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Soil Acidity

Soil Acidity. Effect of pH and Aluminum on Corn Yield in PA. Soil Acidity. Active Acidity Potential Acidity. Soil Acidity. Ca ++. H +. H +. Al +++. H +. H +. Ca ++. Ca ++. Mg ++. Ca ++. K +. NH 4 +. H +. Ca ++. H +. Ca ++. Al +++. Mg ++. Mg ++. H +. Ca ++. Al +++. H +.

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Soil Acidity

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  1. Soil Acidity Effect of pH and Aluminum on Corn Yield in PA

  2. Soil Acidity • Active Acidity • Potential Acidity

  3. Soil Acidity Ca++ H+ H+ Al+++ H+ H+ Ca++ Ca++ Mg++ Ca++ K+ NH4+ H+ Ca++ H+ Ca++ Al+++ Mg++ Mg++ H+ Ca++ Al+++ H+ K+ Intensity: Active Acidity pH Quantity: Potential Acidity Buffering

  4. 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 Clay Loam CEC = 25 meq/100g Silt Loam CEC = 15 meq/100g Acidity (Limestone applied) Sandy Loam CEC = 10 meq/100g Sand CEC = 5 meq/100g pH Textbook Fig. 3.5

  5. Soil Acidity and Liming

  6. Soil Acidity • Determining exchangeable acidity • 1 eq. Base for each 1 eq. of Acidity • Titration • Add increasing amount of base measure pH change Soil pH Added Base

  7. 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

  8. Soil Acidity NOTES • 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

  9. 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 SMP Buffer Water Buffer pH Soil pH

  10. SMP Buffer Curve

  11. SMP Buffer Relationship aasl.psu.edu

  12. 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?

  13. 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

  14. 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 6.5 71240 – (10280 x SMP Buffer pH) = CaCO3/A • For pH 6.0 57840 – (8340 x SMP Buffer pH) = CaCO3/A

  15. Soil Acidity and Liming • Determining Lime requirement • Rules of thumb • For pH 7.0 Exch. Acidity (meq/100g) X 1000 = CaCO3/A • For pH 6.5 Exch. Acidity (meq/100g) X 840 = CaCO3/A • For pH 6.0 Exch. Acidity (meq/100g) X 750 = CaCO3/A

  16. 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

  17. 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-

  18. Soil Acidity and Liming • Soil Liming Reaction CaCO3→ Ca2+ + CO32- Al3+ Ca2+ Ca2+ Al3+ + H+ + Al3+ + CO32- + Ca2+ + CO32- Ca2+ H+ + Ca2+ Al3+ Ca2+ 2H2O Acid Soil Exchange Neutral Soil CO2 + 2OH- H+ + Al3+ + H2O + Al(OH)3 + Neutralization H2O

  19. Soil Acidity and Liming • Liming material quality • Calcium Carbonate Equivalent (CCE) • Neutralizing value of any liming material compared to pure calcium carbonate

  20. Soil Acidity and Liming • Calcium Carbonate Equivalent (CCE) • 1 Eq. of CaCO3 = 1 Eq. of any liming material

  21. 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.

  22. Soil Acidity and Liming • Calcium Carbonate Equivalent (CCE)

  23. 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

  24. 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

  25. 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 You have to know the form of the Ca or Mg to use these conversions! Unknown material analysis given as 23% Ca

  26. 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

  27. 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

  28. 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

  29. 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

  30. Soil Acidity and Liming Effect of aglime fineness on speed of reaction 100 Mesh Equal neutralizing value applied 7 60-80 Mesh 40-60 Mesh 6 pH 20-40 Mesh 5 8-20 Mesh No Lime 4 0 12 24 36 Reaction Time (Months)

  31. 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

  32. Soil Acidity and Liming Effect of limestone fineness on soil pH change 7 100 M 60-80 M 40-50 M 30-40 M 20-30 M 8-20 M pH 6 5 0 1 3 5 10 Tons per acre

  33. Soil Acidity and Liming Particle Size Distribution from Grinding 99.9 99 95 80 Cum. % Passing 50 20 5 0 200 100 60 40 20 8 Sieve Size (Mesh)

  34. Soil Acidity and Liming • Aglime Fineness • Pulverized Limestone • Normal ground Limestone • Granular Limestone • Coarser ground limestone • Easy spreading for homeowners • Slower to react

  35. Aglime Fineness Fineness definitions for PA Fine Sized Materials Medium Sized Materials 95% - 20 mesh sieve 90% - 20 mesh sieve 60% - 60 mesh sieve 50% - 60 mesh sieve 50% - 100 mesh sieve 30% - 100 mesh sieve Coarse sized materials - all liming materials failing to meet the above fineness criteria

  36. 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.

  37. 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

  38. 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

  39. Soil Acidity and Liming Effect of type of limestone and rate required for equal crop response 5 2-4 yr Dolomitic 4 3 Relative Lime Requirement Calcitic 2 1 0 20 40 60 80 100 % Passing 60 Mesh

  40. 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

  41. 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

  42. Less than recommended very fine limestone applied compared to normal liming program 7 6 5 pH 4 3 0 3 6 9 Reaction Time (years)

  43. Less than recommended very fine limestone applied annually but similar rate over time. 7 6 pH 5 4 0 3 6 9 Reaction Time (years)

  44. 0.8 0.6 0.4 Pellet Lime @ 0.2 500lb/A/yr Change in pH Pulverized Lime @ 0 8000 lb/A Start 1994 1995 1996 1997 -0.2 -0.4 -0.6 Soil Acidity and Liming Effect of Pellet Lime on Soil pH

  45. 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

  46. 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

  47. By-product Liming Materials • Quality • Liming value • Undesirable components

  48. 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%)

  49. Gypsum • CaSO4 • Excellent source of Ca and S • 33% Ca & 27% S • No neutralizing value • Not a liming material

  50. 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

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