SOIL pH - Alkalinity and Acidity of the soil
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Soil pH is referred to
as the "acidity" of the soil and is measured by the number of Hydrogen ions
present in the soil solution. Since S.W. Pennsylvania receives considerable rainfall
every year, and since rain is H2O, soils tend to revert back to an "acid
condition." Ammonium fertilizers also have an acidifying effect on the soil.
Soil Acidity and Alkalinity
When the soil pH is too
"acid" (low pH) or "alkaline" (high pH), nutrients present in the soil
become locked-up or unavailable. Correcting the pH has the same effect as applying
fertilizer since it "unlocks" plant nutrients already present.
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| pH |
|
Description |
| <
5.5 |
= |
Strongly
acid |
| 5.5
- 5.9 |
= |
Medium
acid |
| 6.0
- 6.4 |
= |
Slightly
acid |
| 6.5
- 6.9 |
= |
Very
slightly acid |
| 7.0 |
= |
Neutral |
| 7.1
- 7.5 |
= |
Very
slightly alkaline |
| 7.6
- 8.0 |
= |
Slightly
alkaline |
| 8.1
- 8.5 |
= |
Medium
alkaline |
| >
8.5 |
= |
Strongly
alkaline |
|
Note: this a Logarithmic Scale
based on the "powers of ten"
*
pH 6.0 is 10-times
more acidic than pH 7.0
*
pH 5.0 is
100-times
more acidic than pH 7.0
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SUMMARY
Most plants grow best within a pH
range of 6.5 to 7.2 (7 is neutral) The best way to
find out what your soil needs is by sending a sample to a soil lab. Penn State
Cooperative Extension agents sell soil test kits with instructions for your own use, or
Donnan Landscape Services can handle the soil testing for you.
The soils we've tested
in the South Hills of Pittsburgh, and Washington County, over the past 20 years, tend to
need both lime and phosphorus. The primary exception would be soils located in
"bottom ground" (near a stream or river) which usually don't require lime.
Of those soils requiring lime, dolomitic lime (high in magnesium) usually fits the test
recommendations the best.
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