Date of Graduation

12-2014

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Brye, Kristofor R.

Committee Member

Savin, Mary C.

Second Committee Member

Gbur, Edward E. Jr.

Third Committee Member

Mason, Richard E.

Keywords

Bioenergy; Cottonwood; Soil Carbon; Soil Respiration; Soil Science; Switchgrass

Abstract

Marginal land of the Lower Mississippi Alluvial Valley (LMAV) has the potential to be utilized for the production of bioenergy feedstocks. Soil respiration is the gaseous emission of carbon dioxide (CO2) from microbes and plant roots in the soil, and these emissions play an important role in the global cycling of carbon. Soil respiration can act as a positive feedback affecting climate change, and has been shown to vary depending on soil moisture, temperature, and vegetation. The objectives of this study where to evaluate the effects of land use [switchgrass (Panicum virgatum), cottonwood (Populus deltoides), and a soybean (Glycine max)-grain sorghum (Sorghum bicolor) agroecosystem] on monthly soil respiration and estimated annual CO 2 emissions on a silt loam in east-central Arkansas throughout 2012 and 2013. Annual CO 2 emissions were calculated by linear interpolation between monthly measurements. Soil respiration from all three ecosystems followed the same general trend: increasing from January to May and decreasing from September to December, peak fluxes differed significantly (p < 0.05) among ecosystems for both years. Peak fluxes in 2012 were achieved for all three ecosystems in July. Soybean and switchgrass peak fluxes did not differ (8.1 and 7.6 µmol m ⁻² s⁻¹ respectively) with cottonwood peak flux differing from other treatments (6.1 µmol m ⁻² s⁻¹; p < 0.01). Peak fluxes for 2013 were achieved in May for both switchgrass and cottonwood (5.91 and 4.11 µmol m⁻² s⁻¹, respectively), where the switchgrass peak flux was larger than that for cottonwood and the agroecosystem, which did not differ (p < 0.01). Annual CO 2 emissions differed among ecosystems (p < 0.001), but not between years (p = 0.45). Cottonwood had less CO 2 emitted for both years (7.3 and 7.4 Mg ha⁻¹ for 2012 and 2013, respectively) compared to the other two ecosystems, while emissions from the switchgrass did not differ from soybean in 2012 (10.3 and 9.5 Mg ha⁻¹, respectively) or grain sorghum in 2013 (9.7 and 9.2 Mg ha⁻¹, respectively). Results showed established bioenergy feedstock cropping systems do not have greater soil respiration rates compared with a traditional soybean-grain sorghum crop rotation. Results also indicated that different bioenergy feedstocks can produce different quantities of CO 2 emissions. Both factors are important to consider when enrolling marginal land in the LMAV in bioenergy feedstock cropping systems.

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