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UBC Theses and Dissertations

Soil, crop yield, and cost trade-offs of organic nutrient management strategies across mixed vegetable farms in southwest British Columbia Norgaard, Amy


Nitrogen (N) and phosphorus (P) are essential for crop growth but degrade the environment when lost from farming systems. While conventional farms have capacity to precisely calculate nutrient budgets based on the nutrient content of synthetic fertilizers, organic nutrient sources have inconsistent and difficult to predict nutrient supply. The objectives of this study were to: (1) inventory amendment and soil properties across three regions of southwest British Columbia (lower Fraser Valley (FV), Pemberton Valley (PV), and Vancouver Island (VI)), and (2) evaluate effects of three nutrient management strategies on 20 farms across these regions on crop yields, economics (input costs), and selected soil properties (permanganate oxidizable carbon (POx-C), post-season available N and P). Nutrient strategies evaluated were: ‘high compost’ (HC): compost applied to meet crop N removal, ‘low compost + N’ (LC+N): compost applied to meet crop P removal plus an organic fertilizer to meet crop N removal, and ‘typical’ (TYP): the typical nutrient application used by the farmer (varying combinations of composts and organic fertilizers). While I found no differences in POx-C among nutrient management strategies, I did find HC had higher yields in the FV. However, principal components analysis (PCA) showed that HC was also associated with high post-season available N when high N composts and manures were used. Input costs tended to be least expensive in the lower Fraser Valley region, where TYP was less expensive than either HC or LC+N. The PCAs also showed that there was enhanced yield and POx-C values with LC+N when composts with high carbon to N ratios (C:N) were used. However, in regions where high nutrient composts are relatively inexpensive, productivity and economic incentives encourage practices that contribute to high soil P and post-season available N. The results of this study highlight the trade-offs between environmental and economic goals; even though organic farmers have land stewardship in mind, decisions are still largely influenced by economic principles, while in the bounds of organic regulations.

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