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Colorado State University (2021)

Roles of residue management, microbes and aggregation in soil carbon stabilization under semiarid, irrigated corn

Oleszak, Hanna

Titre : Roles of residue management, microbes and aggregation in soil carbon stabilization under semiarid, irrigated corn

Auteur : Oleszak, Hanna

Université de soutenance : Colorado State University

Grade : Master of Science (MS) 2021

Résumé partiel
With atmospheric carbon dioxide levels continuously on the rise, it is critical that we focus our efforts on sequestering carbon (C) to slow global warming. To maximize these efforts, it is furthermore important to understand the pathways by which plant C inputs form soil organic carbon (SOC), as these pathways may inform the efficiency and duration of C stabilization. No-tillage is often recommended as a universal tool to draw C into the soil, yet literature reports mixed effects of tillage practices on C accrual. To maximize our efforts and best recommend agricultural practices for C sequestration, it is important to understand how the incorporation of residue within the mineral soil and disturbance associated with tillage impact plant residue C dynamics, as mediated by changes in microbial community and soil structure. While microbes play the active role in decomposing organic matter, soil structure can act as a gatekeeper to microbial accessibility to organic matter ; thus, the effects of disturbance and residue incorporation upon the interplay of these two variables is highly important to consider. We used 13C labeled plant residue to track the movement of residue C in incorporated vs. surface-applied residue treatments in irrigated, semiarid corn for a period of 30 months. Both carbon dioxide (CO2) fluxes and soil cores were tested for total C and 13C enrichment to quantify residue-derived C contribution to CO2 efflux and to C accrual in the mineral soil over time, respectively. Furthermore, aggregate size fractionation and microbial community (via phospholipid fatty acids, PLFAs) were analyzed to assess how residue placement location and disturbance affect the mechanisms behind residue decomposition, and ultimately soil C stabilization. The incorporation of residue in the mineral soil resulted in significantly greater SOC formation efficiencies and greater SOC accrual in the first year, compared to the surface-application of residue. However, differences in SOC accrual subsided after 30 months, even though higher CO2 losses were measured in the surface applied residue treatments after 30 months. Residue-derived microbial biomass was greater in INC than SA or SA-NR at all timepoints, although this was only significant at 6 and 12 months. Residue-derived microbial community composition differed between early and later stages of decomposition, as well as between disturbed and undisturbed treatments.

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