Document Type

Thesis

Date of Degree Completion

Spring 2021

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Carey Gazis

Second Committee Member

Lisa Ely

Third Committee Member

Karl Lillquist

Abstract

The increase in global atmospheric CO2 over the last 200 years has generated an urgent need for strategies for sequestering carbon (C). Soil C, which has been depleted by land use change and agricultural practices, is a prime target for C storage. Land management practices, including no-till, cover cropping and crop rotation, and the application of C amendments such as compost and biochar, are suggested to increase C in the soil. Spoon Full Farm, near Thorp, WA, was a conventional hay farm until 2016, when management practices changed to implement some of these C sequestration strategies. A prior CWU M.S. thesis (Kautzman, 2019) characterized soil C and N and soil CO2 flux for each of the different fields on Spoon Full farm. Kautzman (2019) concluded that the application of compost to a vegetable garden increased soil C even beyond the C content of the compost and explored correlations between CO2 flux from the soil and different environmental parameters including temperature and soil moisture. The current study measured the C and N concentrations and isotope ratios at greater resolution with depth, in fields that had previously been surveyed. In addition, CO2 flux was monitored in two sections of a hay field; one section had received compost amendments while the other had not. Eight months after the compost amendment, the C content and CO2 fluxes in the two sections were statistically indistinguishable, indicating that the compost carbon had neither entered the soil nor impacted the microbial and root respiration rates. Additionally, compared to prior measurements, there was significant C loss in the previously composted vegetable garden, suggesting that increases in soil C from compost amendments are not permanent. Using the higher resolution C concentration measurements, CO2 flux measurements on composted and uncomposted fields in different seasons, and biomass measurements, a C budget was constructed for the farm. This C budget can be used to evaluate the impact of future land use changes on the farm. These results underscore the complexity and heterogeneity of these farm soils and invite future study as to the C dynamics on a spatial and temporal scale.

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