What does it take to detect a change in soil carbon stock? A regional comparison of minimum detectable difference and experiment duration in the north central United States

Abstract

Variability in soil organic carbon (SOC) results from natural and human processes interacting across time and space, and leads to large variation in the minimum difference in SOC that can be detected with a particular experimental design. Here we report a unique comparison of minimum detectable differences (MDDs) in SOC, and the estimated times required to observe those MDDs across the north central United States, calculated for the two most common SOC experiments: (1) a comparison between two treatments, e.g., moldboard plow (MP) and no-tillage (NT), using a randomized complete block design experiment; and (2) a comparison of changes in SOC over time for a particular treatment, e.g., NT, using a randomized complete block design experiment with time as an additional factor. We estimated the duration of the two experiment types required to achieve MDD through simulation of SOC dynamics. Data for the study came from 13 experimental sites located in Iowa, Illinois, Ohio, Michigan, Wisconsin, Missouri, and Minnesota. Soil organic carbon, bulk density, and texture were measured at four soil depths. Minimum detectable differences were calculated with probability of Type I error of 0.05 and probability of Type II error of 0.15.The MDDs in SOC were highly variable across the region and increased with soil depth. At 0 to 10 cm (0 to 3.9 in) soil depth, MDDs with five replications ranged from 1.04 g C kg -1 (0.017 oz C lb ; 3%) to 3.12 g C kg -1 (0.050 oz C lb -1 ; 13%) for SOC change over time. Large differences were also predicted in the experiment duration required to detect a difference in SOC between MP and NT (from 8 to >100 years with five replications), or a change in SOC over time under NT management (from 11 to 71 years with five replications). At most locations, the time required to detect a change in SOC under NT was shorter than the time required to detect a difference between MP and NT. Minimum detectable difference and experiment duration decreased with the number of replications and were correlated with SOC variability and soil texture of the experimental sites, i.e., they tended to be lower in fine textured soils. Experiment duration was also reduced by increased crop productivity and the amount of residue left on the soil. The relationships and methods described here enable the design of experiments with high power of detecting differences and changes in SOC and enhance our understanding of how management practices influence SOC storage.

Six years of different tillage systems affected aggregate-associated SOM in a semi-arid loam soil from Central Iran

“…Our results suggest that CT combined with residue addition may not adversely affect bulk SOM contents and that SOM was not responsive to tillage practices during the six years of tillage treatments when residue additions were similar under tillage systems. Lack of a positive effect of RT practices on SOM in short-term experiments is common in different soils and was also observed in other studies under different climatic conditions across different ecosystems (Shirani et al, 2002;Grandy and Robertson, 2006;Green et al, 2007;Jin et al, 2009;Paul et al, 2013), and thus a long-term practice of conservation tillage might be needed for a large accumulation of SOM (Hunt et al, 1996;Plaza-Bonilla et al, 2014;Necpálová et al, 2014). Conservation tillage practices do not always increase SOM content (Liebig et al, 2004) and the consequences of tillage systems are commonly site-specific and vary from an increased SOM only in the top few cm (Liebig et al, 2004;Mijangos and Garbisu, 2010) to little (Geisseler and Horwath, 2009;Heinze et al, 2010) or no effect (Grandy and Robertson, 2006;Paul et al, 2013;Plaza-Bonilla et al, 2014) under both RT and MT systems.…”

Measuring Rotation and Manure Effects in an Iowa Farm Soil Health Assessment

“…Different sampling schemes and data interpretation criteria are needed as scale increases from intra-row to watershed assessment (e.g., Collado and Karlen, 1992;Grigera et al, 2007;Tomer et al, 2006). Field variability versus management-induced soil property changes can be difficult to detect (Beehler et al, 2017;Cambardella et al, 1994;Hammac et al, 2016;Necpálová et al, 2014). Tillage practices, including earthworm activity, and associated equipment traffic patterns can increase spatial heterogeneity (Grigera et al, 2007;Kaspar and Parkin, 2011;Kaspar et al, 2001;Williams et al, 2016Williams et al, , 2017.…”

How does tillage intensity affect soil organic carbon? A systematic review

“…One review was identified through screening of search results from the search update [40]. The bibliography of this review article was screened for potentially relevant articles that may have been missed by the searches.…”