogen ion activity -log(H + ) -log(H + ) < 7 = acidic < 7 = acidic > 7 = basic > 7 = basic A property of a (soil) solution A property of a (soil) solution

Soil pH – Soil Acidity – Liming Soil Acidity Soil Acidity Soils = Solid Phase + Soil Solution Soils = Solid Phase + Soil Solution Al 3+ H+H+ SolidSolution Al 3+ H+H+ As part of the solution acidity is neutralized, some of the solid phase acidity replaces it - Buffering As part of the solution acidity is neutralized, some of the solid phase acidity replaces it - Buffering

Soil pH – Soil Acidity – Liming Soil Acidity = Solid Acidity + Solution Acidity Soil Acidity = Solid Acidity + Solution Acidity Active Acidity Potential Acidity Exchangeable (salt-replaceable) Exchangeable (salt-replaceable) Titrateable (residual) Titrateable (residual)

Soil pH – Soil Acidity – Liming Liming Liming A practice to reduce soil acidity (potential + active) A practice to reduce soil acidity (potential + active)and Raise soil (solution) pH to some target value (range) Raise soil (solution) pH to some target value (range)

Why are soils acid? H + and Al 3+ H + and Al 3+ Al 3+ is the most important form Al 3+ is the most important form H + is unstable on soil surfaces H + is unstable on soil surfaces Dissolves solid and converts to Al form Dissolves solid and converts to Al form

Aluminum saturation decreases as soil pH increases. In most soils, little or no Al toxicity is observed above pH 5.0 – 5.5 (From Havlin et al., 1999).

Why do soils acidify? Increases in exchangeable Al Increases in exchangeable Al Mineral weathering Mineral weathering Loss of exchangeable Ca, Mg Loss of exchangeable Ca, Mg Rainfall > ET Rainfall > ET Removal by crops Removal by crops

Why do soils acidify? Increases in H + (= exchangeable Al) Increases in H + (= exchangeable Al) Nitrification Nitrification Acidification depends on fate of NO 3 Acidification depends on fate of NO 3 Taken up by plant = some acidification Taken up by plant = some acidification Denitrified = net alkalinity Denitrified = net alkalinity Leached with base cations = maximum acidification Leached with base cations = maximum acidification Precipitation of Ca and Al phosphates from P-containing fertilizers Precipitation of Ca and Al phosphates from P-containing fertilizers

Why do soils acidify? Increases in H + (= exchangeable Al) Increases in H + (= exchangeable Al) Organic matter decomposition Organic matter decomposition CO 2, soluble organic acids CO 2, soluble organic acids Plant uptake of nutrient ions (depends on harvesting Plant uptake of nutrient ions (depends on harvesting PlantSoil SolutionPlantSoil Solution K+K+ H+H+ OH - NO 3 -

Soil pH Regulation? Acid soils (pH < ~ 5.5) Acid soils (pH < ~ 5.5) Base saturation low Base saturation low Ca, Mg, etc. lost by leaching Ca, Mg, etc. lost by leaching Aluminum buffered systems (Al-hydrolysis) Aluminum buffered systems (Al-hydrolysis) After pH 5.5, [Al] very low After pH 5.5, [Al] very low

Soil pH Regulation Normal agricultural soils (pH 5.5 – 7.5) Normal agricultural soils (pH 5.5 – 7.5) Starting to see appreciable base saturation Starting to see appreciable base saturation pH buffered by ion exchange pH buffered by ion exchange Alkaline soils Alkaline soils Free carbonates Free carbonates Mg 2+ Ca H + Mg 2+ H + + Ca 2+

Liming Materials Purpose is to neutralize acidity Purpose is to neutralize acidity Calcium carbonate Calcium carbonate Calcitic limestone Calcitic limestone Dolomitic limestone Dolomitic limestone etc. etc. Acid generating reaction Acid generating reaction Acid neutralizing reaction Acid neutralizing reaction

Why do we call it ‘liming’ when we’re not applying lime? CaCO 3 = limestone rock Ca(OH) 2 = slaked or hydrated lime CaO = lime (burned lime) CaCO 3 = softcrushed heat water CO 2

Factors Affecting Lime Response Purity Purity Particle size Particle size Moisture Content Moisture Content

Purity Expressed as Calcium Carbonate Equivalents (CCE) or Neutralizing Value (NV) Expressed as Calcium Carbonate Equivalents (CCE) or Neutralizing Value (NV) CaCO 3 (MW = 100 g/mole) is the standard, NV = 100 CaCO 3 (MW = 100 g/mole) is the standard, NV = 100

Purity What is the NV of MgCO 3 ? What is the NV of MgCO 3 ? Both neutralize the same amount of H + Both neutralize the same amount of H + But, MgCO 3 “weighs” less? But, MgCO 3 “weighs” less? MW MgCO 3 = 84 g/mole MW MgCO 3 = 84 g/mole Therefore, 1 kg or lb of MgCO 3 neutralizes more acid than an equal mass of CaCO 3 Therefore, 1 kg or lb of MgCO 3 neutralizes more acid than an equal mass of CaCO 3

Purity How much more = Neutralizing Value How much more = Neutralizing Value General Formula General Formula Specific Formula Specific Formula In practice determined experimentally In practice determined experimentally

Typical Calcium Carbonate Equivalents (CCE) for some common liming materials. Liming Material Typical CCE (%) Pure calcite 100 Calcitic limestone 75 – 100 Dolomitic limestone 75 – 108 Aragonite 95 – 100 Hydrated lime 120 – 136

Particle Size Limestone is relatively insoluble Limestone is relatively insoluble Effective only when dissolved Effective only when dissolved Dissolution is a surface controlled reaction Dissolution is a surface controlled reaction Surface area per unit mass (specific surface) increases as particle size decreases Surface area per unit mass (specific surface) increases as particle size decreases Therefore, dissolution rate increases as particle size increases Therefore, dissolution rate increases as particle size increases

Particle size decreases as Sieve No. increases. U.S. Sieve No. Opening Size (mm) U.S. Sieve No. Opening Size (mm)

Potash and Phosphate Institute

Effect of particle size and limestone type on clover yields. Crimson Clover Yield (DW/pot) Particle Size (mesh) CalciticDolomitic 20 – – – < (in Barber, 1984)

Quantifying effects of particle size Efficiency Factors and Efficiency Ratings Efficiency Factors and Efficiency Ratings Sieve size Efficiency Factor % of Material Efficiency Rating < – – > %64%

Moisture Content Purchased by weight Purchased by weight Correct for % moisture Correct for % moisture

Effective Calcium Carbonate Equivalence (ECCE) Quantitatively account for purity, particle size, moisture Quantitatively account for purity, particle size, moisture ECCE=CCE x ER x % Moisture ECCE=CCE x ER x % Moisture Lime Rate = Recommended Rate Lime Rate = Recommended Rate ECCE X 100

Establishing a Liming Program Lime requirement of the crop Lime requirement of the crop Can neutralize to some pH or Al saturation Can neutralize to some pH or Al saturation Grasses, alfalfa = higher pH Grasses, alfalfa = higher pH Blueberries, azaleas, potatoes = lower pH Blueberries, azaleas, potatoes = lower pH Rotation considerations Rotation considerations Texture and organic matter content Texture and organic matter content Coarse textured, low OM soils will have lower LR Coarse textured, low OM soils will have lower LR

Soil texture & cation exchange capacity effects on limestone application rate – soil pH relationships. (From Havlin et al., 1999)

Establishing a Liming Program Timing Applications Timing Applications Interactions with phosphorus Interactions with phosphorus

P Concentration in soil solution as affected by different Ca(OH) 2 and Ca(H 2 PO 4 ) 2 rates and sequence of these chemicals to the soil. L 0, L 1, L 2, L 3, L 4 refer to increasing rates of Ca(OH) 2. (From Soltanpour et al. 1974)

Establishing a Liming Program Frequency of Applications Frequency of Applications Need to apply 3 – 6 months before planting Need to apply 3 – 6 months before planting More frequent, lower applications for lighter textured soils More frequent, lower applications for lighter textured soils Depth of tillage Depth of tillage Could be based on 6”, 7”, or 8” plow depths. Could be based on 6”, 7”, or 8” plow depths. Need to know what your lab is using Need to know what your lab is using If plowing deeper or shallower, need to adjust accordingly If plowing deeper or shallower, need to adjust accordingly

Lime Rates or Lime Recommendations Incubation Lab determination of the relationship between lime rate and resulting soil pH Lab determination of the relationship between lime rate and resulting soil pH Field Calibration A field experiment to scale the lab results There’s been a reasonable amount of research on lime incubations, but relatively little on field calibrations

Lime Incubations

Because Because Limestone is insoluble Limestone is insoluble Equilibrium is slow Equilibrium is slow Soil Test labs need to analyze thousands of samples Soil Test labs need to analyze thousands of samples Lime recommendations normally based on ‘Quick Tests’ Lime recommendations normally based on ‘Quick Tests’

Lime Quick Tests Based on soil pH in a buffer Based on soil pH in a buffer SMP – Shoemaker-McLean-Pratt SMP – Shoemaker-McLean-Pratt AE – Adam-Evans AE – Adam-Evans Mehlich Mehlich Using buffer pH (and sometimes soil pH), make a lime recommendation Using buffer pH (and sometimes soil pH), make a lime recommendation

Desired pH Soil + Buffer pH pH = 6.5 pH = Lime requirement to achieve various soil pH levels for an 8” plow layer

Review Soil pH is H +, soil acidity is Al 3+ Soil pH is H +, soil acidity is Al 3+ A ‘natural’ process that can be accelerated by management A ‘natural’ process that can be accelerated by management Easily remedied with lime applications Easily remedied with lime applications Source, purity, particle size, moisture content Source, purity, particle size, moisture content Crops, rotations, tillage depth, frequency, timing Crops, rotations, tillage depth, frequency, timing

What can we do to improve lime recommendations 1. Emphasize ‘maintenance’ lime applications Time Soil pH Critical pH w/o Lime Optimal pH

What can we do to improve lime recommendations? 2. Recognize that a soil test recommendation is for an ‘average’ soil Use our best judgment and experience to make adjustments Use our best judgment and experience to make adjustments Encourage on-farm experimentation Encourage on-farm experimentation

What can we do to improve lime recommendations 3. Make recommendations for specific regions and/or soils Are there ways to group soils in the state? 50+ named soils 50+ named soils 7 soil orders 7 soil orders 5 MLRAs 5 MLRAs

What can we do to improve lime recommendations? I need soils from around the state – the more the better I need soils from around the state – the more the better a Gilpin from every county a Gilpin from every county I’ll take anything you know the name of I’ll take anything you know the name of County, MLRA County, MLRA A ‘pasture’ sample A ‘pasture’ sample ~top 3 inches ~top 3 inches About 1 gallon About 1 gallon I’ll arrange to get it I’ll arrange to get it (304) 293 – 6023 x4324 (304) 293 – 6023 x4324