USDA LTAR Common Experiment measurement: Soil organic carbon stocks and change

Authors: CORDOVA, CAROLINA - University Of Nebraska; Dell, Curtis; Liebig, Mark; Cavigelli, Michel; Huggins, David; ROBERTSON, PHILIP - Michigan State University

Submitted to: Protocols.io
Publication Type: Other
Publication Acceptance Date: 6/22/2024
Publication Date: 6/22/2024
Citation: Cordova, C., Dell, C.J., Liebig, M.A., Cavigelli, M.A., Huggins, D.R., Robertson, P. 2024. USDA LTAR Common Experiment measurement: Soil organic carbon stocks and change. Protocols.io. https://dx.doi.org/10.17504/protocols.io.q26g7yo1kgwz/v1
DOI: https://doi.org/10.17504/protocols.io.q26g7yo1kgwz/v1

Interpretive Summary: NO Interpretive Summary is required for this Other 115. JLB.

Technical Abstract: The change in soil organic carbon (SOC) over time serves as an integrated indicator of carbon (C) balance in agricultural systems and as an integral metric of soil health assessments that can be carried out at all LTAR locations. While measurement of C flux with micro-meteorological methods, such as eddy-covariance, measures the exchange of carbon dioxide, methane, water, and energy flux into and out of ecosystems, these methods are expensive, requires a high level of expertise to operate, and are not applicable for plot-scale measurements. Determination of SOC concentration and soil bulk density allows calculation of the mass of SOC accumulated in the soil, and changes in SOC over time reflect system C balance. In most soils, measurable SOC changes require a minimum sampling interval of 10 or more years, depending on local factors like existing SOC stores and rotation diversity. Thus, for most cropland soils, we recommend whole profile soil cores be taken at decadal intervals, with surface soil samples perhaps taken more frequently. Whole profile samples should extend to the system’s maximum rooting depth usually into the C horizon; in most arable soils, 1 m depth will be adequate, but some locations will require deeper sampling and others shallower. We recommend minimum sample increments of 0-10, 10-25, 25-50, and 50-100 cm (or deeper / shallower as appropriate). Consistently sampling to the same depth with the same increments at known locations will greatly simplify the ability to detect small changes over decades reliably. In agricultural systems, sampling intervals should be timed to the same crop phase and at the same time of year to minimize year-to-year variability in root and residue inputs; sampling pre-planting or post-harvest can avoid fertilization recency artifacts and minimize plant disturbance and soil bulk density variability. A dry combustion CN analyzer should be used to measure total C; for soils with detectable carbonate minerals, inorganic C must first be removed by acid fumigation or analyzed independently for later subtraction. Estimation of SOC stocks can be calculated using two methods: spatial coordinate (includes bulk density), and equivalent soil mass (normalized mass per unit area).