Soil organic carbon sequestration, storage, retention and loss in U.S. croplands: Issues paper for protocol development

Review of Soil Organic Carbon Measurement Protocols: A US and Brazil Comparison and Recommendation

“…Comparisons of management practice effects on soil C were generally made using a synchronic approach with paired plots or a chronosequence (i.e., diachronic approach), with the most common design being paired plots [65,66]. We also found that the majority of the studies reviewed were sampled only once during the course of the experiment [67,68].…”

“…Spatial variability and the slow rate at which C changes both present major challenges for monitoring and predicting SOC changes [105]. Long-term field experiments (i.e., a diachronic approach) lasting several years or even decades are generally considered to be the best for detecting soil management effects on soil C storage [67], but unfortunately paired plots (i.e., synchronic or chronosequence studies) were found to be the most common within the literature reviewed for both countries. One study by Costa Junior [106] did examine both strategies and showed that the diachronic approach could more accurately detect soil C accumulation changes since the synchronic approach tended to over-estimate C accumulation.…”

“…Measuring SOC only within the upper portion of the soil profile could yield inaccurate results [67], and either over-or under-estimate temporal changes such as erosion that occurred [113]. As a result, most SOC sampling protocols (e.g., GRACEnet) now advise that samples be taken to a depth of at least 100 cm [11,62].…”

The science of variable climate and agroecosystem management

“…These authors specify that changes in SOC levels as a result of management practices (e.g., tillage) must result in greater SOC stock than the pretreatment baseline SOC levels in the same land unit and result in a net depletion of atmospheric CO 2 . Thus, claims of SOC sequestration must evidence atmospheric CO 2 transferred into the soil humus through land unit plants, plant residues, and other organic solids (Olson 2013;Olson et al 2014a). Olson et al (2014b) offer several recommendations congruent with Kladivko et al (2014) and Necpalova et al (2014) papers: (1) protocols for measuring SOC sequestration should be standardized; (2) sequestration rates over a period of time should be measured and compared to the pretreatment baseline over regular intervals during the study; and (3) external already stored C inputs into the land unit must be accounted for to assure SOC sequestration and SOC net gain, i.e., SOC is sequestered or stored in the land unit from the atmosphere rather than redistributed from previous stores in another land unit.…”

Data management approach to multidisciplinary agricultural research and syntheses

“…The establishment and use of standard sampling methodologies across research sites and personnel helps to minimize variations, ensure scalability, and allows for transparent management of data. The worth and value of standard methods in agricultural research has been recognized, and there is great potential for more widespread utilization (Hunt et al 2001;Olson 2013;White et al 2013). Team protocols have helped to ensure consistency in data collected among sites; accountability of data originating from each site; and a consistent set of data for systems analysis and predictive modeling across a suite of local, regional, and national scale models.…”