Measurement and Monitoring Soil Carbon

How much will it cost?

Producing estimates and maps of SOC is not cheap. It will only make sense to go ahead if the benefits outweigh costs. The actually costs will depend on context but here we give some guidelines and tools to estimate the costs that you will incur. Main components of cost are summarized in Table 1.

Table 1. Components of costs. Cost of items marked * are strongly dependent on the number of samples taken

Stage	Includes	Cost for measuring totals	Cost for mapping
Planning and managing the process	Planning all work Acquiring background data Finding suitable staff Monitoring and quality assurance	Low	Low
Field data collection	Equipment Skilled and unskilled staff (*) Transport and field allowances (*)	High	Higher as more samples needed
Laboratory measurement	Soil sample preparation (*) Measuring carbon content by traditional (*) or spectral methods	High using traditional methods Low using spectral methods	High using traditional methods Low using spectral methods
Data handling	Prepare data capture forms and/or software. Organizing databases Entering and checking data (*)	Low	Higher
Data analysis	Statistical calculations	Low	High
Reporting and using results	Reporting Interpreting	Low	Modest

As shown in the above table, the number of samples required has an important influence on several cost components. The number of samples that need to be taken from a project area depends on many factors including:

1. whether totals or maps are required,

2. the level of variability of SOC within in the target area,

3. the required levels of precision of the results

The cost of measuring SOC depends on the number of samples, costs of sampling, and laboratory prices. In some cases the cost of demonstrating the change in carbon stocks in soils to the required accuracy and precision may exceed the benefits that accrue from the increase in stocks (IPCC, 2003; MacDicken, 1997). Thus, developing alternative cheaper and repeatable measures is a research priority. Infrared spectroscopy offers promise for a rapid, reliable and cost effective measurement of soil organic carbon. Large parts (87%) of the costs of soil analysis is personnel. Compared to the conventional thermal oxidation method, soil spectroscopy can reduce laboratory costs of measuring carbon by about 56%. However, there is no significant difference in the total cost of measuring SOC between the thermal oxidation and the infrared spectroscopy when a small number of soil samples are used. This is because a large proportion of the costs of soil carbon measurement are incurred for soil sampling and preparation compared with laboratory costs. With increasing number of soil samples, however, the total cost of carbon measurement using infrared spectroscopy is cheaper than using the conventional method. Infrared spectroscopy may also be the only practical way to measure carbon concentrations in large numbers of soil samples.

Benefits of soil measurement can often be justified due to the additional benefits of obtaining information on other soil properties and constraints (soil fertility, soil physical properties), which can be predicted from the infrared spectral measurement.

Cost–error analyses 

According to the Marrakesh Accords, uncertainties in measuring greenhouse gases in offsetting projects should be quantified. Estimation errors, model errors, and sampling errors associated with the number of samples are among the major sources of uncertainties in measuring SOC. IPCC (2003) has recommended using confidence intervals as quantitative estimate of uncertainty.

To estimate the sample size required to measure carbon stocks with the desired confidence interval (e.g. 95%), it is necessary to know the mean and standard deviation of carbon stocks from previous studies or from a new reconnaissance survey.