Which Soil Carbon Fraction is the Best for Assessing Management Differences? A Statistical Power Perspective

Abstract

Active fractions of soil C such as particulate organic C (POC) and short‐term mineralizable C (SMC) respond faster than total organic C (TOC) to management induced changes in soil C. However, the active fractions of organic C can possibly have larger variability that decreases the detectability of management effects on soil C. The objectives of this study were to (i) assess the relative usefulness of TOC, POC, and SMC as criteria of management induced changes on soil C and (ii) investigate if using auxiliary soil and topographical information can aid in increasing the usefulness of these criteria in studies conducted across large spatial scales. Data were collected at locations with two contrasting topographical positions (slope and depression) within 10 agricultural fields in conventional and cover crop based row crop managements at the 0‐ to 20‐, 35‐ to 50‐, and 70‐ to 90‐cm depths. The results showed that to detect differences between the management systems with an acceptable type II error of 0.20, an 80% difference in TOC and a 50% difference in SMC were needed. The statistical power for POC was never in an acceptable range. The use of auxiliary soil and topography information via analysis of covariance decreased the sizes of the minimal detectable differences. Given the faster reaction to management of SMC as compared with TOC, and its lower variability as compared with POC, we recommend SMC as the preferred C fraction for detecting treatment induced differences in organic C stocks in agricultural field experiments, especially in deeper soil layers.

Scaling-up: cover crops differentially influence soil carbon in agricultural fields with diverse topography

“…For both sets of data analysis we added percentage of sand and terrain slope as covariates to the statistical models and kept covariates in the model if their contribution was statistically significant at p <0.1 level. The details of the analysis of covariance are described in Ladoni et al (2015).…”

“…Sand content was measured for all of the samples as a part of POC measurement. Soil bulk density and particle size distributions for 10 of the studied fields were available from a previous study (Ladoni et al, 2015). Soil bulk density of the undisturbed soil was measured as instructed by Hao et al (2008).…”

“…Both POM and SMC were demonstrated to be closely related to several labile pools of organic C and to be sensitive to management changes (Cambardella and Elliott 1992;Collins et al, 2000;Chan, 2001;Haynes, 2005;Franzluebbers et al, 2000;Culman et al, 2013;Ladoni et al, 2015).…”

Comparison of Permanganate‐Oxidizable Carbon and Mineralizable Carbon for Assessment of Organic Matter Stabilization and Mineralization

“…Short-term mineralizable C, on the other hand, correlates well with longterm C mineralization rates, soil microbial biomass, particulate organic matter, and nutrient mineralization (Franzluebbers et al, 2000a;Haney et al, 2001Haney et al, , 2008. Carbon mineralization also has been shown to be sensitive and an early indicator of management-induced changes in total soil C (Franzluebbers and Stuedemann, 2008;Franzluebbers et al, 2000a;Haney et al, 2001;Ladoni et al, 2015;Schomberg et al, 2009;Vahdat et al, 2010). There have been a limited number of studies that examined the relationship between POXC and short-term mineralizable C (Culman et al, 2013;Morrow et al, 2016;Wang et al, 2003), but, to our knowledge, there has been no comprehensive evaluation across a wide range of soil types, management histories, and geographic locations.…”

“…Thus, rather than testing for total SOM, as is often the case in standardized soil testing, testing the active organic matter pool provides better insight into how changes in management affect nutrient cycling and potential soil C accumulation or loss (Haynes, 2005;Lewis et al, 2011;Wander, 2004;Wardle, 1992). For example, accumulation of particulate organic matter is considered to represent an initial stage of C sequestration in soils and, as a consequence, is widely used in research settings (Awale et al, 2013;Haynes, 2005;Ladoni et al, 2015;Mirsky et al, 2008). However, most analytical methods for measuring the active SOM pool are time consuming and expensive, limiting their full use as routine tests for farmers (Franzluebbers, 2016).…”