Measurement of Calcium in Soil

Introduction

All plants need calcium rich soil to grow. The calcium is used by the plant in developing the plant cell walls and membranes. Furthermore, it is a non-leaching mineral (it will stay in the soil) and will improve water penetrability and reduce soil salinity. It is thus helpful to determine the amount of calcium contained in soil. Generally, Atomic Absorption Instruments (AA) or Inductivity Coupled Plasma-Optical Emission Spectrometry Instruments (ICP-OES) are used to measure the amount of calcium ions present in soil. An easier method involves extracting the calcium ion from sample soils with 1 mol/L ammonium acetate (CH₃COONH₄), and then by using the handy and affordable LAQUAtwin calcium ion meter B-751. The LAQUAtwin Ca²⁺ meter is used as a quick check to determine the calcium content of soil.

Method

1. Dry the soil for about a week, and sift it using a 2mm diameter net sieve.
2. Place 1g of test soil in 100ml glass beaker and add the 20ml of 1mol/L CH₃COONH₄ to the beakers.
3. Shake the beakers (amplitude 40m/min, speed 250rpm) for 1 hour to extract Ca²⁺ from the soil using a laboratory shaker (Recipro Shaker SR-IIW made by Taiyo Kagaku Kogyo Company of Japan).
4. Filter the liquid through JIS No.6 filter paper.
5. Calibrate LAQUAtwin B-751 with 150mg/L and 2000mg/L Ca²⁺ standard solutions which contain the same concentration of CH₃COONH₄ as in the filtered samples. (Do not use the standard solutions packed with the instrument)
6. A small sample of the filtered solution is placed on the sensor of the LAQUAtwin Ca²⁺ and measured. To repeat sampling, wash with tap water and pat dry with a paper tissue.

Results and Benefits

The use of accurate calcium ion testing in controlling the calcium content of soil ensures that the plants which are grown in the soil are given the necessary minerals and can easily absorb water. The table below shows that the results given by the LAQUAtwin Ca²⁺ pocket meter are comparable to those from Inductivity Coupled Plasma-Optical Emission Spectrometry Instruments (ICP-OES).

 The LAQUAtwin Ca²⁺ pocket meter is small and compact; convenient to carry around in your pocket for quick on-site testing. Its easy-to-use interface is simple for anyone to use the LAQUAtwin Ca²⁺ pocket meter.