Soil Acidity Effect of pH and Aluminum on Corn Yield in PA
Dec 30, 2015
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 AciditypH
Buffering
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
(Li
mes
tone
app
lied)
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
Soil Acidity• Determining exchangeable acidity
– 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
Soil Acidity• Determining exchangeable acidity
– 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+)
Bu
ffer
pH
SMP Buffer RelationshipBuffer pH Exch. Acidity
(meq/100g)Lime Rec.
For pH 6.5
(lb/A)
7.0 2 0
6.8 3 2000
6.6 4 3000
6.4 7 5000
6.2 9 8000
6.0 11 10000
5.8 14 12000
5.6 16 14000
5.4 19 16000aasl.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
Soil Acidity and Liming
• 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
Soil Acidity and Liming
• Determining Lime requirement– Rules of thumb
• For pH 7.0Exch. Acidity (meq/100g) X 1000 = CaCO3/A
• For pH 6.5Exch. Acidity (meq/100g) X 840 = CaCO3/A
• For pH 6.0Exch. Acidity (meq/100g) X 750 = CaCO3/A
Soil Acidity and Liming
• 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
Soil Acidity and Liming
• 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 % CCE
CaCO3 100
MgCO3 119
(Ca,Mg)CO3 109
CaO 179
Ca(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 Acidity and Liming
• 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
Soil Acidity and Liming
• 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
Soil Acidity and Liming
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
Soil Acidity and Liming
• Physical fineness of liming materials
– Practical Limits to fineness
– Larger than 20 mesh – not effective
– Smaller than 100 mesh – little added benefit
Soil Acidity and Liming
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
Soil Acidity and Liming
200 100 60 40 20 8
0
5
20
50
80
99.9
99
95
Sieve Size (Mesh)
Cum
. % P
assi
ng
Particle Size Distribution from Grinding
Soil Acidity and Liming
• 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
Soil Acidity and Liming
• 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
Soil Acidity and Liming
5
4
3
1
Rel
ativ
e L
ime
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
Soil Acidity and Liming
• Pellet Lime – Finely ground limestone– Glued together into water soluble pellets– Advantage: Handling, spreading, speed of
reaction– Disadvantage: Cost
100-200 mesh
Soil Acidity and Liming
• 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)
Soil Acidity and Liming
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
Start 1994 1995 1996 1997Ch
ange
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
Soil Acidity and Liming
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