Soil organic matter (SOM) is a critical biogeochemical pool that can be managed as part of global efforts to conserve nutrients and enhance carbon (C) sequestration. But reliably increasing SOM has proven difficult because most of the organic matter that enters soil as plant litter and organic amendments (i.e., compost, manure) is susceptible to decomposition by soil microorganisms and eventually is lost to the environment as greenhouse gases and non-point source pollution. Many soils lack the physical and/or chemical properties that enable some human-modified soils (e.g., terra preta soils in the Amazon Basin) to stabilize and retain C and nutrients in SOM while maintaining relatively high levels of productivity compared to surrounding natural soils that formed under similar conditions. I hypothesized that two of the major stabilizers of organic matter common to terra preta soils of the Amazon basin – black carbon (biochar) and poorly crystalline, reactive iron (Fe) minerals – could be applied to a fine-textured soil from Southwest Virginia to improve the accumulation and retention of C and nitrogen (N). I used a field experiment to compare the effects of three types of locally-produced biochars applied with and without an organic N fertilizer (blood meal) on soil C and N availability. I then used an incubation experiment featuring the soils from the aforementioned field experiment to examine the effects of applying Fe2+ -treated manure effluent on the retention of C and N in unamended and hardwood biochar-amended soils. I found that biochar adsorbed inorganic N in all cases, while providing a reliable, stable increase in SOM due to its recalcitrant nature. However, the manure effluent used in the incubation experiment stimulated the decomposition of mineral-associated organic matter (MAOM), with the addition of Fe2+ to the manure mitigating this apparent positive priming effect and the presence of biochar actually reversing this effect and promoting an increase in MAOM following manure application to biochar-amended soil. Overall, biochar stimulated the retention of N by decreasing the leachable inorganic N in the soil and enhanced soil C stocks. Additionally, biochar applications had the added benefit of promoting the accumulation of manure in soil as stable, microbially-processed MAOM, while co-applying Fe2+ with manure only served to inhibit the priming of native soil C. / Master of Science / Organic matter is an important constituent of all soils. Farmers and gardeners would like to increase the organic matter on their lands to improve their crop yields and health of their soils, yet people in many regions of the world struggle with actually getting long-lasting forms of organic matter to accumulate in soils. Moreover, managing soils to increase the amount of carbon stored in these long-lasting forms has the benefit of offsetting human contributions to atmospheric carbon dioxide and global warming. Some soils stabilize and build up organic matter more efficiently than others, and I hypothesized that if two well-known soil materials that help to stabilize organic matter – charcoal and iron – were added to a soil, then the accumulation of organic matter in the soil could be improved. The first part of my research was a field experiment in which three different kinds of charcoal were added either with or without an organic fertilizer to the soil in a Southwest Virginia pasture. I then measured the amount of carbon in the soil and determined that charcoal additions increased soil carbon and helped to retain mobile forms of plant nutrients. The second part of my research used the charcoal-treated and untreated soils from the field experiment for a project where cow manure was co-applied with three levels of iron and added to soils in jars in a controlled laboratory setting. The jars were then maintained at an ideal moisture and temperature for the growth of microbes for 70 days and analyzed afterwards. I found that the manure caused the organic matter in the soil to be consumed by microbes, while charcoal caused the organic matter from the manure to accumulate and remain. Adding iron with the manure prevented the microbes from consuming the pre-existing organic matter in the soil, but did not contribute to the retention of the manure in the soil. Overall, while both iron and charcoal influenced the retention of organic matter in soil, biochar proved to be more effective at stabilizing manure organic matter than the iron additions.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/110436 |
| Date | 02 June 2022 |
| Creators | Conner, Jared P. |
| Contributors | Biological Sciences, Barrett, John E., Hotchkiss, Erin R., Strahm, Brian D. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | Creative Commons Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
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