Document Type

Dissertation - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Plant Science

First Advisor

James J. Doolittle


The dynamics of soil organic carbon (SOC) play an important role in long term agroecosystem conservation and productivity, and the emission of greenhouse gases. Soil is an important component in the global C budget and C sequestration in soil can be maximized by adoption of appropriate management practices. The objectives of this study were i) to evaluate the long-term impact of switchgrass (Panicum virgatum L.) in Conservation Reserve Program (CRP) land and of agricultural practices in agricultural crop production (ACP) land on soil physical properties and C storage, ii) to determine the active C pools related with C mineralization, and iii) determine the effects of fertilization and harvest on the seasonal changes in soil respiration and soil biological C fractions. Three South Dakota soil series were selected to evaluate the long-term impact of switchgrass on C storage and soil physical properties: Egan (Udic Haplustolls), Ree (Typic Argiustolls), and Buse (Typic Calciudolls). The soil respiration study was done in the switchgrass land of the Egan series soil. Soil bulk density was significantly lower in the CRP land and water stable aggregation was significantly increased in the CRP land when compared to ACP land. Egan mean SOC values in the top 30 cm were 91.3 Mg ha-1 and 57.5 Mg ha-1 for CRP and ACP lands, respectively. Ree mean SOC values in the top 30 cm were 53.4 Mg ha-1 and 34.3 Mg ha- 1 for CRP and ACP lands, respectively. No significant SOC difference was found between treatments in the Buse soil. The results of this study show that the reestablishment of a perennial grass land from ACP land can increase soil C sequestration and improve soil physical properties. Potentially mineralizable C (PMC) had the strongest correlation with soil microbial biomass C (SMBC) (r = 0.905) and particulate organic C (POC) (r = 0.840). There was also a strong correlation between SMBC and POC (r = 0.900). For a single-predictor regression model, PMC was the best predictor (r2 = 0. 739) of in-situ CO2 evolution. Soil respiration, PMC, and SMBC were not significantly affected by N and P application. Manure application significantly increased soil respiration, PMC, SMBC and SOC. Soil organic C increased by 0.14 kg C m-2 y-1 with a manure application of 0.79 kg C m-2 y-1. Switchgrass harvest significantly decreased soil respiration in the first harvest year and did not significantly impact soil respiration the following year. Soil respiration rates per unit soil organic C content in the soybean field were 44% higher than that in the switchgrass field. Results show that fertilization did not significantly impact soil respiration in the first two years of biomass production in the high organic C grassland.

Library of Congress Subject Headings

Soils -- Carbon content.
Carbon sequestration.
Grassland conservation.


South Dakota State University



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In Copyright