Whole-profile soil organic matter content, composition, and stability under cropping systems that differ in belowground inputs

Authors: POFFENBARGER, HANNA - University Of Kentucky; Olk, Daniel - Dan; Cambardella, Cynthia; KERSEY, JORDAN - Iowa State University; LIEBMANN, MATTHEW - Iowa State University; MALLARINO, ANTONIO - Iowa State University; SIX, JOHAN - Swiss Federal Institute Of Technology Zurich; CASTELLANO, MICHAEL - Iowa State University

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2019
Publication Date: 4/1/2020
Citation: Poffenbarger, H.J., Olk, D.C., Cambardella, C.A., Kersey, J., Liebmann, M., Mallarino, A., Six, J., Castellano, M.J. 2020. Whole-profile soil organic matter content, composition, and stability under cropping systems that differ in belowground inputs. Agriculture, Ecosystems and Environment. 291. https://doi.org/10.1016/j.agee.2019.106810.
DOI: https://doi.org/10.1016/j.agee.2019.106810

Interpretive Summary: Soil carbon plays important roles in soil performance and water quality. Its effectiveness is partially controlled by its quantity in soil. The amounts of carbon stored at greater soil depths are less than the potential amounts that could be stored there. We studied whether crops with deeper roots could increase the soil carbon storage at depth. We found that crops with deeper roots did not contribute consistently to carbon storage at depth. These results indicate that crop selection is often not a practical tool for increasing soil carbon at depth, and other management tools should be investigated. These results are useful for soil scientists, ecologists, and land managers.

Technical Abstract: Subsoils have been identified as a potential sink for carbon dioxide, due to the capacity or large stocks of soil organic carbon (SOC) but low actual SOC concentrations. One proposed strategy to increase subsoil C stocks is to enhance C inputs to the subsoil by integrating deep-rooted perennial crops into crop rotations. Using three long-term field trials in Iowa (study durations of 60, 35, and 12 years), we examined the effects of crop rotation [maize (Zea mays L.)-soybean (Glycine max (L.) Merr)-oat (Avena sativa L.)/alfalfa (Medicago sativa L.)-alfalfa or maize-maize-oat/alfalfa-alfalfa vs. maize-soybean rotation) on above- and below-ground C inputs as well as SOC content, biochemical composition, and distribution among physical fractions at different depths throughout the soil profile. Average annual C inputs were similar for both rotations, but the proportion of C delivered below ground was 20-35% greater in the 4-yr rotations. Despite the long duration of these studies, the effect of crop rotation on SOC content to 90 cm was inconsistent across sites, ranging from -7% to +17% in the 4-yr rotation relative to the 2-yr rotation. Moreover, at the one site where SOC was greater in the crop rotation with more belowground inputs, the effect of crop rotation on SOC content was distributed across the full profile rather than limited to the subsoil depth increments (i.e., below 30 cm). Crop rotation had minimal effects on the enrichment of microbial biomarkers, C-normalized lignin concentration, and the proportions of SOC as free particulate organic matter (POM), microaggregate-occluded POM, easily-dispersed silt plus clay, and microaggregate-derived silt plus clay. We conclude that adoption of crop rotations with enhanced belowground C inputs may increase total profile SOC but has minor impact on the vertical distribution, biochemical composition, or stability of organic C in Mollisols of the Midwest U.S.