Lecture 19 Altering soil pH

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Lecture 19- Altering soil pH
Not limed
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Changing soil pH
Increasing soil pH Liming materials Calcitic
limestone CaCO3 Dolomitic limestone
CaMg(CO3)2 Quicklime CaO Hydrated lime
Ca(OH)2
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Increasing soil pH
Reaction
H Al3
2CaCO3 H2O
Ca2 Ca2
Al(OH)3 2CO2
Soil pH and base saturation are increased
Eventually, plant uptake and leaching will remove
Ca from the soil and pH and base saturation will
go back down.
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Exch. Ca2
cmol/kg
Exch. Al3
1 2 3 4 5
Years after application
Liming is a temporary fix.
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Determination of lime requirement
Must consider
1) Required change in pH- depends on plant type
2) Buffer capacity of the soil-
Note remember that as the CEC increases
the buffering capacity increases
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Determination of lime requirement
3) The chemical composition of the liming
materials
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Determination of lime requirement
4) The fineness (texture) of the liming material
The smaller the particle size, the faster the
reaction rate. In General limestone with at
least 50 of the particles small enough to pass
through a 60-mesh screen (lt0.25 mm in diameter)
are satisfactory.
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• Example problem
• How much limestone (pure CaCO3) is required to
  raise the pH of a
• Loam from pH 5 (B.S. 50) to pH 6.8 (B.S.
  90). The
• CEC equals 10 cmol/kg at pH 5.
• Calc. the cmol Ca/kg needed
• Calc. the g of Ca/kg needed
• Calc. the amount of CaCO3 needed per 1ha15cm

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Special situations
Forests- difficult application (aerial)
works best on acid, sandy soils where less lime
is needed. No-till on acid soils- lime is not
incorporated into the subsoil, must rely on
earthworms. It is a good idea to deeply
incorporate lime on acid soils before no-till
is started. Lawns, golf greens, turf grass-
incorporate lime before seeding time annual
lime additions with aeration operations.
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Decreasing soil pH
Sometimes necessary for growing acid-adapted
plants such as rhododendrons and azaleas
-addition of acid organic matter Pine
sawdust, pine needles, acid peat moss.
Note that leaves from trees such as beech and
maple may be basic and actually increase pH.
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Decreasing soil pH

• addition of Fe (FeSO4)
• Fe2 H2O O2 Fe(OH)2 H
• -adding sources of sulfur
• S O2 H2O H2SO4

FeSO4- more rapid response S more effective,
less expensive and easy to obtain