Measuring soil carbon is an important step for assessing soil fertility, sustainability of agroecosystems and participation in carbon farming programs. There are several methods, from laboratory analyses to rapid field tests, that can determine the level of organic carbon in soils.
The most accurate way to measure organic carbon is the dry combustion method. In this method, a soil sample is heated to 900 °C in an elemental analyzer and the amount of carbon dioxide released is measured. The results are expressed as a percentage of carbon by weight of the sample. This method requires sample preparation: sieving, drying and pulverizing, and measuring the bulk density of the soil to calculate the carbon content per unit area .
For those looking for more affordable methods, there is the chemical oxidation method of Walkley and Black. This is based on the oxidation of organic carbon using chemicals and provides a rough estimate of carbon content. However, this method is less accurate and may not account for all organic carbon, especially in soils with high carbon content.
Modern technology offers alternative approaches. For example, spectroscopic methods can estimate carbon content without the need for extensive sampling. Portable spectroscopic probes, such as those developed by Yard Stick, use light beams to analyze soil composition in situ. These techniques can significantly reduce analysis time and costs, although they require calibration and may be less accurate under certain conditions .
The following approach is recommended for practical measurement of soil carbon:
- Sampling: Use a drill to collect soil from a depth of 0-10 cm. Take several samples from different parts of the field to obtain a representative sample.
- Sample preparation: Sieve the soil through a 2 mm mesh sieve, dry at room temperature and pulverize to a homogeneous mass.
- Analysis: Send the prepared samples to the laboratory for analysis by dry combustion or use available chemical tests for preliminary evaluation.
- Interpretation of results: Compare data with regional regulations or historical data to assess changes in carbon content.
Regular measurement of soil carbon content allows monitoring the effectiveness of agronomic practices to improve the fertility and sustainability of agroecosystems. The choice of method depends on the resources available, the accuracy required and the objectives of the study.
