Southern Regional Fact Sheet
Soil pH is one of the most important measurements of soil fertility. It indicates whether a soil could contain toxic levels of aluminum and manganese, whether it may be low in bases such as calcium and magnesium, and therefore if lime is needed. The availability of other essential plant nutrients is also affected by pH. Therefore, knowing a soilís pH may help in diagnosing nutritional problems of agricultural crops and other plants.
How soil pH is typically measured?
Most labs in the
Why does salt affect pH measurement?
A pH electrode is similar to a battery in that both of them require an electrolyte (acid/salt) to work. The amount of salt in the soil water mixture affects the pH value measured. Because the salt concentration varies in the soil by year and season, the pH values measured will also vary.
Is there a better way to measure pH?
Yes, by measuring pH in a dilute salt solution, the pH
readings will be more stable between years and during the season. Calcium
chloride can be used to simulate the salts normally present in soil. We will
use a standard amount of salt (0.01 Molar) that is slightly greater than the
amount found in
Soil pH in a typical
Why is a stable pH measurement important? Lime is
recommended for most
Will measured values of soil pH by the new method differ from the traditional method?
With the new method, soil pH readings will be lower. We have found that pH measured in calcium chloride is an average of about 0.6 units lower than when measured in water, but as noted above, it will be more consistent from year to year and within a year. The laboratory will report both salt pH and the equivalent water pH (salt pH + 0.6). The table below illustrates how equivalent water pH is calculated.
pH in calcium chloride
= Equivalent water pH
We provide this formula so that you can compare the equivalent water pH with past years results of water pH. However, the pH in calcium chloride with the new method will give stability for better comparisons across years and within a year (seasonal).
For those soils with a salt pH of 5.4 or below, the Lime
Buffer Capacity (LBC) will be measured to determine the soilís lime
requirement. The new LBC procedure is described in Southern Regional Fact Sheet
SERA-IEG-6*3 ďUniversity of
D.E. Kissel and P.F. Vendrell,