Date of Award

Fall 12-31-2021

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Forest Resources

Advisor

Ivan J. Fernandez

Second Committee Member

Katherine Crowley

Third Committee Member

Shawn Fraver

Additional Committee Members

Daniel Hayes

Aaron Weiskittel

Abstract

Soil organic carbon (SOC), as one of the largest C pools in terrestrial ecosystems, plays a key role in governing soil ecosystem processes and climate regulation. Climate change concerns have resulted in a rapidly growing interest in understanding the potential for natural climate solutions (NCS) that include enhancing SOC sequestration and reduce net atmospheric greenhouse gas (GHG) emissions. This research focused on addressing information needs about SOC in Maine, specifically in evaluating available soil databases to accurately quantify SOC density and concentration, and study the response of selected representative Maine soils to biochar amendments under a changing climate.

Maine SOC was estimated from three different but complementary databases that included the Forest Inventory and Analysis (FIA), the Soil Survey Geographic Database (SSURGO), and the Rapid Carbon Assessment (RaCA) databases. We analyzed and compared data from these sources to estimate SOC stock in Maine under various land uses and also explored the relationships between soil properties and SOC retention. Estimates of SOC densities, particularly at shallow depth, varied significantly among databases, reflecting the differences in program design and sampling protocols for each database. Significant correlations between SOC and soil texture and soil drainage highlighted the dominance of silt and clay fractions in C retention in Maine soils.

The scientific literature has demonstrated the potential C benefits of amending soils with biochar as an NCS. Here, we report results from a series of incubation experiments and modeling simulations evaluating the influences of biochar additions. Empirical incubations showed that biochar amendments significantly increased SOC, but had no significant effect on soil respiration, highlighting the potential for biochar to enhance C sequestration. The potential C benefits of biochar amendments to increase SOC were further supported by numerical modeling. Modeling also indicated that although future climate warming would have negative consequences for SOC sequestration, the net effects of climate were relatively small compared to the C benefits of biochar soil amendments. In addition, biochar amendments improved some soil health properties including pH, extractable cations, and water holding capacity. However, plant response to soil biochar amendments in the bioassay study was inconsistent.

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