Comparison of two alkali trap methods for measuring the flush of CO2

Authors: Franzluebbers, Alan; Veum, Kristen

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2019
Publication Date: 4/24/2020
Citation: Franzluebbers, A.J., Veum, K.S. 2020. Comparison of two alkali trap methods for measuring the flush of CO2. Agronomy Journal. 112:1279-1286. https://doi.org/10.1002/agj2.20141.
DOI: https://doi.org/10.1002/agj2.20141

Interpretive Summary: Soil health is an important concept that has gained strong traction within the farming community. Biological indicators of soil health are the most controversial due to a variety of approaches being used without sufficient calibration. Scientists from the USDA Agricultural Research Service in Raleigh NC and Columbia MO collaborated on a project to evaluate two different soil biological activity protocols. Soils from two long-term field experiments comparing a wide range of management conditions in Missouri and North Carolina were tested. Both biological activity protocols gave results that were highly related across a large gradient, but results differed in obvious ways based on differences in specific steps. Although quick soil-test methods are desirable, they still need to adhere to basic principles of analysis. We showed that alternative methods to estimate soil biological activity need to give due attention to temperature and water conditions during incubation. Unnecessary variations or spurious results could otherwise be produced, which are problematic in making interpretations for farmers. Soil-test biological activity is an important attribute of soil health, and although a variety of methods could be possible, some standardization is needed for sound evaluations.

Technical Abstract: Soil biological activity is a key feature of healthy soil. The flush of CO2 during the first few days after rewetting of a dried soil has been used as a rapid indicator of soil biological activity, but a variety of approaches have emerged without sufficient calibration among methods. We assessed two alkali trap methods that used different soil weight, water delivery approach, and incubation length and temperature for determining the flush of CO2 from two long-term field experiments in Missouri (silt loam soils) and North Carolina (sandy loam and loamy sand soils). The research method relied on standard temperature and moisture conditions, while the commercial method had deviations from these standards. The two methods were highly related to each other (r2 = 0.93 for Missouri soils and r2 = 0.68 for North Carolina soils), but results differed in absolute value. Both methods were able to discern strong depth stratification of soil biological activity, as well as crop management treatment effects. However, subtle differences in soil biological activity due to landscape position and soil texture were significant only with the research method. Standardized soil water content and incubation temperature are critical for all soil biological activity methods. We suggest that greater standardization of commercial soil testing protocols be developed in accordance with verified research approaches to increase reliability and value to stakeholders.