Using Soil Testing Data to Monitor Changes in Maine Agricultural Soil Organic Carbon from 1995 to 2021

ABSTRACT

Estimates of soil organic matter (SOM) are commonly part of soil testing, and typically use the loss-on-ignition (LOI) method. To explore the utility of existing soil testing databases as a resource for estimating soil organic carbon (SOC) concentrations over time, we determined the relationship between SOM estimated by LOI and SOC measured using IR detection of CO₂ for Maine soils. We then examined trends in SOC concentrations in Maine agricultural soils over the past 27 years using data from 97,713 standard soil samples received by the Maine Soil Testing Service. For 91 agricultural soil samples representative of Maine cropping systems, we found that the standard LOI temperature used by the Maine Soil Testing Service, 375°C, produced LOI values that correlated more strongly with SOC measured by IR detection of CO₂ than the three higher temperatures we studied, although all temperatures produced data that was well correlated (R² values from 0.95 to 0.98). Soil texture did not influence the correlation. Our analysis of soil testing data from 1995 to 2021 suggested increases in SOC concentrations in soils planted to grain and hay, and possibly corn, broadly corresponding with changing agricultural practices occurring over this time frame. Of our four focal crop categories, only potato soils decreased in SOC concentration from 1995 to 2021, underscoring the unique challenges associated with potato soil management relative to other cropping systems in Maine. Our study confirms the potential utility of soil testing databases in assessing changes in SOC concentrations in agricultural soils over decades.

KEYWORDS:

• Carbon sequestration
• loss on ignition
• soil organic carbon
• soil organic matter
• soil testing

Acknowledgements

We appreciate the assistance and insights of Bruce Hoskins of the Maine Soil Testing Service and his willingness to share his vast knowledge of soil testing. This project was supported by USDA-NIFA-2018-67019-27801 and the Maine Agricultural and Forest Experiment Station (MAFES) Hatch Project ME-02163.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data will be made available on request.

Additional information

Funding

The work was supported by the Maine Agricultural and Forest Experiment Station [Hatch Project ME-02163]; National Institute of Food and Agriculture [USDA-NIFA-2018-67019-27801].