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

Abstract

Soil organic carbon (SOC) change influences the life-cycle assessment (LCA) calculations for globally traded bio-based products. Broad agreement on the importance of SOC measurement stands in contrast with inconsistent measurement methods. This paper focuses on published SOC research on lands managed for maize (Zea mays L.) in the U.S. and sugarcane (Saccharum officinarum L.) in Brazil. A literature review found that reported SOC measurement protocols reflect different sampling strategies, measurement techniques, and laboratory analysis methods. Variability in sampling techniques (pits versus core samples), depths, increments for analysis, and analytical procedures (wet oxidation versus dry combustion) can influence reported SOC values. To improve consistency and comparability in future SOC studies, the authors recommend that: (a) the methods applied for each step in SOC studies be documented; (b) a defined protocol for soil pits or coring be applied; (c) samples be analyzed at 10 cm intervals for the full rooting depth and at 20 cm intervals below rooting until reaching 100 cm; (d) stratified sampling schemes be applied where possible to reflect variability across study sites; (e) standard laboratory techniques be used to differentiate among labile and stable SOC fractions; and (f) more long-term, diachronic approaches be used to assess SOC change. We conclude with suggestions for future research to further improve the comparability of SOC measurements across sites and nations.

Remote Sensing Techniques for Soil Organic Carbon Estimation: A Review

“…Certain articles were excluded due to inadequate results justification. Considering Scopus may fail to retrieve a significant percent of related works [56], previous reviews and surveys [7,9,19,27,38,46,54,[57][58][59][60][61][62][63][64][65] were further examined for related work and references from the selected articles were also evaluated, resulting in 28 articles in total.…”

“…Hence, to optimize the monitoring and mapping capacity, there is a need for consistent datasets able to provide reliable information for SOC content estimation [8]. Despite the progress achieved in estimating SOC dynamics by means of a number of research activities and projects, there is no internationally agreed definition of a standardized soil SOC information system [9]. This is partly because proper information integration at a scale to support complex strategies and monitoring approaches has until now been difficult and expensive to setup and be operational.…”

From Laboratory to Proximal Sensing Spectroscopy for Soil Organic Carbon Estimation—A Review

“…Several studies have attempted to address this problem using machine learning techniques, in the hope that this would produce more accurate results than linear regression [27,28,42,43]. As Davis et al [16] stated, the diverse and various methodologies for SOC estimation limit the researchers' ability of the to compare the results of their studies in order to generate conclusive results. Therefore, laboratory-based studies focus on finding the most accurate and effective approach for such a calibration.…”

“…All analytical SOC measuring protocols have been thoroughly described in the literature [16], while remote sensing techniques for SOC estimation have been recently reviewed in detail [17]. However, there is a need to review the research work in laboratory and proximal sensing techniques in the VNIR-SWIR region, due to their significance on the development of nondestructive SOC estimation.…”

Growing Carbon for Sustainable and Resilient Soils

“…Gross and Harrison (2018) found that core, clod, and excavation soil‐sampling methods produce very different bulk density results and that the commonly used core method consistently led to underestimated SOC levels at soil depths greater than 20 cm. A review by Davis et.al (2018) of 41 published SOC studies on U.S. corn and Brazilian sugarcane found a lack of consistency in sampling and laboratory analysis methods used in field research that reported SOC values.…”