Date of Award


Document Type


Degree Name

Master of Science (MS)


Plant and Soil Science

First Advisor

Deborah A. Neher

Second Advisor

Jeanne M. Harris


Manure-derived organic amendments are a cost-effective tool that provide many potential benefits to plant and soil health. For example, amendment applications may increase soil fertility, improve soil structure, stimulate microbial activity, and suppress plant pathogens. Yet, responses to these applications may have unintended consequences. Inherent variability in the physical, chemical, and biological characteristics of these materials can result in inconsistent outcomes observed after their application. These differences are manifested in plant growth, soil physiochemical properties, and soil microbial community composition. Popular manure-derived organic amendments include dairy manure compost and poultry manure pellets. Dairy manure is an abundant resource on many diversified farms and poultry manure pellets are an economical and commercially available source of nitrogen. Despite a growing body of research demonstrating the plant growth enhancing and disease suppressing potential of vermicompost, its’ relative price and availability has limited its widespread adoption in field-grown vegetable production systems. Additional research which determines how and why vermicompost performs differently than alternative amendments is necessary to justify its greater adoption. A container study was conducted to evaluate how dairy manure compost, dairy manure compost-derived vermicompost, and dehydrated poultry manure pellets impact the tripartite relationship among plant growth, soil physiochemical properties, and microbial community composition. Organic amendments increased soil porosity and soil water holding capacity but delayed plant maturation and decreased plant biomass. Of those treated with organic amendments, vermicompost-amended plants displayed the greatest root growth and overall plant health through time. Distinct microbial communities were detected for each treatment, with an abundance of Massilia, Chryseolinea, Scedosporium, and Acinetobacter distinguishing the control, vermicompost, dairy manure compost, and dehydrated poultry manure pellet treatments, respectively. Known ecological roles of these organisms support the observations made in this study: Massilia and Chryeolinea promote plant growth, Scedosporium abundance reflects the immaturity of the dairy manure compost provided, and Acinetobacter, among several taxa present in the poultry pellet-amended treatment, highlights existing concerns about the safety of poultry manure-based fertilizers in agriculture. This study validates that organic amendments alter the rhizosphere microbiome by influencing plant growth and soil physiochemical properties. In addition, this study highlights the impact of organic amendment application on the physical soil environment and the influence this change has, both directly and indirectly, on soil microbial community composition. Furthermore, this study demonstrates that there is a strong interaction between root growth and the spatial heterogeneity of soil and root-associated microbial communities. The varied response to organic amendment application in this study demonstrates that a more comprehensive characterization of these materials, and their impact on the soil environment, is required to successfully utilize these products in an effort to improve soil health and modify soil microbial communities. While highlighting a widespread need for additional research, this study serves to suggest that vermicompost is a valuable tool to promote plant health and manage disease and supports the adoption of a vermicomposting curing step to stabilize manure-derived fertilizer products.



Number of Pages

119 p.