Image showing a portable ion meter.

Calcium In Soil by ISE

This is a low cost laboratory method for measuring Calcium in soil. Calcium is extracted from the soil sample using sodium acetate (pH 8.2) and then directly measured using a 3041 Calcium ISE and a QP459 ION Meter

 Equipment Required

1.   QP459 ION Meter

2.   3041 Calcium Combination ISE

3.   21310 Calcium 1000ppm Standard Solution

4.   30310 Calcium  Ionic Strength Adjustment Buffer

5.   Sodium Acetate 0.5 Molar

6.   Glassware. Beakers 250ml, Volumetric Flask 100ml. 10ml pipette. Plastic Bottle.

7.   Deionised water.

 Standard Preparation

Prepare standards of 10 and 100ppm Calcium by serial dilution of the 1000ppm standard. This is achieved by pipetting 10ml of the standard into a 100ml Volumetric flask and diluting to the mark with deionized water. This is now a 100ppm Standard solution. 

Sample Preparation

Dissolve 4.1g CH3COONa with deionised water in a 1 litre volumetric flask and dilute to the mark with deionised water. This is 0.05 Molar sodium acetate.

Air dry about 10g of soil and grind to pass a 2mm sieve. Accurately weigh 4.00g of the air dried soil and add 50ml of 0.05M CH3COONa to the sample in a screw top on plastic bottle. Shake for 2 hours. Accurately pipette 10m1 of the supernatant liquid into a 100ml volumetric flask and dilute to the mark with deionised water. (It may be necessary to filter or centrifuge the sample prior to dilution).


To 100ml of each of the standards and samples add 2ml of 30310 ISAB and mix the contents. Be sure the beakers are clean and make sure not to touch the inside of the beakers with bare hands as contamination from sweat etc. is common. Beakers that have been washed with softened water or tap water will be contaminated. In these cases rinse the beakers with deionised water.

Select Calcium in the ION mode on the QP459 Ion Meter Immerse the electrode in each of the standards in increasing concentration steps in the calibration mode of the Ion Meter, rinsing the electrodes with distilled water and dabbing off the excess water between standards. 

Using the QP459 Ion meter will allow the result to be read directly on the display in ppm. It also allows for up to a 3 point calibration if required.


To express the soil calcium content in mg/100g soil multiply the concentration  by 200.

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