DOI: 10.5061/dryad.p2ngf1w06
title: Data from: The importance of accounting method and sampling depth to estimate changes in soil carbon stocks

description: 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 (&gt; 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.
description: This data is comprised of two different datasets. The first
 dataset comes from University of California, Davis’ Century Experiment at
 the Russel Ranch Sustainable Agriculture Facility (38°32′24″N,
 121°52′12″W). The second dataset comes from UW Madison’s Wisconsin
 Integrated Cropping Systems Trial (WICST) at the UW Madison Agricultural
 Research Station in Arlington, WI (43°18″N, 89°20″W). Data were previously
 published in Sanford et al. (2012) (https://doi.org/10.1016/j.agee.2012.08.011) and Tautges et al. (2019) (https://doi.org/10.1111/gcb.14762). To explore management impacts on soil carbon accrual over time. See these publications for details on data collection. All datasets were cleaned to remove any missing values and organized for input into the SimpleESM R function (https://github.com/fabienferchaud/SimpleESM). SimpleESM requires an excel input document with bulk density (g cm<sup>-3</sup>) and carbon concentration (g kg<sup>-1</sup>) data. Bulk density ("BD")and carbon concentration ("Concentrations") are recorded on separate sheets. Each sheet contains a campaign variable (year in which the sample was taken), treatment (ID of experimental treatment), block (ID of experimental block),  plot (ID of sampled plot), point (ID of sampled point), and the lower depth and upper depth (in centimeters) of the sample.
description: # Data from: The importance of accounting method and sampling depth to
 estimate changes in soil carbon stocks
 [https://doi.org/10.5061/dryad.p2ngf1w06](https://doi.org/10.5061/dryad.p2ngf1w06) ## Description of the data and file structure This dataset contains 3 different excel files: WICST data, UC Davis Century Maize treatments, and UC Davis Century Wheat treatments. Each file contains the following sheets: * Readme: contains a summary of the content, a description of all column names, and a table that matches the original treatment name (used in the excel document) to the corresponding treatment name used in Raffeld et al. (2024) * Original_data: Original, unedited data from WICST and UC Davis Century experiment, used in Sanford et al. (2012) and Tautges et al. (2019), respectively. * BD: Contains bulk density measurements by treatment, plot, point, depth, and year. * Concentrations: Contains carbon concentration measurements by treatment, plot, point, depth, and year. * Any "NA" values indicate missing data. ## Sharing/Access information Data was derived from the following sources: * The Wisconsin Integrated Cropping Systems Trial At the University of Wisconsin-Madison. Data obtained from Sanford et al. (2012): [https://doi.org/10.1016/j.agee.2012.08.011](https://doi.org/10.1016/j.agee.2012.08.011 "Persistent link using digital object identifier") * University of California-Davis Century Experiment. Data obtained from Tautges et al. (2019): [https://doi.org/10.1111/gcb.14762](https://doi.org/10.1111/gcb.14762) ## Code/Software Equivalent soil mass and fixed depth stocks can be calculated using the SimlpleESM R function. The data presented here is ready for use in the SimpleESM function. Download of the function can be found here: [https://github.com/fabienferchaud/SimpleESM?tab=readme-ov-file](https://github.com/fabienferchaud/SimpleESM?tab=readme-ov-file). Details on how to use the function can be found here: [https://hal.science/hal-04013158](https://hal.science/hal-04013158).