Assessing the sensitivity and repeatability of permanganate oxidizable carbon as a soil health metric: An interlab comparison across soils


Jordon Wade, University of Illinois at Urbana-Champaign
Gabriel Maltais-Landry, University of Florida
Dawn E. Lucas, University of Florida
Giulia Bongiorno, Wageningen University
Timothy M. Bowles, University of California, Berkeley
Francisco J. Calderon, Central Great Plains Research Station
Steve W. Culman, The Ohio State University
Rachel Daughtridge, University of Illinois at Urbana-Champaign
Jessica G. Ernakovich, University of New Hampshire, DurhamFollow
Steven J. Fonte, Colorado State University
Dinh Giang, University of California Davis
Bethany L. Herman, The Ohio State University
Lindsey Guan, University of California, Berkeley
Julie D. Jastrow, Argonne National Laboratory
Bryan H. H. Loh, University of New Hampshire, Durham
Courtland Kelly, Colorado State University
Meredith E. Mann, The Ohio State University
Roser Matamala, Argonne National Laboratory
Elizabeth A. Miernicki, University of Illinois at Urbana-Champaign
Brandon Peterson, Central Great Plains Research Station
Mirjam M. Pulleman, Wageningen University
Kate M. Scow, University of California Davis
Sieglinde S. Snapp, Michigan State University
Vanessa Thomas, Michigan State University
Xinyi Tu, Michigan State University
Daoyuan Wang, University of California Davis
Nicolas A. Jelinski, University of Minnesota
Garrett C. Liles, California State University Chico
Felipe H. Barrios-Masias, University of Nevada
Devin A. Rippner, University of California Davis
Maria L. Silveira, University of Florida
Andrew J. Margenot, University of Illinois at Urbana-Champaign


Soil organic matter is central to the soil health framework. Therefore, reliable indicators of changes in soil organic matter are essential to inform land management decisions. Permanganate oxidizable carbon (POXC), an emerging soil health indicator, has shown promise for being sensitive to soil management. However, strict standardization is required for widespread implementation in research and commercial contexts. Here, we used 36 soils—three from each of the 12 USDA soil orders—to determine the effects of sieve size and soil mass of analysis on POXC results. Using replicated measurements across 12 labs in the US and the EU (n = 7951 samples), we quantified the relative importance of 1) variation between labs, 2) variation within labs, 3) effect soil mass, and 4) effect of soil sieve size on the repeatability of POXC. We found a wide range of overall variability in POXC values across labs (0.03 to 171.8%; mean = 13.4%), and much of this variability was attributable to within-lab variation (median = 6.5%) independently of soil mass or sieve size. Greater soil mass (2.5 g) decreased absolute POXC values by a mean of 177 mg kg−1 soil and decreased analytical variability by 6.5%. For soils with organic carbon (SOC) >10%, greater soil mass (2.5 g) resulted in more frequent POXC values above the limit of detection whereas the lower soil mass (0.75 g) resulted in POXC values below the limit of detection for SOC contents <5%. A finer sieve size increased absolute values of POXC by 124 mg kg−1 while decreasing the analytical variability by 1.8%. In general, soils with greater SOC contents had lower analytical variability. These results point to potential standardizations of the POXC protocol that can decrease the variability of the metric. We recommend that the POXC protocol be standardized to use 2.5 g for soils <10% SOC. Sieve size was a relatively small contributor to analytical variability and therefore we recommend that this decision be tailored to the study purpose. Tradeoffs associated with these standardizations can be mitigated, ultimately providing guidance on how to standardize POXC for routine analysis.


Soil Biogeochemistry and Microbial Ecology

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