Determination of organic c in soil (walkey-black method)
The Walkey-Black method is a commonly used method for the determination of organic carbon in soil. Here is an overview of the procedure:
1. Sample Preparation: Collect a soil sample from the desired location and air-dry it. Remove any visible plant material, rocks, or debris from the sample. Crush the soil to a fine powder using a mortar and pestle.
2. Acid Oxidation: Weigh out 0.5g of the soil sample and place it in a digestion tube. Add 5ml of concentrated sulfuric acid (H2SO4) to the tube and allow it to stand for at least 30 minutes. Then, add 0.05g of potassium dichromate (K2Cr2O7) to the tube.
3. Steam Distillation: Attach a condenser to the digestion tube and heat the mixture in a water bath for at least 2 hours. The organic carbon in the soil sample will be oxidized to carbon dioxide (CO2) and will be trapped in a solution of sodium hydroxide (NaOH) in a receiving flask.
4. Titration: After distillation is complete, titrate the solution in the receiving flask with standardized hydrochloric acid (HCl) to determine the amount of carbon dioxide that was released during the oxidation process.
5. Calculation: The amount of carbon dioxide released during the oxidation process is proportional to the amount of organic carbon in the soil sample. Use the volume of hydrochloric acid used in the titration to calculate the organic carbon content in the soil sample.
It is important to note that the Walkey-Black method is a relatively simple and cost-effective method for the determination of organic carbon in soil. However, it may not provide the most accurate results compared to more sophisticated analytical techniques. It is important to carefully follow the protocol and use proper safety precautions when performing this method.