pH

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Soil pH Test:

 

Purpose:  to determine if the soil is acidic or basic.  The pH is a measure of the hydrogen ion concentration expressed in logarithmic terms.  The pH values decrease as the hydrogen ion concentration increases and range from 0 to 14.  Values below 7.0 are acidic, values above 7.0 are alkaline, and 7.0 is neutral.  For each unit change in pH there is a 10-fold change in acidity or alkalinity (i.e. pH 6.0 is ten times more acidic than pH 7.0, and pH 5.0 is a hundred time more acidic than 7.0).  

 

Tools:  the following procedure used the LaMotte garden soil test kit model EM, Code 5934.  Other methods of measuring pH are also possible.  Some test kits are more accurate than others.  Before using a particular “quick test “method, compare it to laboratory results.  The tests recommended in this handbook have all been compared to KSU soil test laboratory results, and have been deemed satisfactory for initial screening purposes.

 

Procedure:

 

1)  Fill the test tube in the LaMotte kit to line 4 with pH Indicator solution.  Squeeze the bottle gently to control the amount dispensed.

 

2)  Use the 0.5 g spoon to add 3 measures of soil sample.

 

3)  Cap and shake gently for one minute.

 

4)  Allow tube to stand for 10 minutes to let soil settle.

 

5)  Match color reaction with the pH color chart.  Record the result as pH on the data sheet.

 

Interpretation:  Soil pH is generally considered adequate if it is between 6 and 7.  On some Kansas soils, the natural pH is 7 or even 8, and good crops are grown on these soils.  A soil with a pH higher than 8 merits further testing, however, to see if other factors may limit crop growth (for example salt), and whether soil amendments or special adapted crops should be grown.  The primary concern with pH is if it drops too low, through the use of fertilizers or other products.  The soil pH can be raised through the addition of lime, and lowered (for specialty crops like blueberries) with sulfur.  See KSU bulletins on these topics for more information.

 

For the pH values on your data sheet, rate your soils according to the scoring table below.  This is similar to the scoring system used in the River Friendly Farms notebook.  A score-card sheet may be found in Appendix C along with blank data sheets.

 

4

3

2

1

Soil pH is between 6.5 and 6.8.

Soil pH is between 6 and 7.2.

Soil pH is between 5.8 and 8.0.

Soil pH is lower than 5.8 or higher than 8.0.