Graduate Thesis Or Dissertation

Effects of Biochar and Nitrogen-Enriched Soil Amendments on Plant Growth, Mineral Nutrition, and Early Fruit Production in Highbush Blueberry (Vaccinium sp.)

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  • The goal of the work in this dissertation was to identify alternative soil amendments to improve plant growth and yield during establishment of highbush blueberry (Vaccinium hybrid). Woody materials, such as sawdust and wood chips, have a high carbon to nitrogen (C:N) ratio and low water holding capacity, which can limit N availability and reduce the growth and fruit yield of highbush blueberry during establishment. This is the case in the Pacific Northwest where douglas fir [Pseudotsuga menziesii (Mirb.) Franco] sawdust is a readily available, low-cost source of organic matter. Growers incorporate additional fertilizer at planting to reduce N immobilization; however, this raises production costs and does not increase nutrient or soil moisture retention. The use of alternative materials such as biochar as a soil amendment could increase nutrient retention and soil moisture. Organic materials with a high C:N ratio are often used to adsorb excess N from water bodies, which increases N concentrations of the materials, allowing them to act as slow-release N fertilizers. These enriched materials could also serve as soil amendments. However, neither biochar nor N-enriched materials have been used to grow blueberry. To address these issues, three studies were conducted from 2016 to 2018 in both greenhouse and field conditions in western Oregon. In the first study, we investigated the potential of using biochar, alone or in combination with bokashi, as a soil amendment for ‘Legacy’ blueberry. Bokashi is the decomposition of waste through fermentation. We found that biochar increased plant growth when fertilized weekly with a complete fertilizer (30N–10P–10K) and 600 ppm ammonium sulfate once a month. However, bokashi was more beneficial for plant growth when nutrients were limited. Biochar did not suppress infection by Phytophthora cinnamomi Rands, but it increased root colonization by ericoid mycorrhizal fungi. In the second study, a 2-year field experiment was conducted to determine whether amending soil with biochar or biochar and bokashi alters growth and early fruit production during establishment of ‘Duke’ blueberry. Plants grown in soil amended with biochar grew more in the first season, resulting in greater yield in the second season than those grown with no amendments or in soil with sawdust only. In contrast, sawdust limited plant available N, resulting in N-deficient plants. Furthermore, adding biochar to the planting hole was considerably more economical than applying it to the row and was more economical than the industry standard of incorporating sawdust in the row. In the third study, red alder (Alnus rubra Bong.) sawdust, douglas fir sawdust, shavings, and wood chips, biochar, and yard-debris compost were untreated or enriched with ammonium-N and evaluated as soil amendments in ‘Duke’. Plants grown with enriched amendments had greater shoot dry weight and a greater concentration of N in the leaves than those grown in unenriched amendments, regardless of whether or not they received additional N fertilizer. Overall, amending soil with biochar or N-enriched organic materials appear to be a promising means for improving plant growth, mineral nutrition, and early fruit production in highbush blueberry.
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