4.7 Article

Assessing a VisNIR penetrometer system for in-situ estimation of soil organic carbon under variable soil moisture conditions

Journal

BIOSYSTEMS ENGINEERING
Volume 224, Issue -, Pages 197-212

Publisher

ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.biosystemseng.2022.10.011

Keywords

VisNIR spectroscopy; soil organic carbon; penetrometer; soil carbon sequestration; external parameter; orthogonalisation

Funding

  1. USDA-NIFA-AFRI foundational program
  2. [2017-67021-26248]
  3. [2018-67007-28529]

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Soils are important carbon sinks, and accurately measuring and estimating soil organic carbon content is a challenge. In this study, a visible and near-infrared penetrometer system was developed to measure in-situ soil spectra, and a spectral library and regression models were used to estimate soil organic carbon content. The External Parameter Orthogonalisation transformation removed the interference of soil moisture and other factors. The results showed that the penetrometer system can rapidly and cost-effectively measure soil organic carbon content.
Soils are one of the main terrestrial carbon sinks and contain more carbon than the combined total in the atmosphere and terrestrial vegetation. A major challenge is quantifying how much carbon is stored in the soil and how much it has been sequestered due to changed management practices. In this study, a visible and near-infrared (VisNIR) penetrometer system was developed to measure in-situ soil VisNIR reflectance spectra to a depth of 90 cm into the soil profile. A spectral library of VisNIR soil spectra collected in airdry and ground states were used to calibrate Cubist regression models for estimating soil organic carbon (SOC) contents. The External Parameter Orthogonalisation (EPO) transformation was applied to the in-situ spectra to remove soil moisture and other in-situ effects from the spectra. This penetrometer system was used to estimate SOC contents at three sites on three different days under variable soil moisture states. The penetrometer EPO performed better compared to the EPO constructed from moist cores. After applying EPO transformation matrix, soil wetness did not have any influence on soil SOC content estimations. The SOC contents were estimated using the in-situ VisNIR system were validated against lab-measured SOC content with mean R2, RMSE, and bias of 0.88, 0.32%, and 0.15%, respectively. It is concluded that the VisNIR penetrometer can potentially be used to measure SOC content rapidly and cost-effectively in-situ with a fine depth resolution.(c) 2022 IAgrE. Published by Elsevier Ltd. All rights reserved.

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