Geoscience Reference
In-Depth Information
pH range
5.5 or lower
Highly acid
5.6-6.0
Moderately acid
6.1-6.9
Mildly acid
Neutral
7.0
7
Mildly alkaline
7.1-7.7
7.8-8.3
Moderately alkaline
8.4 or higher
Highly alkaline
Figure 3
The pH scale as related to soil. (
Soil Sense
C-03)
(1) pH in water (pHw)
A measured quantity of dried and sieved soil is shaken for one hour with a
measured quantity of pure water (usually one part soil to five parts water), mixed
well and then tested. The results using this method more closely ref lect current soil
conditions than the calcium chloride method and therefore the actual pH to which
plant roots are exposed at that point in time.
(2) pH in calcium chloride (pHCaCl
2
)
A measured quantity of soil is mixed with a measured quantity of a standard
calcium chloride solution, shaken for one hour, and tested. The readings given by
this method are usually lower than the water method by 0.5-1.0 pH units, but
more reliably predict the likely response to lime treatment.
In low salinity soils the pH in water will measure 0.6-1.2 pH units more than
the pH in calcium chloride. In high salinity soils, the readings will be much closer,
typically a 0.1-0.5 pH unit difference. The calcium chloride method shows less
seasonal variability than the water method and is a useful diagnostic measurement
as soils can be sampled at any time during the year and more confidently
compared with previous results.
What do the results mean?
There are a number of things to consider when interpreting soil test figures for pH:
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