Dissertation
GREEN MANURES AND BRASSICA SOIL AMENDMENTS FOR SOIL HEALTH AND SOIL MICROBIAL COMMUNITY IN DOUGLAS-FIR NURSERIES AND POTATO
Doctor of Philosophy (PhD), Washington State University
01/2016
Handle:
https://hdl.handle.net/2376/111548
Abstract
Incorporation of organic soil amendments in the form green manures (GM), composts, and crop residues is believed to enhance soil quality and crop performance. Field studies in Washington evaluated the effects of various green manures and brassica seed meal on beneficial soil organisms, soilborne pathogens, and soil quality in two different cropping systems. Damping off in Douglas-fir (Pseudotsuga menziesii) and early dying in potato (Solanum tuberosum) are two major threats in their respective crops. Chemical fumigation with methyl bromide in Douglas-fir nurseries and metam sodium in potato fields have been major control tactics. Due to safety and environmental concerns, these chemicals have been increasingly restricted. In Douglas-fir field study, Fusarium spp. density was significantly lower after Brassica juncea GM incorporation [1.8 log CFU (colony forming units) g-1 soil] than after chemical fumigation (2.4 log CFU g-1 soil) or in the untreated control (2.6 log CFU g-1 soil). The soil density of potentially antagonistic Trichoderma spp. was greatest in chemically fumigated plots followed by B. juncea GM treatment and lowest in untreated control soil at mid-season. B. juncea GM treatment also produced significantly larger seedlings than the untreated control treatment. Dehydrogenase enzyme activity, water holding capacity, and nitrogen mineralization were significantly greater in GM treatments compared to untreated control and chemical fumigation treatments in most
years and sites in both studies. The results showed a significant improvement in soil quality with brassicaceous soil amendments in conifers and with both brassicaceous GM and barley GM treatments in potato compared to untreated control and chemical fumigation.
High-throughput DNA sequencing was also used to determine treatment effects on soil bacterial communities. Non-metric multidimentional scaling showed different frequencies of certain microbial groups in the various treatments. Some potentially beneficial genera such as Lactobacillus and Exigobacterium were enriched in GM treatments compared to untreated control and fumigation treatments. The incorporation of organic soil amendments seems to be a promising practice for long-term soil management and will help maintain or improve soil health, beneficial soil microbiomes, and crop performance.
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Details
- Title
- GREEN MANURES AND BRASSICA SOIL AMENDMENTS FOR SOIL HEALTH AND SOIL MICROBIAL COMMUNITY IN DOUGLAS-FIR NURSERIES AND POTATO
- Creators
- Bodh R. Paudel
- Contributors
- Lynne A Carpenter-Boggs (Advisor)Scot H Hulbert (Committee Member)Dennis A Johnson (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Crop and Soil Sciences
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 142
- Identifiers
- 99900581721501842
- Language
- English
- Resource Type
- Dissertation