An evaluation of carbon indicators of soil health in long-term agricultural experiments

Authors: LIPTZIN, DANIEL - Soil Health Institute; NORRIS, CHARLOTTE - Soil Health Institute; CAPPELLAZZI, SHANNON - Soil Health Institute; BEAN, G - Soil Health Institute; COPE, MICHAEL - Soil Health Institute; GREUB, KELSEY - Soil Health Institute; RIEKE, ELIZABETH - Soil Health Institute; TRACY, PAUL - Soil Health Institute; ABERLE, EZRA - North Dakota State University; Ashworth, Amanda; Baumhardt, Roland - Louis; Dell, Curtis; Derner, Justin; Ducey, Thomas; Novak, Jeffrey; Dungan, Robert - Rob; Fortuna, Ann Marie; Kautz, Mark; Kitchen, Newell; Leytem, April; Liebig, Mark; Moore, Philip; Osborne, Shannon; Owens, Phillip; Sainju, Upendra; Sherrod, Lucretia; Watts, Dexter

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2022
Publication Date: 6/15/2022
Citation: Liptzin, D., Norris, C.E., Cappellazzi, S.B., Bean, G.M., Cope, M., Greub, K.L., Rieke, E.L., Tracy, P.W., Aberle, E., Ashworth, A.J., Baumhardt, R.L., Dell, C.J., Derner, J.D., Ducey, T.F., Novak, J.M., Dungan, R.S., Fortuna, A., Kautz, M.A., Kitchen, N.R., Leytem, A.B., Liebig, M.A., Moore Jr., P.A., Osborne, S.L., Owens, P.R., Sainju, U.M., Sherrod, L.A., Watts, D.B. 2022. An evaluation of carbon indicators of soil health in long-term agricultural experiments. Soil Biology and Biochemistry. 172. Article 108708. https://doi.org/10.1016/j.soilbio.2022.108708.
DOI: https://doi.org/10.1016/j.soilbio.2022.108708

Interpretive Summary: Soil health is gaining global attention as have practices that improve soil quality. A variety of terms (e.g. soil tilth, quality, etc.) and conditions have been used over the last century to describe a soil's health, however, a central focus of all of them is a soils carbon stocks. Although, little is known about the different forms of soil carbon and how they are changed by various best management practices (crop rotations, cover crop, organic inputs, rotational grazing, type and timing of tillage, and irrigation), as well as by conditions that cannot be controlled such as a soil's inherent properties (clay, silt, sand) and local climatic conditions (precipitation and temperature). Researchers therefore set out to evaluate soil carbon indicators in long-term experiments throughout North America in order to examine the continental-scale drivers of soil carbon and the effects of soil health practices on carbon. This study found that, throughout North America, carbon indicators were all greater at sites with lower-temperatures, increased precipitation, and soils with greater clay content. Forms of soil carbon were greater under decreased tillage, cover crops, organic amendments (e.g. animal manures), and residue retention, but not under greater crop rotations. Overall, these results provide insight into how management and environmental conditions drive soil carbon for helping combat climate change and improve a soil's capacity to cycle nutrients and improve food production.

Technical Abstract: Soil organic carbon (SOC) is integral to soil health. However, there are other indicators (e.g. potential C mineralization, permanganate oxidizable C, water extractable organic C and 'beta-glucosidase enzyme activity) may provide additional information about C dynamics and microbial activity. We used a subset of indicators from the North American Project to Evaluate Soil Health Measurements to examine the continental scale drivers of these indicators, the relationships among the indicators, and the effects of soil health practices on the indicators. All the indicators had greater values at lower temperatures, and most were greater with increased precipitation and greater clay content. The indicators were strongly correlated across sites, with the strongest relationship between SOC and permanganate oxidizable C. The indicators responded to decreasing tillage, inclusion of cover crops in a rotation, application of organic nutrients, and retention of residue, but not the number of crops in a rotation. The effect of decreased tillage on the C indicators was generally greater at sites with higher precipitation. The magnitude and direction of the management response was generally consistent within a site for all the indicators. The indicators other than SOC all have methodological issues that can hinder a universal interpretation of their magnitude. However, given that the indicators generally respond in similar ways to inherent site characteristics and management, they all could be used as soil health indicators. Balancing the cost, sensitivity, interpretability, and availability at the commercial labs, a 24hr potential C mineralization assay could provide the most benefit to measure in conjunction with SOC, but measuring multiple indicators can provide additional confidence about C dynamics.