Less efficient residue-derived soil organic carbon formation under no-till irrigated corn

Authors: LEICHTY, SARAH - US Department Of Agriculture (USDA); COTRUFO, M - Colorado State University; Stewart, Catherine

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2020
Publication Date: 8/6/2020
Citation: Leichty, S., Cotrufo, M.F., Stewart, C.E. 2020. Less efficient residue-derived soil organic carbon formation under no-till irrigated corn. Soil Science Society of America Journal. 84(6):1928-1942. https://doi.org/10.1002/saj2.20136.
DOI: https://doi.org/10.1002/saj2.20136

Interpretive Summary: Conventional agricultural practices have decreased soil organic carbon (SOC) stocks, thus conservation agricultural practices have been proposed to rebuild SOC, increase soil health and mitigate greenhouse gas emissions. One conservation practice, no-till (NT), increases surface SOC concentrations compared to conventional tillage, but the gains are site-specific and could be vulnerable to loss over time. We measured residue C and soil C in CO2 discharge for one year after isotopically labeled grass residues were added to a NT, sprinkler-irrigated, continuous corn system near Fort Collins, CO. Cumulative residue respiration during the off season was highest for incorporated residue, but surface-applied residue was highest during the growing season and over the entire year. Surface-applied residue was vulnerable to C loss during the growing season suggesting reduced surface residue contribution to SOC compared to soil protected residue in the incorporated treatment. These results confirm that surface residue has a poor conversion to soil C under irrigation.

Technical Abstract: Conventional agricultural practices have decreased soil organic carbon (SOC) stocks, thus conservation agricultural practices have been proposed to rebuild SOC, increase soil health and mitigate greenhouse gas emissions. One conservation practice, no-till (NT), increases surface SOC concentrations compared to conventional tillage, but the gains are site-specific and could be vulnerable to loss over time. We mimicked agricultural residue management by altering the placement of isotopically (13C) labelled grass residues in a NT, sprinkler-irrigated, continuous corn system near Fort Collins, CO. Five treatments were implemented with either no residue or 13C-labelled residue applied to either the surface or incorporated into soils that were either disturbed (i.e., tilled) or undisturbed (i.e., NT). We measured residue C and soil C in CO2 efflux for one year from residue addition. Cumulative total respiration during the growing season was highest for surface-applied residue, but during the year was only higher than no-residue controls. Cumulative soil respiration did not differ across treatments for either season, indicating an absence of priming. Cumulative residue respiration during the off season was highest for incorporated residue, but surface-applied residue was highest during the growing season and year. Soil temperature explained over half of the variability in total and soil-derived CO2 fluxes, while a combination of residue moisture and soil temperature explained 36% of residue CO2 fluxes. Surface-applied residue was vulnerable to C loss during the growing season suggesting reduced surface residue contribution to SOC compared to incorporated residue that was protected within the soil matrix in this irrigated system.