UBC Theses and Dissertations
Linking soil biotic and abiotic factors to sweet cherry tree establishment in new and old Okanagan Valley orchards Munro, Paige
In the Okanagan Valley of British Columbia, sweet cherry (Prunus avium L.) has traditionally been replanted into soil that previously supported tree fruits. However, growth of young fruit trees replanted into old orchard soil is often poor and thought to be due to plant-parasitic nematodes (i.e. Pratylenchus spp.) and fungi. Due to climate change, cherry production is expanding into northern and higher elevation areas of this region that were not previously cultivated to tree fruits. Models have considered how climate and soil physicochemical properties will influence cherry range expansion, but they have not considered soil biology. The first objective of this study was to compare soil from 18 old (n=12) and new orchard soils (n=6) with respect to the influence of soil biology on cherry growth, by measuring plant growth response to sterilization in a bioassay, and to determine which biotic and abiotic properties best predict cherry growth among this array of orchard soils. Shoot height increment was significantly greater in untreated (non-sterilized) new soil relative to old soil where microbial activity was reduced (sterilized). According to multiple regression, the variables FDA hydrolysis, organic carbon, and sodium were positive predictors of plant growth for both new and old soils. Using greenhouse and field experiments, the second objective of this study investigated how compost and woodchip mulch application affected soil biotic and abiotic properties compared to non-amended soil in two new, northern, and two old, central Okanagan sweet cherry orchards over two growing seasons. In the field study, compost-amended soil resulted in greater soil nutrient status at all four orchards, but there were few effects on soil biological properties. In the greenhouse study, amended soil from both new sites and one old site resulted in lower Pratylenchus root colonization than non-amended soil. Overall, results from these experiments suggested that (1) new orchard soils are ‘biologically suitable’ for planting sweet cherry, and (2) compost application may be a tool to maintain soil health, and mitigate future soil-borne disease in old, replant stress-prone sites, as well as in newly established orchard soils that have never cropped sweet cherry or other tree fruits.
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