Date of Graduation

12-2018

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

Kristofor R. Brye

Committee Member

Marty Matlock

Second Committee Member

Lisa S. Wood

Third Committee Member

David M. Miller

Keywords

Soil Carbon Dynamics, Soil Carbon Sequestration, Soil Carbon Storage

Abstract

The capture, conversion, and long-term storage of carbon dioxide (CO2) as soil organic carbon (SOC), a process known as soil C sequestration, is a possible solution to the current and ever-increasing threat of rising greenhouse gas emissions and global climate change. Tallgrass prairies, which once historically covered the country, are known to accumulate and sequester large amounts of C from the atmosphere deep within the soil, due to their extensive rooting systems. The purpose of this research was to increase understanding of soil C sequestration dynamics and general functioning in disappearing native grassland ecosystems within Arkansas, as well as the effects of physiographic region (Ozark Highlands and Grand Prairie Regions), soil moisture regime (udic and aquic), landuse (agriculturally managed and native undisturbed), and years under restoration on soil properties in native grassland ecosystems and other types of managed soils, in order to enhance soil rehabilitation and ecosystem restoration projects. Soil samples were collected from the top 10 cm in 2001/2002 or 2005 and again in 2016/2017 and the change over time was directly quantified for soil bulk density, pH, electrical conductivity, soil organic matter (SOM), total C (TC), total nitrogen (TN), and the fraction of TC and TN in SOM. Results indicate greater soil C sequestration occurring in the relatively cooler and drier climate of the Ozark Highlands compared to the Grand Prairie region. Despite the native prairie losing soil C at a rate of 4.7 Mg ha-1 yr-1 over the 15-year duration of the study, likely due to the effects of severe ecosystem fragmentation, soil C storage in 2016 was more than 2.5 times greater in the native prairie than in the cultivated agroecosystems in the Grand Prairie. Soil properties within the restoration study generally behaved as expected, with beneficial decreases in soil BD and increases in SOM, TC, TN, and TC and TN fractions of SOM occurring over time as restoration age increased and tended towards that in the native prairie. The soil C sequestration rate obtained for the restoration study through linear regression analysis was much lower (i.e. 0.0033 Mg C ha-1 yr-1) than the rate acquired through direct measurement over the 12-yr sampling period, which ranged from -0.21 to 0.12 Mg C ha-1 yr-1, implying that linear regression among soil C contents and ecosystem age can lead to potential substantial underestimations of soil C sequestration occurring in prairie restorations. This research demonstrates the value of direct measurements over time for assessing temporal changes in soil properties so that results can be used to guide expectations of the effects of physiographic region and soil moisture regime for future restoration activities to be as successful as possible.

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