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Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - April 2022)
Declining land productivity associated with decreasing soil organic carbon (SOC) and nitrogen (N) is an issue for conventional production of small grains. Intercropping grains with legumes may provide a sustainable solution. I grew wheat (Triticum aestivum cv. ‘Scarlet’) as a monoculture and intercropped with either common bean (Phaseolus vulgaris cv. ‘Red Kidney’, or cv. ‘Black Turtle’), or fava bean (Vicia faba cv. ‘Bell’) in rows of wheat:bean 1:1 and 2:1 as well as broadcast arrangements to assess the effects of genotype and spatial arrangements on crop agronomy, land productivity, biological nitrogen fixation and transfer, N and carbon (C) accumulation in aboveground biomass, soil N balance, gross ecosystem photosynthesis (GEP), net ecosystem productivity (NEP), and water use efficiency (WUE). Barley (Hordeum vulgare cv. ‘Oxbridge’) and pea (Pisum sativum cv. ‘Reward’) were also included based on synchronized maturity, yield potential, protein content, and root architecture. Stable isotope methods (¹³C and ¹⁵N) coupled with field CO₂ exchange measurements were used to determine C and N transformations.Intercrop plots had higher land productivity, improved grain and biomass quality, increased legume nodulation and percent N derived from symbiotic N₂ fixation. Wheat-fava bean in the 1:1 arrangement displayed a 50% increase in land productivity. Barley-pea in the 2:1 arrangement also had the highest total land outputs (5.9 t ha-¹) and land equivalent ratio (1.32). Wheat-fava bean in the 1:1 arrangement fixed the highest amount of N (74 kg N ha-¹), transferred the most N (13% of N in wheat), and accumulated more C (26% higher than wheat monoculture) in shoot biomass. WUE of wheat was improved when grown with fava bean. Pea in intercrop plots also displayed increased nodulation (27-45%) and symbiotic N₂ fixation (9-17%) leading to the addition of 60-78 kg N ha-¹. The GEP and NEP were highest in the 2:1 arrangement and led to the highest daytime C sequestration (229 mg C m-² hr-¹).I demonstrated that intercropping small grains with legumes, in specific spatial arrangements and under low input organic conditions, can counter conventional monoculture-associated SOC and N losses through higher land and ecosystem productivity, and greater organic N-fixation and transfer.
Master's Student Supervision (2010 - 2021)
Management of our agroecosystems faces a dual problem where we need to produce more food, fiber and fuel with the same amount of land while limiting the impact of this production on the earth’s biodiversity and environment. A solution to this problem is to manage agroecosystems for augmented biodiversity to increase the provision of Ecosystem Services (ES). Increasing on-farm diversity can improve ES beyond the provision of food to help reduce the use of environmentally costly inputs through ES provision such as growing nitrogen-fixing plants to supply nitrogen to food crops in lieu of other inputs. Cover crops are plants that can be grown temporal or spatially isolated from food crops with limited negative impacts on yield and can provide significant positive impacts to both the farmer’s profitability and the environment. Increasing the biodiversity of cover crops is one key strategy to sustainably intensify agriculture by helping to improve yields while limiting the environmental impact of agricultural production. To determine if increasing cover crop biodiversity leads to greater ES provision, experiments were conducted that manipulated cover crop functional diversity in three settings, a field trial at the UBC Farm, a pot experiment in the UBC Horticultural Greenhouse, and a litter-bag study at the UBC Farm. A functional group framework was applied to cover crops using a grass (Rye Secale cereale L.), a legume (Lana Vetch Vicia villosa ssp. dasycarpa Roth.) and a forb (Chicory Cichorium intybus L.) in mixtures of varying degrees of diversity. The general conclusion from these analyses was that mixtures were capable of providing a comparable magnitude of ES to the best monoculture while providing a range of ES greater than any one monoculture. In monoculture, rye was the best for carbon fixation (biomass production and CO₂ uptake) and weed suppression; Lana vetch was the best for improving soil fertility (nitrogen and phosphorus release); and chicory was the best for soil cover (leaf area) and residue decomposition. There was sufficient evidence to support the use of cover crop mixtures to provide ES that reduce the environmental impact of agricultural production with potential to improve crop yields.
Increasing food insecurity, lack of sustainable food systems, and a desire to participate in the food system are prompting the growth of various forms of urban agriculture: community gardens, urban homesteads, and urban farms. Urban farms, as distinct from other urban agriculture projects, are defined by the sale of their product. They raise produce and grow ornamentals to sell in neighbourhoods, all while building urban food networks that connect communities to their food. Resilient localized food production systems must be economically, socially, and environmentally sustainable to succeed in a changing environment. Research on urban agriculture has largely focused on community gardens and their social benefits, leaving little known about entrepreneurial urban farms. This study examines the business models and economics of Metro Vancouver’s urban farms through a newly developed tool, the ‘Urban Farming Census.’ The use of this semi-structured interview tool revealed revenues, costs, financing, and sales models of urban farmers as well as their community connections and benefits. The Urban Farming Census was applied during the 2010 and 2011 growing seasons, capturing the first attempts by Vancouver’s urban farming organizations growing sustainable businesses. In 2010, eight urban farms produced $128,000 worth of produce on 2.31 acres, supporting 17 paid employees. In 2011, ten urban farms sold $170,000 worth of produce on 4.19 acres, supporting 30 paid employees. Urban farms do more than sell produce; they educate their communities about food production and provide space for individuals and communities to explore their intergenerational, multicultural food cultures.
Low-cost hoop houses are common climate enhancing structures used by small to medium-scale farmers for intensive production of high-value crops. On-farm fertilizer production and utilization of locally available soil amendments can reduce input costs, while increasing regional sustainability. Production system specific organic fertilization programs, with respect to relative nutrient concentrations, mineralization rates, and pest and disease suppressing capabilities, are crucial for sustained high yields. The objectives of this study were to assess organic fertilizer source effects on protected, organic Solanum lycopersicon L. (tomato) production in South Coastal British Columbia, and to assess whether genotype x fertilizer source interactions are present for various growth and yield traits. Two cultivars of tomato, cv. Black Cherry and cv. Pollock were grown in a randomized complete block, split plot design, consisting of four fertilizer treatments replicated three times. Fertilizer treatments included: 1) Vicia villosa Roth. (hairy vetch) green manure (HV), 2) composted poultry manure (CPM), 3) Ecofert® ‘EcoGrow’ 3-3-4 (OMRI certified) liquid fertilizer, and 4) a no treatment control. All fertilizers were applied at a rate of 100 kg total nitrogen per hectare. Treatments had no effect on vegetative growth, except increased biomass in cv. Pollock treated with EcoGrow. Yield responses in cv. Black Cherry commenced from harvest week six onwards for CPM and HV treatments and from week eight for EcoGrow. By seasons end, all fertilizer treatments produced yield increases of 23% over the control in cv. Black Cherry plants while no yield response occurred in cv. Pollock. Both EcoGrow and HV had positive effects on foliar potassium, which was the most limiting nutrient. Total soil nitrogen and available phosphorus were considered sufficient, except foliar phosphorus was near the critical level at mid-harvest in all treatments. Foliar calcium and magnesium were high. Several fungal diseases, including late blight, powdery mildew, grey mould and verticillium wilt, infected the crop from mid-July and may have affected plant nutrition and yield. This study shows that a range of organic fertility sources can be effectively used in protected tomato production. However, cultivar lifecycle and growth habit should be considered when devising fertilization programs.