Determination of total limestone (total calcium and magnesium carbonate)
in the soil
- Introduction
The soil takes its origin from the processes of alteration of rocks, which can be both chemical, physical and biological. According to the original rocky material, soil characteristics can be different. From these characteristics we can also identify the process of plant growth. One fundamental parameter which influences the characteristics of a type of soil is its calcium carbonate content. The percentage of calcium influences the plant availability of various nutritional elements, especially phosphorum, ferrum and magnesium, as it influences the PH of soil. Soils containing calcium have a basic PH (major than 7,2).
- Objectives
These parameters are therefore useful to determine which variety of plant it is possible to cultivate in a specific type of land. Neutral soils are those with a pH close to 7. Neutral soils are the most suitable for agricultural use as most agricultural species adapt optimally to pH values between 6. 5 and 7. 5. In acidic soils the pH drops to values that compromise the mineral nutrition of the plants. On the contrary, the alkalinity of the soil is sensitive to pH values above 7. 8-8.
- Materials
-Astis Calcimeter
-1 gram of fine soil (obtained by sieving a sample of crushed soil in a mill at 2mm)
-50% hydrochloric acid solution
-Precision balance
-Flask
-Dropper pipettes
-Becker
- Products
The chemical reaction which takes place is the following:
CaCO3 + 2HCl → CaCl2 + H2O + CO2 ↑
Calcium carbonate react with hydrogen chloride to produce calcium chloride, carbon dioxide and water.
- Experimental procedure
1. Weigh 1 gram of fine soil
2. Fill the lime meter cylinder with H2O, taking care to eliminate any air present and to position the beaker intended to collect the exhaust H2O
3. Introduce fine soil into the flask
4. Take 2 ml of Hcl with the pipette and place it in the small tube attached to the calcimeter itself.
5. Place the test tube in the flask, taking care not to spill Hcl.
6. Connect the flask to the calcimeter by means of the appropriate ducts and plugs, taking care to bleed the air from the circuit.
7. After hermetically sealing the calcimeter, shake the Erlenmeyer flask causing the reaction between the Hcl contained in the tube and the soil.
8. The Hcl reacting with the calcium and magnesium carbonates present in the soil sample produces the formation of gaseous CO2 that exerts a pressure on the H2O column of the central cylinder of the calcium meter.
9. CO2 pressure causes water to escape through the drain pipe.
10. Reading on the graduated scale present in the cylinder of the calcium meter, the total percentage of calcium and magnesium carbonates present in the soil sample is obtained.
- Expected results
Calcium carbonate influences phosphoric nutrition by insolubilising phosphorus, and the higher its content in the soil, the lower the pH must be for better plant nutrition.
| Calcium carbonate valuation | |
| Useful | <5% |
| Tolerated | 5-15% |
| Volumetric footprint | 16-50% |
| Causes sterility | >50% |
| Agronomic evaluation of Calcium carbonate | |
| Absent | 0% |
| Traces | <1% |
| Slightly chalky | 1-10% |
| Averagely chalky | 11-25% |
| Very chalky | 26-50% |
| Excessively chalky | >50% |
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