Date of Award
12-2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Plant and Environmental Science
Committee Chair/Advisor
Dr. Vidya Suseela
Committee Member
Dr. Nishanth Tharayil
Committee Member
Dr. Rongzhong Ye
Committee Member
Dr. William Bridges
Abstract
Soil degradation is a major global issue that negatively affects environmental quality and food production. Maintaining continuous soil cover helps prevent erosion and supplies food for soil microorganisms, including arbuscular mycorrhizal fungi (AMF). In the United States, most grain and feed crops are annuals. After harvest, fields often remain bare from late fall through early spring, during which wind and rainfall can erode unprotected topsoil. Due to this vulnerability, economic and sustainable strategies are necessary to protect the soil between cash crops. One widely promoted approach is planting cover crops instead of leaving the land fallow during winter.
Beyond preventing erosion, cover crops also help mitigate the drawbacks of monocropping—one of the most common agricultural practices in the U.S. Increasing crop diversity using different cover crop species can disrupt pest cycles and support a more diverse soil microbial community. Cover crops produce substantial above- and belowground biomass that helps interrupt monocropping cycles. After harvest, their roots continue to decompose, providing a steady supply of energy for beneficial soil microbes. In this way, cover crops not only conserve soil but also contribute to long-term increases in soil carbon and organic matter. Cover crops can also be grown as mixtures of different plant functional types (PFTs), further enhancing crop rotation diversity.
We conducted field and greenhouse experiments to evaluate how cover crops, grown in monocultures and mixtures, influence 1) AMF associations, 2) soil microbial extracellular enzyme activity (EEA), and 3) the contributions of different cover crop tissue types to EEA and soil-available nutrients. We used cover crop species commonly planted in South Carolina, representing legumes, grasses, and brassicas. Our mixtures included a three-species combination containing one species from each PFT, and a five-species mixture consisting of three legumes (chosen for functional redundancy), one grass, and one brassica.
We found that cash crops grown after cover crops exhibited greater AMF colonization than those grown after bare fallow, and the magnitude of this effect differed by cover crop species. Cover crops also stimulated enzymes involved in cycling major nutrients—carbon, nitrogen, and phosphorus. Additionally, shoot and root tissues contributed differently to nutrient pools and enzyme activity: aboveground biomass provided readily decomposable material that supported microbial activity, while roots influenced subsurface processes and sustained nutrient cycling during the decomposition process.
This study underscores the importance of adopting cover cropping practices and selecting appropriate species—preferably in diverse mixtures. We recommend that farmers utilize cover crops as a sustainable tool to support soil microbial health, enhance cash crop productivity, and reduce their reliance on inorganic fertilizers.
Recommended Citation
Sultana, Sifat, "Impact of Cover Crop Functional Types in Monocultures and Mixtures on Mycorrhizal Fungi and Soil Microbial Functional Activity" (2025). All Dissertations. 4106.
https://open.clemson.edu/all_dissertations/4106