Soil Acidity

Soil AcidityEffect of pH and Aluminum on Corn Yield in PA

Soil Acidity

• Active Acidity

• Potential Acidity

Soil Acidity

Ca++

Mg++ K+

H+

Al+++

NH4+

Ca++

Ca++

Ca++

Ca++

Ca++

Ca++

Al+++

Mg++Mg++

Al+++

H+

K+

H+

H+H+

H+

H+

H+

Quantity:Potential Acidity

Intensity:Active Acidity

pHBuffering

Soil Acidity• Soil Acidity Buffering

– Soils tend to buffer pH• High clay and/or organic matter greater buffering • Low clay and/or organic matter lower buffering

pH

Aci

dity

(Lim

esto

ne a

pplie

d)

Clay Loam

CEC = 25 meq/100g

Silt Loam

CEC = 15 meq/100g

Sandy Loam

CEC = 10 meq/100g

Sand

CEC = 5 meq/100g

Textbook Fig. 3.5

Soil Acidity and Liming

Soil Acidity• Determining exchangeable acidity

– 1 eq. Base for each 1 eq. of Acidity– Titration

• Add increasing amount of base measure pH change

Added Base

Soi

l pH


– Buffer pH• Add a pH buffer solution and measure pH change• Known relationship between pH change and change

in acidity• Common pH buffers

– SMP (used in PA)» Triethanolamine» Paranitrophenol» Potassium chromate» pH 7.5

– Adams-Evans– Mehlich – Woodruff


– Buffer pH• Add a pH buffer solution and measure pH change• Known relationship between pH change and change

in acidity• Common pH buffers

– SMP (used in PA)» Triethanolamine» Paranitrophenol» Potassium chromate» pH 7.5

– Adams-Evans– Mehlich - Many states including PA going to this – Woodruff

NOTES

Soil pH & Buffer pH

H+ H+

H+

H+H+ H+

H+

H+

H+

H+H+H+

H+

H+

H+

H+

H+H+

H+H+

H+ H+H+H+

H+

H+ H+H+

H+

H+H+

H+H+

Soil pH Buffer pH

WaterSMP Buffer

SMP Buffer Curve

5

5.5

6

6.5

7

7.5

8

0 0.2 0.4 0.6 0.8 1

Acidity (meq H+)

Buf

fer p

H

SMP Buffer RelationshipBuffer pH Exch. Acidity

(meq/100g)Lime Rec.For pH 6.5

(lb/A)7.0 2 06.8 3 20006.6 4 30006.4 7 50006.2 9 80006.0 11 100005.8 14 120005.6 16 140005.4 19 16000

aasl.psu.edu

Soil Acidity and Liming• Determining Lime requirement

– Exchangeable Acidity• 1 meq. Base/100g for each 1 meq. of Acidity/100g• How many pounds of lime do we need per acre?

Soil Acidity and Liming• Determining Lime requirement

– Desired pH• Acid sensitive crops pH 7.0

• Most crops and soils pH 6.5

• Highly weathered soils pH 5.5

• Acid loving crops 5.5 - 6.0


• Determining Lime requirement– Based on target pH and Exchangeable acidity

Formulas used by PSU AASL• For pH 7.0

84500 – (12180 x SMP Buffer pH) = CaCO3/A

• For pH 6.571240 – (10280 x SMP Buffer pH) = CaCO3/A

• For pH 6.057840 – (8340 x SMP Buffer pH) = CaCO3/A


• Determining Lime requirement– Rules of thumb

• For pH 7.0Exch. Acidity (meq/100g) X 1000 = CaCO3/A




• Liming Materials– Material that will neutralize soil acidity

• Calcium Oxide (CaO)– Lime, burnt lime, quick lime

• Calcium Hydroxide (Ca(OH)2)– Hydrated lime, slaked lime

• Calcium Carbonate (CaCO3)– Calcitic limestone

• Calcium/Magnesium Carbonate (Ca,MgCO3)– Dolomitic limestone

Soil Acidity and Liming• For each equivalent of acidity we need to apply 1

equivalent of liming material• Chemical neutralizing ability of liming materials

– Equivalents of OH- produced by the reaction of the liming material.

• Ca(OH)2 → Ca2+ + 2 OH-

• CaCO3 + H2O → Ca2+ + 2 OH- + CO2

• CaO + H2O → Ca2+ + 2 OH-

• CaSiO3 + H2O → Ca2+ + HSiO3- + OH-

• CaSO4 → Ca2+ + SO42-

Soil Acidity and Liming• Soil Liming Reaction

Al3+

Al3+

Al3+

H++ Ca2+ + CO3

2-

Ca2+

Ca2+

Ca2+

Ca2+

Ca2+

+ H+ + Al3+ + CO32-

CO2

2H2O+

+

2OH-

H2O

+

H+ + Al3+ +H2O + Al(OH)3

CaCO3 → Ca2+ + CO32-

Exchange

Neutralization

Acid Soil

Neutral Soil

Soil Acidity and Liming• Liming material quality• Calcium Carbonate Equivalent (CCE)

– Neutralizing value of any liming material compared to pure calcium carbonate


• Calcium Carbonate Equivalent (CCE)– 1 Eq. of CaCO3 = 1 Eq. of any liming material

Soil Acidity and Liming• Calcium Carbonate Equivalent

– Example: MgCO3

MgCO3 = 84 g/mole or 42 g/ eq.CaCO3 = 100 g/mole or 50 g/ eq.

Soil Acidity and Liming• Calcium Carbonate Equivalent (CCE)

Material % CCECaCO3 100

MgCO3 119

(Ca,Mg)CO3 109

CaO 179Ca(OH)2 136

CaSiO3 86

Common Limestones 80 - 100

Soil Acidity and Liming• Soil test recommendations are made as lb CCE/A• Adjust if CCE is different from 100%

– Example: • Recommendation = 2000 lb CCE/A• Hydrated Lime Ca(OH)2 CCE = 136%

• Required amount of liming material = 100 x Rec. CCE/A % CCE of Material

Soil Acidity and Liming• Real World

– Not usually dealing with pure materials, so we can't always calculate the CCE

– Measure CCE in lab – Required in most states• Titration with standard acid

– CCE is provide on the label for all liming materials sold in PA

– Be careful calculating CCE on unknown materials

Estimating Neutralizing Value of Liming Materials

- Be very careful -• Ca x 2.5 = CaCO3

• Mg x 3.5 = MgCO3

• MgCO3 x 1.19 = CaCO3

• MgO x 2.5 = CaCO3

• CaO x 1.79 = CaCO3

Unknown material analysis given as 23% Ca

You have to know the form of the Ca or Mg to use these conversions!

Estimating Neutralizing Value of Liming Materials

- Be very careful -

• If you don’t know what the material is made of then you need to measure the CCE directly!

• Cost ~ $10-15

Soil Acidity and Liming• Calcium Oxide Equivalent (COE)

– Neutralizing value of any liming material compared to pure calcium Oxide

– 1 Eq. of CaO = 1 Eq. of any liming material

– 1 Eq. wt. of CaO = 1 Eq. wt. of any liming material

COE = eq. wt. CaO/ eq. wt. Liming material

COE = 28/ eq. wt. Liming material


• Soil test recommendations may be made as lb COE/A

• Adjust if COE is different from 100%

• Required amount of liming material = 100 x Rec. COE/A % COE of Material


• Physical fineness of liming materials– Fineness determines speed of reaction– The finer limestone is ground the faster it will

react

– Fineness given as % passing specific screen mesh sizes


7

6

5

4

pH

0 12 24 36Reaction Time (Months)

100 Mesh

60-80 Mesh

40-60 Mesh

20-40 Mesh

8-20 Mesh

No Lime

Equal neutralizing value applied

Effect of aglime fineness on speed of reaction


• Physical fineness of liming materials

– Practical Limits to fineness

– Larger than 20 mesh – not effective

– Smaller than 100 mesh – little added benefit


7

6

5

pH

0 1 3 5 10

Tons per acre

100 M

60-80 M

40-50 M

30-40 M

20-30 M

8-20 M

Effect of limestone fineness on soil pH change


200 100 60 40 20 805

205080

99.99995

Sieve Size (Mesh)

Cum

. % P

assi

ng

Particle Size Distribution from Grinding


• Aglime Fineness – Pulverized Limestone

• Normal ground Limestone

– Granular Limestone• Coarser ground limestone • Easy spreading for homeowners• Slower to react

FineSized Materials

MediumSized Materials

95% - 20 mesh sieve

60% - 60 mesh sieve

50% - 100 mesh sieve

Coarse sized materials - all liming materials failing to meet the above fineness criteria

Aglime Fineness Fineness definitions for PA

90% - 20 mesh sieve

50% - 60 mesh sieve

30% - 100 mesh sieve

Aglime Quality

• Acid-Base Chemistry and Fineness

• CaCO3 + H2O Ca2+ + H2CO3 + 2OH-

2OH- + 2H+ 2H2O

For a given amount of acidity an equivalent amount of base (liming material) will be required regardless if it is ground very fine.

Aglime Quality

•Acid-Base Chemistry in soils

1 meq/100g acidity in the soil

will require 1 meq/100g of

CaCO3 to neutralize it.

1 meq CaCO3/100g soil =

1000 lb CaCO3/A


• Aglime Fineness – No matter how fine you grind limestone you

cannot increase the chemical neutralizing ability

– Finer the better, because it will react faster, but there are practical limitations

– Distribution in “Fine Size” Limestone – usually adequate for practical liming for field crops

– Little difference between calcite and dolomite


5

4

3

1

Rel

ativ

e Li

me

Req

uire

men

t

0 20 40 60 80 100% Passing 60 Mesh

2

Dolomitic

Calcitic

2-4 yr

Effect of type of limestone and rate required for equal crop response


• Pellet Lime – Finely ground limestone– Glued together into water soluble pellets– Advantage: Handling, spreading, speed of

reaction– Disadvantage: Cost

100-200 mesh


• Fluid Lime – Finely ground limestone– Suspended in water with clay– Approx. 1000 lb CCE/ton material– Advantage: Spreading, speed of reaction– Disadvantage: Cost

Less than recommended very fine limestone applied compared to normal

liming program

7

6

5

4

pH

0 3 6 9Reaction Time (years)

3

Less than recommended very fine limestone applied annually but

similar rate over time.

7

6

5

4

pH

0 3 6 9Reaction Time (years)


-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

Start 1994 1995 1996 1997Cha

nge

in p

H

Pellet Lime @500lb/A/yrPulverized Lime @8000 lb/A

Effect of Pellet Lime on Soil pH

Soil Acidity and Liming• Calcium and Magesium

– Normal liming practices will also supply required calcium and magnesium

• At normal rates usually adequate Ca will be supplied for most crops

• Magnesium will depend on the type of limestone used

– If Mg is required use a Mg containing limestone (dolomitic)– Mg recommendations

» pounds Mg/A» % Mg in recommended limestone

Calcium and Magnesium

• Management Recommendations– Maintain optimum pH – Maintain at least optimum levels of Mg (60

ppm) and K (100 ppm)– Don’t worry about ratios until they are way

out of balance• eg. Mg:Ca >1, K:Mg>1• Rare

By-product Liming Materials

• Quality–Liming value

–Undesirable components

Example: Liming Value

Material sold in western PA for $2/ton

CCE = 5.38%

For 1 ton of neutralizing value:

2000 X 100 ÷ 5.38 = 37,174 lbs. or 18.6 tons ($37.20)

Fineness:Through 20 Mesh = 98.8% (90%)

Through 60 Mesh = 78.2 % (60%)

Through 100 Mesh = 63.2% (50%)

Gypsum

• CaSO4

• Excellent source of Ca and S– 33% Ca & 27% S

• No neutralizing value• Not a liming material

Limestone vs Gypsum • Limestone changes pH Gypsum doesn’t

• Both are good sources of Ca

– Lime to recommended pH . . . no need for additional Ca for the

soil or for agronomic crops in PA

– High pH but low calcium soils (Sodic Soils) use gypsum as a

source of Ca for the soil and the crop (Western US)

• Improves physical properties Relieves chemical compaction

– Low pH, acid loving crops or highly weathered soils, use

gypsum as a source of Ca for the soil and the crop (Tropics)

• Minimal lime to reduce Al toxicity

Byproduct Materials Undesirable components

• Should be registered (PDA)• Must be approved for land application by DEP

– May limit lifetime application• Problem with unregistered materials and

materials from out of state– May be little or no checking of quality

• Determine the source– Dust, screenings– Stainless steel slag

• Ask what contaminants might be present • If in doubt . . . get it analyzed OR don’t use it

Example: Undesirable components - Metals in Aglime

Material Cu Zn Pb Cr Ni Cd

Aglime .02 .03 .05 .02 .04 .00

Aglime .02 .02 .05 .02 .04 .00

Aglime .03 .02 .04 .02 .04 .00

Aglime .01 .05 .07 .02 .04 .00

Aglime .01 .05 .07 .02 .04 .00

Ind. Byprod. .04 .05 .10 .03 .07 .00

Ind. Byprod. .04 .08 .20 .04 .05 .00

Ind. Byprod. .03 .00 .07 .03 .05 .00

Ind. Byprod. .03 .27 .09 .04 .08 .00

Ind. Byprod. .02 5.62 .08 .02 .06 .01

Ind. Byprod. 68 160 19 2037 435 5

Other Materials

• Biosolids and Water Treatment Sludges– Often have significant neutralizing value

– Must be clean

– Must be registered if sold as liming materials

Other MaterialsOrganic Calcium Compounds

• Promesol 30, Liquid Lime– Trihydroxy glutaric acid 25%

Ca– 1 gallon = 500-750 lb CCE?

• Liqui-Til– Trihydroxy glutaric acid– Neutralizes pH in alkaline

soil?

• KK Organic Soil Builder– Neutralizes both acidic and

alkaline soils?

• Liqui-Cal– 8% Ca– 1 gallon = 500 lb CaCO3?

• Liquid Calcium– 1 gallon = Ca in 500 lb CaCO3?– Suggest it is a lime substitute

• Golden Cal– Glucoheptomic acid– 1 gallon = 500 lb CCE?

• pH Plus– 1 gallon = 500-750 lb CCE?

Other Materials

• Remember: 1 Eq. of base is required to neutralize 1 Eq. of acid

• Watch out for materials that contain Ca with unwritten or suggestive claims for liming value

Soil Acidity and Liming• Limestone Application

– Apply limestone far enough ahead of time to be effective

– Spread limestone uniformly• Spinner spreaders• Boom spreaders• Damp lime• Dust

– Spit high rates of limestone (>4 ton/A)– Time of year is not too critical

• Consider soil quality issues – compaction– Mix limestone as much as practical

• Adjust for depth of mixing - 6 2/3 in. standard depth• No till – Correct pH before going to no-till


4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

85 86 87 88 89 90 91 92 93 94 95 96 97

0-2"2-4"4-6"

Time (years)

Soil pH vs No-Till With 6000 lbs/A of Lime Applied Every 3rd Year

Documents

Soil Acidity