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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Representative Results
  • Discussion
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

The verification method described here is adaptable for monitoring pedogenic inorganic carbon sequestration in various agricultural soils amended with alkaline earth metal silicate-containing rocks, such as wollastonite, basalt, and olivine. This type of validation is essential for carbon credit programs, which can benefit farmers that sequester carbon in their fields.

Abstract

The present study aims to demonstrate a systematic procedure for monitoring inorganic carbon induced by enhanced weathering of comminuted rocks in agricultural soils. To this end, the core soil samples taken at different depth (including 0-15 cm, 15-30 cm, and 30-60 cm profiles) are collected from an agriculture field, the topsoil of which has already been enriched with an alkaline earth metal silicate containing mineral (such as wollastonite). After transporting to the laboratory, the soil samples are air-dried and sieved. Then, the inorganic carbon content of the samples is determined by a volumetric method called calcimetry. The representative results presented herein showed five folded increments of inorganic carbon content in the soils amended with the Ca-silicate compared to control soils. This compositional change was accompanied by more than 1 unit of pH increase in the amended soils, implying high dissolution of the silicate. Mineralogical and morphological analyses, as well as elemental composition, further corroborate the increase in the inorganic carbon content of silicate-amended soils. The sampling and analysis methods presented in this study can be adopted by researchers and professionals looking to trace pedogenic inorganic carbon changes in soils and subsoils, including those amended with other suitable silicate rocks such as basalt and olivine. These methods can also be exploited as tools for verifying soil inorganic carbon sequestration by private and governmental entities to certify and award carbon credits.

Introduction

CO2 is a major greenhouse gas (GHG), and its concentration in the atmosphere is increasing continuously. Preindustrial global average CO2 was about 315 parts per million (ppm), and as of April 2020, the atmospheric CO2 concentration increased to over 416 ppm, hence causing global warming1. Therefore, it is critical to reduce the concentration of this heat-trapping GHG in the atmosphere. Socolow2 has suggested that to stabilize the concentration of atmospheric CO2 to 500 ppm by 2070, nine 'stabilization wedges' will be required, where each stabilization wedge is an indiv....

Protocol

1. Soil sampling method and core collection

  1. Divide the mapped and a demarcated agricultural land area of interest into different plots based on the land elevation, historical crop yield, and/or land management strategy. Determine the leveling of each plot using a GPS receiver, classify crop yield based on historical farm records (below-average, average, above-average), and the land management strategy used for each plot (types of soil amendments used, if any). Place the flags at the boundaries of each plot to.......

Representative Results

The SIC content of soils can be determined using various methods, including an automated carbon analyzer or a calcimeter. The automated carbon analyzer for total soil carbon determination measures the CO2 pressure built-up in a closed vessel30. In calcimetry, the evolved volume of CO2 released after acidification, typically by the addition of concentrated HCl acid, of the carbonate-containing sample is measured. The calcimetry method is relati.......

Discussion

Given that collecting samples from fertilized agricultural fields is usually difficult, it is suggested that samples should be collected before nutrient application. It is also advisable to avoid collecting samples from frozen fields. The sampling depth may vary in different areas depending on the ease of sampling over the vertical profile, and the depth of the water table. The selected soil sampling device is dependent on the soil structure and depth of interest33. While it is more convenient to .......

Acknowledgements

This work was supported by a Food from Thought Commercialization Grant, which is funded from the Canada First Research Excellence Fund. Canadian Wollastonite provided industrial financial support as part of this Grant.

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Materials

NameCompanyCatalog NumberComments
Analytical scaleSartoriusQuintix 224-S1Four decimals.
CalcimeterEijkelkampModel 08.53To determine the wt% CaCO3-equivalent in the sample.
Drying cabinet/muffle furnaceThermo ScientificF48055-6050°C or 103 ± 2°C.
HClFisher ScientificA144S-500Reagent grade (36.5%-38.0%).
HNO3Fisher ScientificT003090500Trace metal analysis grade (69.0%-70.0%)
Inductively Coupled Plasma Mass Spectrometer (ICP-MS)PerkinElmerNexIONTo determine the concentration of Ca in the microwave-digested soil.
Microwave digesterPerkinElmerTitanTo digest soils in concentrated HNO3.
pH meterOakton700Calibrated with standard solutions before each set of measurements; temperature corrected to 25 °C.
Scanning Electron Microscope -Energy Dispersive Spectroscope (SEM-EDS)OxfordX-Max20 SSDTo determine the morphology of soil particulates.
Sieve shakerRetschAS-200For soil fractionation.
Soil auger samplerEijkelkamp01-16Depths down to 700 cm.
Soil Dakota probe samplerJMCPN139Depths down to 100 cm.
Soil probe samplerJMCPN031Depths down to 30 cm.
Soil moisture meterExtechMO750Measure moisture content up to 50%
Wavelength Dispersive X-ray Fluorescence spectroscope (WDXRF)Malvern PanalyticalZetiumTo characterize elemental composition of soil.
X-ray Diffraction analyzer (XRD)PanalyticalEmpyreanTo characterize mineralogicalbproperties of soil.

References

  1. Trends in atmospheric carbon dioxide. NOAA Available from: https://www.esrl.noaa.gov/gmd/ccgg/trends/ (2020)
  2. Socolow, R. Wedges reaffirmed. Bulletin of the Atomic Scientists. 2011 (9), (2011).
  3. Mission Innovation. Joint launch state....

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Pedogenic Inorganic CarbonWeatheringSilicate MineralsAgricultural SoilsCarbon SequestrationNegative Emission Carbon CreditEnhanced WeatheringSoil SamplingSoil MoistureSoil AnalysisCarbon Content

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