Proximal sensing for soil carbon accounting

Abstract

Abstract. Maintaining or increasing soil organic carbon (C) is vital for securing food production and for mitigating greenhouse gas (GHG) emissions, climate change, and land degradation. Some land management practices in cropping, grazing, horticultural, and mixed farming systems can be used to increase organic C in soil, but to assess their effectiveness, we need accurate and cost-efficient methods for measuring and monitoring the change. To determine the stock of organic C in soil, one requires measurements of soil organic C concentration, bulk density, and gravel content, but using conventional laboratory-based analytical methods is expensive. Our aim here is to review the current state of proximal sensing for the development of new soil C accounting methods for emissions reporting and in emissions reduction schemes. We evaluated sensing techniques in terms of their rapidity, cost, accuracy, safety, readiness, and their state of development. The most suitable method for measuring soil organic C concentrations appears to be visible–near-infrared (vis–NIR) spectroscopy and, for bulk density, active gamma-ray attenuation. Sensors for measuring gravel have not been developed, but an interim solution with rapid wet sieving and automated measurement appears useful. Field-deployable, multi-sensor systems are needed for cost-efficient soil C accounting. Proximal sensing can be used for soil organic C accounting, but the methods need to be standardized and procedural guidelines need to be developed to ensure proficient measurement and accurate reporting and verification. These are particularly important if the schemes use financial incentives for landholders to adopt management practices to sequester soil organic C. We list and discuss requirements for developing new soil C accounting methods based on proximal sensing, including requirements for recording, verification, and auditing.

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

“…The most frequent statistical indicators are RMSE, RPD, and R 2 . It should be noted that the error should be referred to using the same units as those of the analyzed soil property [146]; most studies do not use the same evaluation methods, as shown in Tables 1 and 2. In addition to that, the normalization of the data due to skewness makes it even harder to compare studies.…”

How to measure, report and verify soil carbon change to realize the potential of soil carbon sequestration for atmospheric greenhouse gas removal

“…Standardization of reference laboratory methods, spectral measurements and soil data exchange to some extent negates these issues, and they are addressed in several international co‐operations, one of which is Pillar 5 of the Global Soil Partnership (GSP, ). If standardization and calibration transfer challenges can be solved, combining spectral libraries can provide a vast data resource for not only local but also more regional and global SOC analyses (England & Viscarra Rossel, ; Viscarra Rossel, Behrens, et al, ; Viscarra Rossel, Brus, Lobsey, Shi, & Mclachlan, ).…”

“…A method used in a number of set‐ups is gamma attenuation. This can be measured on the extracted soil core (England & Viscarra Rossel, ; Lobsey & Viscarra Rossel, ) or directly in the soil (Jacobs, Eelkema, Limburg, & Winterwerp, ). With this technique, the attenuation by matter of gamma radiation originating from a small radioactive source is measured over a known volume between source and detector.…”

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.…”