Agriculture Reference
In-Depth Information
Table 14.4 Raising soil pH guidelines: quantities
of calcium carbonate* (g/m 2 of ground chalk or
limestone*) required to raise soil to pH 6.5
Soil pH can be lowered by the addition of sulphur
which is converted to sulphuric acid by soil micro-
organisms. The amount of sulphur required
depends on essentially the same factors as for lime
requirement: the pH change needed and the soil
texture, that is, more is required for clay soils to have
the same effect as on sandy soils.
Acid fertilizers such as ammonium sulphate reduce
soil pH over a period of years in outdoor soils, such as
on lawns. They can also be used in liquid feeding to
offset the tendency of hard water to raise pH levels in
composts.
Starting pH
Soil texture
Light soils
'Loams'
Heavy soils
(very high clay
content)
5.0 1,000 1,200 1,400
5.5 700 800 1,000
6.0 400 500 600
* If using hydrated lime, these application rates should be
reduced by a quarter.
(very sandy, low
clay)
Note that even fine lime needs to be added many
months in advance to achieve the pH required for
the plants to be grown. The amount of lime to add
depends on:
X fi nal soil pH to be achieved (normally raised to
pH 6.5)
X soil pH from which it is to be lifted (as found in the
soil test)
X texture of the soil (it is the clay content that resists
the effect of lime)
X strength of the lime used ('neutralizing value')
X fi neness of the lime.
Further reading
14
Brown, L.V. (2008) Applied Principles of Horticulture .
3rd edn. Butterworth-Heinemann.
Cresser, M.S. (1993) Soil Chemistry and Its
Applications . Cambridge University Press.
Ingram, D.S. et al (eds) (2008) Science and the
Garden . 2nd edn. Blackwell Science.
Pratt, M. (2005) Practical Science for Gardeners .
Timber Press.
Please visit the companion website for further information:
www.routledge.com/cw/adams
 
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