Assessing the Potential of Pinyon-Juniper-Derived Biochar to Sequester Carbon in Two Nevada Soils and Climates
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Authors
Duggan, Kevin Wayne
Issue Date
2022
Type
Thesis
Language
Keywords
Biochar , Carbon 13 , Carbon sequestration , Efflux , Particle size , Pinyon-Juniper
Alternative Title
Abstract
Soil carbon (C) plays a vital role in the global C cycle by acting as a reservoir for long-term C storage. Biochar is a form of black C that is highly recalcitrant lending it the ability to potentially store C in soil for millenia that would otherwise likely be released back into the atmosphere much sooner. In addition, biochar has also been touted as a means to improve soil quality by enhancing water and nutrient retention due to an increased surface area and associated cation exchange capacity. These properties make biochar a potential amendment for urban forestry soils, especially under environmental conditions not ideal for tree growth, such as the arid regions in the US where soils can be low in fertility.In this study, biochar was assessed for its potential to sequester C in two different Nevada soils, a Mollisol located near Reno and and an Entisol close to Las Vegas, respectively. The biochar was derived from Pinyon Pine and Juniper trees from eastern Nevada woodlands using portable metal kilns.
To assess the C sequestration potential of the biochar, a combination of field and laboratory experiments were conducted. In my field study, I used four different treatments; 1) trees with biochar; 2) trees without biochar, 3) no trees with biochar, and 4) no trees without biochar. The tree spcies ued was the Lacebark Elm (Ulmus parvifolia) which is common in urban environments. To analyze biochar degradation, litterbags were filled with biochar and incubated with the trees at different depths. After 3 and seventeen months, a subset of the litterbags were retrieved, and total mass, C, and nitrogen (N) were measured. A subset of litterbags was treated with formaldehyde in an attempt to minimize biotic degradation so abiotic factors would dominate. Soil CO2 efflux was measured on all soil plot treatments to assess soil (microbial and root) respiration. Finally, soil core samples were taken out of each plot treatment and measured for changes in content of total carbon (%TC) and nitrogen (%TN) after 17 months.
In the laboratory incubation, biochar with different particle sizes were incubated for 90 days with and without soil. Both respiration rate and 13C were measured after 24 hours of incubation for each sampling point to analyze biochar degradation. The litterbag study showed mass loss in both the formaldehyde-treated (higher -6.7%) and untreated biochar (-2.1%) with Washoe Valley having a similar result. The %TC and %TN litterbag results showed an increase of %TN in Washoe Valley (23%) and a decrease in %TC in Las Vegas (14%). Soil CO2 efflux measurements showed biochar’s ability to stimulate soil respiration rates with or without trees compared to the untreated plots. Soil %TC in Las Vegas decreased over time, but remained constant in Washoe Valley. Biochar had no significant impact on %TN over time in either soil. Laboratory incubations showed that the influence of particle size on the impact of biochar on C sequestration depended on temperature and 13C analysis demonstrated that the biochar is consumed by microbial communities. Both field and and laboratory studies demonstrated that PJ biochar is recalcitrant even under conditions optimal for decomposition.