Comparing Four Methods of Measuring Soil Organic Matter in North Carolina Soils

Abstract

Results of agronomic management effects on SOM are inconsistent among methods. Correlations among methods of measuring SOM differ depending on soil. Soil organic matter content should be compared using similar procedures. Soil organic matter (SOM) provides many beneficial soil ecosystem services for sustainable soil management, but it is unclear how results from different methods of measuring SOM should be compared when making soil management decisions. To compare different methods, we used 84 soil samples from long‐term agronomic trials in the coastal plain, piedmont, and mountain regions of North Carolina. Coastal plain and mountain trials included combinations of tillage and management (conventional vs. organic), whereas piedmont trials were configured to evaluate tillage intensity. The methods used to measure SOM were Walkley‐Black (WB), mass loss on ignition (LOI), automated dry combustion (ADC), and humic matter (HM) colorimetry. Correlations among LOI, WB, and ADC were significant (p < 0.0001) for SOM measured from the total population of soils, but variability due to location implied that HM had no correlation to other methods. For measures of soil organic carbon compared to SOM, the WB results were biased high compared to ADC, and ADC was more strongly correlated to LOI than WB. When using the methods to evaluate the effects of agronomic management on SOM, results varied for different methods and locations. Conservation management did not consistently accumulate more SOM than other soil management practices, and no method consistently differentiated soils based on management. Variation in the composition of SOM measured using conventional methods may be causing discrepancies in reported changes in SOM content over time. To avoid confusion about how agronomic management affects SOM, assessments should limit comparisons to methodologies with similar measurement protocols.

Metagenomic insights into the bacterial community structure and functional potentials in the rhizosphere soil of maize plants

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The Response of Soil Nutrients and Microbial Community Structures in Long-Term Tea Plantations and Diverse Agroforestry Intercropping Systems

“…The hydrochloric acid and flame photometry analyzed the AP and AK, respectively [37]. SOM was measured using the oxidative thermal potassium dichromate oxidation method [38].…”

Optimization of carbon stock models to local conditions using farmers' soil tests: A case study with AMGv2 for a cereal plain in central France

“…, 1991; Soon & Abboud, 1991), the quantification of organic C depends on testing methods (Roper et al. , 2019). Therefore, the most consistent results are obtained by testing all the samples by one method in a single laboratory at the same time (Dimassi et al.…”

“…To obtain a reliable measure of organic C, inorganic C should be removed by acid treatment prior to combustion (Meersmans et al, 2009), or at least determined separately to allow a correction for it. Although strong correlations between the different methods have been demonstrated for different soil types (Grewal et al, 1991;Soon & Abboud, 1991), the quantification of organic C depends on testing methods (Roper et al, 2019). Therefore, the most consistent results are obtained by testing all the samples by one method in a single laboratory at the same time (Dimassi et al, 2014;Autret et al, 2016).…”