Choosing the right number of Soil Samples

Regrow's Soil Sampling Workflow can help you decide on the right number of soil samples for your project. Here's how.

Soil sampling is a crucial part of any carbon project, ensuring accurate carbon sequestration estimates. However, soil sampling can be expensive, and determining the right number of samples can be challenging. Regrow's Soil Sample Estimation feature provides suggested sample numbers to help balance budget constraints with scientific rigor. This allows you to make informed decisions based on your project needs. If you already have a specific sample number or budget in mind, you do not need to use this feature. Instead, you can specify the total number of samples you want to take to your CSM and the Sample Design will take it into account.

How can Regrow's Soil Sampling Workflow help?

Soil sampling can be costly, and taking unnecessary samples can strain your budget. However, the more samples taken, the more representative and predictive the data is likely to be for your entire project. Regrow's Soil Sample Design can suggest different sample size estimates specific to your project boundary so you can choose the best fit for your project, taking into account both cost efficiency and representation of the soil properties present. The estimation feature offers flexibility, allowing you to align your soil sampling strategy with your budget, project requirements, and risk tolerance.

How it works

Before you can use the Soil Sample Estimation feature, the fields in the project should be finalized (Enrollment is closed). Then, the Soil Sampling Workflow stratifies the fields in the project and evaluates the soil properties, field conditions and climate factors to provide three sample count suggestions. You can then choose the option that best aligns with your project’s financial and scientific requirements. Once a sample count has been chosen, it will be used to generate a Soil Sample Design for your project.

Sample Estimation Options

1. Variance-based estimate for the project

This approach focuses on estimating the average Soil Organic Carbon (SOC) across all fields and provides the lowest sample number recommendation. The calculation is based on statistical variance, using the standard deviation of SOC measurements across the entire project area. The goal is to ensure that the margin of error, with 90% confidence, does not exceed 5% of the mean SOC value of all the fields. This method is most suitable for budget-conscious projects. However, in some regions where soil variability is higher, such as Europe, this approach may underestimate the necessary sample size, as it assumes relatively uniform SOC distribution across fields. Regrow doesn't recommend taking fewer samples than this.

2. Stratified variance-based estimate

This method is similar to the first option, but refines the approach by accounting for differences in SOC within distinct strata. By dividing the project into strata based on similar soil properties, region and climate, average SOC estimates are more specific to the group of fields within each stratum. Each stratum is analyzed individually, ensuring that the margin of error for each grouping of fields remains within 5% of the mean at a 90% confidence level. This approach balances cost and uncertainty. It aims for a more representative sample distribution compared to the variance-based approach, particularly in areas with diverse soil conditions, or projects that are spread out geographically. This option is most suitable for most projects.

3. Area-based estimate

This method follows conservative industry standards, creating a sampling density of one sample per 1.6 hectares (4 acres). It's based on recommendations from scientific studies and widely accepted protocols, such as those referenced in carbon credit methodologies. This approach provides the highest number of samples, resulting in the most comprehensive and predictive sampling plan. While it may be more expensive, it ensures the highest level of confidence in SOC estimates, making it ideal for projects prioritizing accuracy and long-term data reliability.

This method is particularly useful for projects undergoing strict third-party verification or those seeking to establish long-term soil health benchmarks. However, it is important to note that this option results in the largest number of samples suggested. For most projects, this option will likely not be a reasonable sample count due to the cost.

Choosing the right sample count

Selecting the appropriate sample estimate depends on your project’s priorities. It is important to note that you are not limited to one of these three options—you may also select a sample number that falls between the suggested estimates based on your specific needs and constraints.

Once you have reviewed the suggested estimates, select the one that best fits your needs or choose a number in between the suggested options. Let your Customer Success Manager know of your final selection so they can initiate the sample plan generation.