The importance of accounting method and sampling depth to estimate changes in soil carbon stocks
Abstract Background As interest in the voluntary soil carbon market surges, carbon registries have been developing new soil carbon measurement, reporting, and verification (MRV) protocols. These protocols are inconsistent in their approaches to measuring soil organic carbon (SOC). Two areas of conce...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
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BMC
2024-01-01
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| Series: | Carbon Balance and Management |
| Subjects: | |
| Online Access: | https://doi.org/10.1186/s13021-024-00249-1 |
| _version_ | 1797340376284004352 |
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| author | Anna M. Raffeld Mark A. Bradford Randall D. Jackson Daniel Rath Gregg R. Sanford Nicole Tautges Emily E. Oldfield |
| author_facet | Anna M. Raffeld Mark A. Bradford Randall D. Jackson Daniel Rath Gregg R. Sanford Nicole Tautges Emily E. Oldfield |
| author_sort | Anna M. Raffeld |
| collection | DOAJ |
| description | Abstract Background As interest in the voluntary soil carbon market surges, carbon registries have been developing new soil carbon measurement, reporting, and verification (MRV) protocols. These protocols are inconsistent in their approaches to measuring soil organic carbon (SOC). Two areas of concern include the type of SOC stock accounting method (fixed-depth (FD) vs. equivalent soil mass (ESM)) and sampling depth requirement. Despite evidence that fixed-depth measurements can result in error because of changes in soil bulk density and that sampling to 30 cm neglects a significant portion of the soil profile’s SOC stock, most MRV protocols do not specify which sampling method to use and only require sampling to 30 cm. Using data from UC Davis’s Century Experiment (“Century”) and UW Madison’s Wisconsin Integrated Cropping Systems Trial (WICST), we quantify differences in SOC stock changes estimated by FD and ESM over 20 years, investigate how sampling at-depth (> 30 cm) affects SOC stock change estimates, and estimate how crediting outcomes taking an empirical sampling-only crediting approach differ when stocks are calculated using ESM or FD at different depths. Results We find that FD and ESM estimates of stock change can differ by over 100 percent and that, as expected, much of this difference is associated with changes in bulk density in surface soils (e.g., r = 0.90 for Century maize treatments). This led to substantial differences in crediting outcomes between ESM and FD-based stocks, although many treatments did not receive credits due to declines in SOC stocks over time. While increased variability of soils at depth makes it challenging to accurately quantify stocks across the profile, sampling to 60 cm can capture changes in bulk density, potential SOC redistribution, and a larger proportion of the overall SOC stock. Conclusions ESM accounting and sampling to 60 cm (using multiple depth increments) should be considered best practice when quantifying change in SOC stocks in annual, row crop agroecosystems. For carbon markets, the cost of achieving an accurate estimate of SOC stocks that reflect management impacts on soils at-depth should be reflected in the price of carbon credits. |
| first_indexed | 2024-03-08T10:01:12Z |
| format | Article |
| id | doaj.art-d5143262ba974fe6a1ab4607523bb467 |
| institution | Directory Open Access Journal |
| issn | 1750-0680 |
| language | English |
| last_indexed | 2024-03-08T10:01:12Z |
| publishDate | 2024-01-01 |
| publisher | BMC |
| record_format | Article |
| series | Carbon Balance and Management |
| spelling | doaj.art-d5143262ba974fe6a1ab4607523bb4672024-01-29T10:56:21ZengBMCCarbon Balance and Management1750-06802024-01-0119112010.1186/s13021-024-00249-1The importance of accounting method and sampling depth to estimate changes in soil carbon stocksAnna M. Raffeld0Mark A. Bradford1Randall D. Jackson2Daniel Rath3Gregg R. Sanford4Nicole Tautges5Emily E. Oldfield6Environmental Defense FundThe Forest School, Yale School of the Environment, Yale UniversityDepartment of Plant and Agroecosystem Sciences, University of Wisconsin-MadisonNatural Resources Defense CouncilDepartment of Plant and Agroecosystem Sciences, University of Wisconsin-MadisonMichael Fields Agricultural InstituteEnvironmental Defense FundAbstract Background As interest in the voluntary soil carbon market surges, carbon registries have been developing new soil carbon measurement, reporting, and verification (MRV) protocols. These protocols are inconsistent in their approaches to measuring soil organic carbon (SOC). Two areas of concern include the type of SOC stock accounting method (fixed-depth (FD) vs. equivalent soil mass (ESM)) and sampling depth requirement. Despite evidence that fixed-depth measurements can result in error because of changes in soil bulk density and that sampling to 30 cm neglects a significant portion of the soil profile’s SOC stock, most MRV protocols do not specify which sampling method to use and only require sampling to 30 cm. Using data from UC Davis’s Century Experiment (“Century”) and UW Madison’s Wisconsin Integrated Cropping Systems Trial (WICST), we quantify differences in SOC stock changes estimated by FD and ESM over 20 years, investigate how sampling at-depth (> 30 cm) affects SOC stock change estimates, and estimate how crediting outcomes taking an empirical sampling-only crediting approach differ when stocks are calculated using ESM or FD at different depths. Results We find that FD and ESM estimates of stock change can differ by over 100 percent and that, as expected, much of this difference is associated with changes in bulk density in surface soils (e.g., r = 0.90 for Century maize treatments). This led to substantial differences in crediting outcomes between ESM and FD-based stocks, although many treatments did not receive credits due to declines in SOC stocks over time. While increased variability of soils at depth makes it challenging to accurately quantify stocks across the profile, sampling to 60 cm can capture changes in bulk density, potential SOC redistribution, and a larger proportion of the overall SOC stock. Conclusions ESM accounting and sampling to 60 cm (using multiple depth increments) should be considered best practice when quantifying change in SOC stocks in annual, row crop agroecosystems. For carbon markets, the cost of achieving an accurate estimate of SOC stocks that reflect management impacts on soils at-depth should be reflected in the price of carbon credits.https://doi.org/10.1186/s13021-024-00249-1Bulk densityCarbon accountingCarbon stocksFixed depthEquivalent soil massCarbon markets |
| spellingShingle | Anna M. Raffeld Mark A. Bradford Randall D. Jackson Daniel Rath Gregg R. Sanford Nicole Tautges Emily E. Oldfield The importance of accounting method and sampling depth to estimate changes in soil carbon stocks Carbon Balance and Management Bulk density Carbon accounting Carbon stocks Fixed depth Equivalent soil mass Carbon markets |
| title | The importance of accounting method and sampling depth to estimate changes in soil carbon stocks |
| title_full | The importance of accounting method and sampling depth to estimate changes in soil carbon stocks |
| title_fullStr | The importance of accounting method and sampling depth to estimate changes in soil carbon stocks |
| title_full_unstemmed | The importance of accounting method and sampling depth to estimate changes in soil carbon stocks |
| title_short | The importance of accounting method and sampling depth to estimate changes in soil carbon stocks |
| title_sort | importance of accounting method and sampling depth to estimate changes in soil carbon stocks |
| topic | Bulk density Carbon accounting Carbon stocks Fixed depth Equivalent soil mass Carbon markets |
| url | https://doi.org/10.1186/s13021-024-00249-1 |
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