Soil organic carbon predictions in Subarctic Greenland by visible–near infrared spectroscopy

ABSTRACT

Release of carbon from high-latitude soils to the atmosphere may have significant effects on Earth’s climate. In this contribution, we evaluate visible–near-infrared spectroscopy (vis-NIRS) as a time- and cost-efficient tool for assessing soil organic carbon (SOC) concentrations in South Greenland. Soil samples were collected at two sites and analyzed with vis-NIRS. We used partial least square regression (PLS-R) modeling to predict SOC from vis-NIRS spectra referenced against in situ dry combustion measurements. The ability of our approach was validated in three setups: (1) calibration and validation data sets from the same location, (2) calibration and validation data sets from different locations, and (3) the same setup as in (2) with the calibration model enlarged with few samples from the opposite target area. Vis-NIRS predictions were successful in setup 1 (R² = 0.95, root mean square error of prediction [RMSEP] = 1.80 percent and R² = 0.82, RMSEP = 0.64 percent). Predictions in setup 2 had higher errors (R² = 0.90, RMSEP = 7.13 percent and R² = 0.78, RMSEP = 2.82 percent). In setup 3, the results were again improved (R² = 0.95, RMSEP = 2.03 percent and R² = 0.77, RMSEP = 2.14 percent). We conclude that vis-NIRS can obtain good results predicting SOC concentrations across two subarctic ecosystems, when the calibration models are augmented with few samples from the target site. Future efforts should be made toward determination of SOC stocks to constrain soil–atmosphere carbon exchange.

KEYWORDS:

• Soil organic carbon
• visible–near-infrared spectroscopy
• subarctic
• Greenland

Supplemental data

Supplemental data for this article can be accessed on the publisher’s website.

Acknowledgments

The authors thank Lasantha Herath, Cecilie Hermanssen, Rene Larsen, Trine Nørgaard, and Stig Rasmussen for assistance in the field; Hans Kapel and Adala Lund for logistical support; the Greenlandic Agricultural Consulting Service (Nunalerinermik Siunnersorteqarfik) in Qaqortoq and Upernaviarsuk for access to the land and their equipment; Bjarne Holm Jakobsen for providing background soil data and insightful discussions for this study; and Bente Rasmussen for laboratory assistance. Finally, the authors would like to thank Jacob Yde and other anonymous reviewers for their constructive comments which improved the paper.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was partly funded by a research grant (AUFF-E-2016-9-36) from the Aarhus University Forskningsfond and the research project “Glacial Flour as New, Climate-Positive Technology for Sustainable Agriculture in Greenland: NewLand,” funded by the Independent Research Fund Denmark.