Graduate Thesis Or Dissertation
 

Cover crop effect on soil microbial biomass after fumigation in potato fields in the Columbia Basin

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/7h149z24v

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  • In the Columbia Basin, pre-plant soil fumigation is commonly used in potato production for pest control, but fumigation can kill non-target organisms within the soil, result in unintended shifts in the microbial community, and disrupt long-term soil health. Cover crops have been shown to strongly influence the numbers and communities of microorganisms within the soil and, if used properly, may help improve soil microbial biomass after fumigation. However, little information is available on how soil fumigation and cover crops impact soil health in potato fields. To fill this knowledge gap, this thesis focused on determining the interactive effects of soil fumigation and cover crops on 1) microbial population numbers and 2) potato yield and quality. To meet our objectives, two experiments (one field trial and one greenhouse experiment) were conducted. The fumigation treatments included no fumigation (control), Telone (1,3-dichloropropene), metam sodium, and the co-application of Telone+Metam sodium. The five cover crop treatments included no cover crop (control), wheat (Triticum aestivum), mustard (Brassica nigra), radish (Raphanus sativus), and winter pea (Pisum sativum)+fava bean (Vicia faba) mixture. The field study was performed at the Hermiston Agricultural Research and Extension Center, in Eastern Oregon. The experimental design was a split-plot design arrangement with four replicates. The main plot corresponded to fumigation treatments and subplots were cover crops. Soil fumigation was conducted on September 30, while cover crops were planted on Oct. 15. Cover crop biomass was measured, and soil samples were taken before termination of the cover crops. After the cover crop were integrated into surface soil, the field was prepared for sowing potatoes. In unfumigated soils (control), the analysis of microbial biomass carbon revealed a trend of more mean MBC for all cover crop types, except mustard, than control by 41%, 37%, and 31% for pea/fava bean, wheat, and radish, respectively. In soils treated with metam sodium, mean MBC was greater with the inclusion of cover crop and resulted in 30%, 34%, 41%, and 40% significantly more MBC respectively than the control, for pea/fava bean, wheat, radish, and mustard treatments. In soils treated with Telone fumigation, mean MBC was found to be greater with no cover crop than plots without cover crops (37% and 19% greater than wheat or mustard, respectively). The yields of premium potatoes (tuber size larger than 6 oz) were higher in the fumigated plots than in the non non-fumigated plots. Soil fumigation tended to increase potato specific gravity especially with metam sodium fumigants. However, the effect of cover crops on potato yields were limited regardless fumigation or not, most possibly because their biomass were small when they were planted at late fall . No significant differences were found in potatoes for size class or internal defects between treatments. The greenhouse study was conducted at Oregon State University in Corvallis, OR. The experimental design was a factorial completely randomized design with fumigation and cover crops (listed above) as factors. There were no differences among treatments for MBC or potato yield were found between the treatments. This research revealed that (1) there were differences found in the microbial numbers generated by the inclusion of cover crops following fumigation in the short term; (2) differences were not found in potato yield and quality with the inclusion of cover crops following fumigation in the short term. This experiment must be repeated for additional years to assess the long-term impacts of cover crops on microbial numbers following fumigation.
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  • Washington Specialty Crop Block Grant Program
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