Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Plant Pathology and Microbiology

First Advisor

A. H. Epstein

Second Advisor

D. C. Norton


Use of manure and compost as soil amendments has been proposed as a way to reduce farm input costs, waste disposal problems, and groundwater pollution, and at the same time control plant disease. The objective of this research was to compare the ability of fresh and composted manure to induce suppression of Rhizoctonia solani Kuhn;Soil in microplots was amended with urea, dairy manure, and composted dairy manure, infested with sclerotia of R. solani, and planted with beans. Infestation and planting were repeated two more times. Seedling emergence was greatest in soil amended with manure, and least with urea. Freedom from visible lesions and yield of plant tops were also greatest for plants grown with manure. Soil media in the greenhouse were amended with urea, urea and straw, manure, and compost. All four amendment rates were chosen to provide 75 ppm nitrogen; the latter three amendments added 0.3% organic matter to the soil media. After a 1-week incubation, soil mixtures were infested with 0, 10, 20, or 30 Colony Forming Units (CFU)/g R. solani sclerotia and then planted with radish four times. Radish Health Index (RHI) was used to compare treatment effects on disease. A large value for RHI indicated high levels of seedling emergence and a small size for any lesions. RHI was greatest for seedlings planted with urea and straw, less with manure or compost, and least with urea alone. RHI with urea and straw was greater at all infestation levels than with other amendments, but at 20 and 30 CFU/g infestation, RHI did not differ among the other three amendments. Despite the differences in RHI, the recovery of R. solani in heat-killed beet seed baits did not differ among treatments;In conclusion, all soils became suppressive, but amendments affect the rate at which suppressiveness develops and disease suppression does not imply pathogen suppression. Manure is more effective than compost in suppressing disease at low inoculum levels, but neither amendment is effective at high inoculum levels. Because manure can reduce plant disease better than urea, the value of amending soil with manure exceeds the fertilizer benefit.



Digital Repository @ Iowa State University,

Copyright Owner

Rickie Paul Voland



Proquest ID


File Format


File Size

101 pages