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ADVICE AND INSIGHTS FROM UBC FACULTY ON REACHING OUT TO SUPERVISORS
These videos contain some general advice from faculty across UBC on finding and reaching out to a potential thesis supervisor.
Graduate Student Supervision
Doctoral Student Supervision
Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
Improving agricultural phosphorus management to reduce environmental loss in high phosphorus soils in the Fraser Valley, British Columbia (2024)
Soil phosphorus (P) has reached environmentally concerning levels in the Fraser Valley, one of the most intensively farmed areas of British Columbia (BC), due to the repeated, excess application of P as manure and mineral fertilizers. To help address the potential risk of P losses to aquatic ecosystems, it is crucial to account for both crop production and environmental protection objectives. In this dissertation, I aimed to develop strategies and tools to improve P management and monitor environmental P risks associated with agricultural land with high soil test P (STP) in the Fraser Valley. Two-year field trials were established in eight sites in 2020 and 2021 to investigate the effects of increasing starter P rates on silage corn growth and phosphate availability during the growing season. Results showed that starter fertilizer P, at any application rate, in high-P manured soils does not improve silage corn yield; farmers applying manure at ploughing in soils with high P concentrations can reduce or eliminate starter fertilizer P without impacting silage corn yields, decreasing the reliance on off-farm P inputs and reducing potential P loss to the environment. This research also investigated how increasing soil pH with lime could affect agri-environmental P risk indicators and P sorption characteristics. Increasing soil pH with lime did not affect the degree of P saturation (DPS), and P saturation index (PSI) but showed decreasing trends of Mehlich-3 extractable P and water extractable P (Pw) concentrations even though the extent was only significant for Pw in soils with initial pH = 5.8, indicating a reduced risk of P loss when soils are limed. I used the results of these two studies to develop a tool for monitoring environmental P risk by identifying four specific environmental P risk classes, namely low, moderate, high, and very high with the moderate PSI and Pw limits = 6.6-10.8% and 2.2-4.1 mg kg⁻¹, respectively. This dissertation contributes to our understanding and application of P risk indicators to quantify and monitor the risk of P loss to improve fertilizer and manure management in high P-affected areas of the Fraser Valley.
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Digital soil mapping to enhance climate change mitigation and adaptation in the Lower Fraser Valley using remote sensing (2020)
Globally, the agriculture sector is constantly being challenged by multiple climate change-induced stresses while agricultural activities are responsible for a large portion of global greenhouse gas emissions. At the same time, agroecosystems have a sizable potential to mitigate climate change through the sequestration of atmospheric carbon-dioxide as soil organic carbon (SOC); a key soil quality parameter that can also enhance climate change adaptation. Although the dual benefits of SOC are well established, intensive agricultural production and associated land use/land cover (LULC) changes continue to drive large declines in SOC. Alternatively, sustainable LULC practices can potentially reverse this trend and improve SOC stocks. Digital soil mapping (DSM) using remote sensing can help elucidate SOC dynamics associated with LULC change and agricultural management practices by producing spatially explicit information on SOC at the field- and landscape-scales. In this research, I developed and applied innovative DSM techniques to study the spatiotemporal changes in SOC and related soil properties in the Lower Fraser Valley (LFV), one of the most intensive agriculture regions of British Columbia, Canada. At the field-scale, I evaluated various sampling strategies for DSM using unmanned aerial vehicle imagery, mid-infrared spectroscopy and geostatistical models to identify the most cost-effective approach. At the landscape-scale, using Landsat satellite imagery and machine learning tools, I produced maps of soil workability thresholds (WT) for the agricultural lands in Delta and then, assessed the SOC dynamics across the entire LFV since 1984. My analysis identified that 40% of Delta’s agricultural lands had a WT of 30%, making them extremely vulnerable to the shifting precipitation patterns expected for the region. In addition, 61% of LFV lost SOC, 12% of the region gained SOC, while 27% remained unchanged between 1984 and 2018. Areas that lost the most SOC were those that had experienced changes in LULC; however, I concluded the majority of SOC loss occurred due to agricultural practices. The dissertation contributes to devising cost-effective approaches to quantify and monitor changes in SOC at the field- and landscape-scales that can help in the development of effective agricultural climate change mitigation and adaptation strategies.
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Integrating field and remote sensing approaches to evaluate ecosystem services from agriculture in smallholder landscapes (2017)
Agriculture now covers over a third of the Earth’s terrestrial surface, and smallholder farmers alone manage over a billion hectares globally. As stewards of the land, smallholders do much more for human well-being than just harvest useful products. However, a conventionally narrow focus on productivity over the last half- century now threatens ecosystem health and long-term agricultural production, particularly as global climate change accelerates. Agroecological and ‘climate-smart’ agricultural (CSA) practices have been proposed to both mitigate climate change and build resilience by enhancing multiple ecosystem services (ES), and policies are emerging to incentivize the adoption of such practices. In order to (1) better understand how agroecological and CSA management alternatives impact multiple ES, and (2) contribute to operationalizing monitoring of ES in smallholder landscapes, I present research from El Salvador combining field methods and remote sensing analysis to evaluate multiple ES. Using data from on-farm field trials, I developed composite ES indices to demonstrate distinct benefits and synergies among multiple ES from agroforestry and, to a lesser extent, organic management (i.e., CSA) compared to conventional management. I also identified a subset of easy-to-measure field proxies that correlate well with multiple ES, and proposed an improved method to compare relative erosion resulting from different land management practices. At the landscape scale, I focused on emerging techniques to map aboveground woody biomass (AGWB) – a large terrestrial carbon sink and indicator of agroforestry management – using high-spatial-resolution satellite imagery and airborne laser scanning (ALS). I showed how satellite data could be used to quantify AGWB at the watershed to landscape scale with uncertainties of less than 5%, and suggest that a singular focus on plot-scale uncertainty limits the operationalization of satellite-based approaches to monitor AGWB. I also present a novel approach to using ALS that improves the accuracy of measuring AGWB in trees outside of forests (e.g., agroforestry, hedgerows) and apply it to show that these trees contain substantial AGWB within smallholder landscapes, further demonstrating the ES benefits of agroforestry. This dissertation contributes to designing simple and cost-effective monitoring strategies to help operationalize policies promoting management practices that enhance multiple ES in smallholder agriculture.
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Master's Student Supervision
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Pig grazing as a regenerative alternative to tillage in market crop production: comparing cover crop growth and soil health indicators (2024)
Cover crops are routinely used on farms to increase soil fertility, protect from erosion, and improve productivity. These green manure crops are predominantly managed with mechanical implements, which can cause adverse impacts on soil properties such as compaction, erosion, organic matter losses. The objective of this study was to investigate the viability of replacing tillage by using strip grazing pigs to manage cover crops (terminate and re-seed via trampling) and compare their impacts on cover crop growth and soil health to a system using typical tractor tillage. The experiment was conducted twice on two different areas of the same farm, one left fallow for 5 years, the other under previous organic market crop production. It was observed that cover crop coverage was 48% higher on average in the grazing system during the summer season and 35% more higher after a winter of growth. The proportion of weed cover varied according to the preceding land use; significantly more weeds were found in the tillage system where cropping activities had taken place before. Penetration resistance was significantly lower in the grazing system at the 15-30 cm depth which suggests it helped mitigate the plough pan layer. Mean aggregate stability was higher in the tillage system due to a higher fraction of macroaggregates even though there was a significantly higher fraction of microaggregates in the grazing system. Bulk density was not found to be significantly different between systems, but volumetric water content was significantly lower in the grazing plots. Nitrate levels were significantly higher in the grazing system, but grazing did not affect levels of ammonium, phosphorous, and permanganate oxidable carbon. Soil respiration was found to be significantly higher in the grazing system and mean earthworm count and weight were also 41% and 86% respectively. Overall, this study indicates that using grazing pigs to manage cover crops is a promising strategy that may help to prevent some of the negative impacts of tillage, even if used only over one growing season.
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Impacts of field hydrology management on two years of soil greenhouse gas emissions from blueberry crop rows in Delta, British Columbia (2023)
An observational study was conducted to investigate the potential of managing field hydrology to reduce soil greenhouse gas emissions (GHG) from blueberry crop rows on silt loam soils in a temperate maritime climate. Results from the field study were used to validate three models: the tier 1 IPCC and tier 2 equation by Rochette et al. (2018), which are used to estimate annual soil nitrous oxide (N₂O) emissions, and the tier 3 Denitrification-Decomposition model (DNDC) which simulates daily soil emissions of carbon dioxide (CO₂), N₂O, and methane (CH₄). Soil emissions were measured every two weeks for two years, using dynamic closed chambers in nine fields, which were either (1) undrained, (2) drained with subsurface tiles, or (3) drained with subsurface tiles and ditch pumps. Drainage system did not impact field hydrology or soil GHG emissions; thus, the fields were recategorized using principal component analysis according to their two-year mean water table (WT) level and soil volumetric water content. On average, fields with higher WT levels emitted significantly more CO₂ and N₂O, by 29% and 130% respectively, resulting in higher overall annual emissions (36,095 kg CO₂eq ha⁻¹ year⁻¹ versus 28,755 kg CO₂eq ha⁻¹ year⁻¹ in lower WT fields). High WT fields emitted more CO₂ in the spring and summer, and more N₂O in the fall and winter. Stepwise linear regressions showed that soil temperature was the main driver of soil CO₂ emissions, but drivers were unclear for N₂O and CH₄ emissions. The DNDC model overestimated the effect of freeze-thaw events on soil CO₂ emissions, and underestimated soil N₂O emissions, especially in the shoulder season. Annual soil N₂O emissions were poorly estimated by all three models, but the equation by Rochette et al. (2018) provided the most accurate estimate of mean annual soil N₂O emissions, underestimating them by 6% compared to 89% and 90% with the IPCC and DNDC models, respectively. The results indicate that lowering the WT could reduce soil emissions in blueberry crop rows; but more information on net field GHG budgets is needed before recommending drainage as a GHG mitigation practice for silt loam soils in Delta, British Columbia.
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Overwintering with plastic silage tarps as a tool to improve the climate resilience of organic vegetable production in British Columbia (2022)
Climate change is limiting the use of overwinter cover cropping in organic vegetable production and is driving the need for alternative cover options. Winter soil cover is important in protecting against nutrient leaching and erosion, both of which represent threats to the environment and economic costs to growers. This study investigated impacts of overwinter plastic tarping compared to cover cropping through a mother-daughter field trial in British Columbia. Research was conducted from 2019-2021 on 14 organic practicing vegetable farms, including two mother sites (University of British Columbia Farm and Green Fire Farm) and 12 daughter sites, in three agricultural regions (Lower Fraser Valley, Vancouver Island, and Kootenay Mountains). To determine the relationship between winter cover and crop nutrient sources, three approaches to spring nutrient amendment strategies and a control were trialed at the mother sites: (1) high compost, (2) low compost, (3) compost + fertilizer, and (4) control (no application). Plant available nitrogen (PAN), electrical conductivity (EC), and volumetric water content (VWC) were measured in the spring after tarp removal at all research sites. Additional measurements were taken at the mother sites, including PAN at the time of planting, mid-season, and post-harvest, and crop yield at the time of crop maturity. Spring PAN and EC increased under tarps relative to cover crops in all regions. Impacts to VWC varied between years and likely varies depending on the time of tarp removal. Data from UBC Farm indicate that tarps created lower VWC conditions over the winter until early spring (mid-March) after which time VWC under tarped conditions was higher than soil under cover crops. There were no consistent effects of the winter cover type on crop yields. Nutrient amendment strategies did not meaningfully interact with winter cover type with respect to spring PAN, EC, or VWC. In 2020, nutrient amendment strategy impacted post-harvest PAN at a 0-30 cm depth and crop yield at the mother sites. Results from this study help inform winter cover decisions for small-scale organic growers so that they may decrease the detrimental impacts to soil health from changing precipitation patterns caused by climate change.
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Assessing the impacts of agriculture on soil quality in a five-year crop-livestock rotation in the Fraser River delta, British Columbia (2021)
The Fraser River delta is one of the most intensively farmed agricultural regions of Canada. It is also an area of high ecological significance, providing habitat for migrating bird populations and aquatic species. To help provide habitat for bird populations, a five-year crop rotation has been developed for the Alaksen Wildlife Area. This rotation integrates perennial and annual crops and livestock production and could provide a promising alternative to intensive production in the region. A study of key soil quality indicators was conducted within the Alaksen to: i) compare key soil quality indicators to assess the impacts of land use type on soil quality, and ii) evaluate the effects of specific rotation practices (crop type, livestock) on key indicators to better understand the potential impacts of the five-year rotation on soil quality. In the fall of 2018, soil samples were taken from sixteen agricultural fields, three abandoned agricultural fields (old fields), and three relatively undisturbed forest patches and analyzed for soil organic carbon (SOC), bulk density (BD), pH and electrical conductivity (EC). Results showed that in the upper 15 cm depth agricultural and old fields, respectively, had 44% and 60% of the SOC as forest patches. Bulk density was 53% greater in agricultural fields than in old fields and 66% greater than forest in the upper 15 cm depth. There were no significant differences in soil indicators between annual and perennial crops fields, except for EC in annual crop fields, which was 52, 40 and 164% greater in the 0-15, 15-30, and 30-60 cm depth, respectively. Fields with livestock showed greater SOC and EC, and lower pH levels at some soil depths. Results of this study suggest that agriculture has negatively affected soil quality within Alaksen but these impacts varied with management. While including perennial crops in the rotation did not improve soil quality, including livestock offered some soil quality benefits, and merits further study based on its potential to improve soil quality in the region.
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Evaluating hedgerow and riparian buffer carbon storage potential in the Lower Fraser Valley from a field- and landscape-level perspective (2021)
Hedgerows and riparian buffers have been promoted for their potential to increase carbon storage capacity of agricultural landscapes. However, there has been little quantification of this potential. Using the Lower Fraser Valley of British Columbia as a case study, I contextualized differences in carbon observed in hedgerows and riparian buffers and compared soil organic carbon (SOC) across five land use and land cover categories. Three SOC metrics were used to evaluate the below-ground carbon storage potential of each land use and land cover category. At the landscape-level I designed remote sensing methods to extract hedgerows and riparian buffers from 5m resolution RapidEye imagery. I reapplied methods to imagery collected in previous years to assess recent changes (2009 - 2017) in hedgerow and riparian buffer coverage.Greater species richness in hedgerows was highly correlated with greater SOC across all metrics. When measuring SOC using a mass-based approach approximating a 30 cm depth, or 0.4 t m⁻² of soil equivalent, high-diversity hedgerows and woody riparian buffers had greater SOC mass than managed grasslands. However, no differences were observed between either high-diversity hedgerows or woody riparian buffers and agricultural production land cover categories when using a depth-based approach. Carefully calibrated spectral, textural, and geometric rules developed from high spatial resolution remotely sensed imagery delineated and classified hedgerows and riparian buffers with a combined accuracy of 68% (kappa 0.63). In 2017, hedgerows and riparian buffers in the Lower Fraser Valley totaled 78.0 and 40.6 km², respectively. Change detection was less accurate (kappa 0.35), estimating increases in combined hedgerow and riparian buffer coverage from 2009 to 2017 by 72.7 % relative to the 2009 coverage and 2.3 % relative to the study area. Adequate broad scale hedgerow and riparian buffer maps, despite difficulties in temporal change detection, are a critical first step towards modelling carbon storage potential at a regional level.
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Soil, crop yield, and cost trade-offs of organic nutrient management strategies across mixed vegetable farms in southwest British Columbia (2020)
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, organicnutrient 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 wereused. 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 andeconomic 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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Forage crop nitrogen recovery and nitrogen field-losses determined on semi-virtual dairy farms under integrated nutrient and crop management scenarios (2019)
In the Lower Fraser Valley region of BC, intense dairy production occupies a relatively small agricultural land base. Farm-generated manure is often applied to forage crops at a very high rate to deal with the large quantities produced by high animal density. Local farmers also purchase additional mineral fertilizer to maximize production and profitability, which together with manure has far exceeded the nutrient uptake capability of crops. Surplus nitrogen (N) will lead to N loss through nitrate leaching and nitrous oxide emission. The objectives of this study are to quantify and compare (1) the crop N removal and apparent recovery of total N applied (TNR); and (2) nitrous oxide emission and nitrate leaching intensity of four dairy farm management scenarios that incrementally introduce beneficial management practices (BMPs) and advanced production techniques. I compared these four scenarios for annual crop yield, crop N removal, and TNR of silage corn and tall fescue. I quantified the seasonal and annual N field-losses through nitrous oxide emission and potential nitrate leaching. Finally, I also examined how adjusting cropland allocation would affect total crop yield, crop N removal, TNR, and N field-loss for the four scenarios. Planting a relay crop removed more N from corn plots while producing a similar amount of feed as the conventional scenario and also reduced nitrate leaching and leaching intensity by 70 %. Reduced grass harvest frequency increased grass yield substantially. Nitrification inhibitor, DCD, and irrigation improved TNR of both corn and grass and also reduced nitrous oxide emission from grass plots in 2017 and corn plots in 2018. In the dual-crop forage production system of 50 % corn and 50 % grass, TNR increased significantly only when all available BMPs of this study were integrated. Total nitrate leaching intensity abated more than 50 % when the relay crop and reduced grass harvest frequency were implemented. Adding DCD and irrigation reduced annual total nitrous oxide emission intensity by 40 %. Allocating 10 % more land to grow corn increased total feed production, but had little impact on total nitrate leaching and nitrous oxide emission.
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The effects of 2- and 3-year grassland set-asides on plant available nitrogen and greenhouse gas emissions in Delta, British Columbia (2019)
Since 1993, the Grassland Set-Aside (GLSA) Stewardship Program has incentivized farmers in the western Fraser River delta, British Columbia, Canada to plant a grass-legume mixture on active cropland and leave it fallow for 1-4 years to improve soil quality and provide wildlife habitat. Benefits to wildlife are well documented, but not well understood for soil quality. Study objectives were to quantify the effects of 2- and 3-year GLSAs on plant available nitrogen (N), crop production, soil quality, and greenhouse gas emissions. A field experiment was established in 2017 on a productive and unproductive field with fertilizer treatments (0 and 80-kg N ha⁻¹) compared across GLSA treatments (i) AC – GLSA biomass removed and (ii) 2G – 2-year-old GLSA biomass was incorporated, and seeded with beans. In 2018, fertilizer treatments (0 and 100-kg N ha⁻¹) were compared across the same GLSA treatments and (iii) 3G –3-year-old GLSA biomass was incorporated, and seeded with potatoes. Active carbon (POXC) and aggregate stability (MWD) were measured 3 times per growing season, plant available nitrogen (PAN) was sampled every 2 weeks from May-September, and carbon dioxide, methane, and nitrous oxide were measured weekly from May-September and every 3 weeks from October-April. MWD increased in 2G and 3G in the year of incorporation relative to AC and POXC increased for 3G relative to AC and 2G. Average seasonal PAN did not differ across treatments but was higher earlier in the season for 2G. Bean yields were greater in 2G compared to AC in the productive field, but otherwise crop yields did not respond to GLSA. N content of bean crops did not differ between treatments, was higher for 3G compared to AC in the unproductive field. 2G increased carbon dioxide emissions in 2018, but 3G only increased emissions in the 2018 production season. Nitrous oxide emissions treatments were higher in 2G treatments across all seasons, but lower in 3G treatments in the 2018 production season. Results suggest 2- and 3-year GLSAs do not increase average PAN to subsequent crops, but increase PAN earlier in the season, and increase crop yield and quality depending on subsequent crops.
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Evaluating field margins for wild bee conservation at the farm- and landscape-scale in the Agricultural Land Reserve of Delta, British Columbia (2017)
Wild bees provide essential pollination service to both agricultural crops and wild flowering plant species. The decline of wild bee species has been associated with a number of different threats, primarily the loss of natural habitat. The Delta Farmland & Wildlife Trust (DF&WT), a non-profit conservation organization, incentivizes farmers to plant hedgerows consisting of native shrubs and trees on the edge of their production fields, mainly to create habitat for wildlife in the Agricultural Land Reserve (ALR) of Delta, British Columbia. In this study, the value of DF&WT’s planted hedgerows was evaluated as foraging habitat for wild bees at both the farm and landscape-scale. During the summers of 2015 and 2016, I surveyed bees and flowers in planted hedgerows, as well as the two other most dominant field margin habitats, remnant hedgerows and grass margins. The relationship between floral resources and bees, as well as bee-flower visitations was analyzed and compared among these three habitat types. These empirical data were then used to parameterize the Conefor model, to evaluate the network of field margin patches within the agricultural landscape for their relative importance in landscape connectivity for wild bees.Overall, wild bees collected from flowers and pan traps were significantly more abundant, species rich and diverse in grass margins compared to planted and remnant hedgerows. While the strongest relationship was found between floral abundance and bee abundance, it did not explain the differences between habitat types alone. Bee-flower visitation records revealed a preference for herbaceous species mostly found in grass margins while only few recommended plant species for hedgerow plantings were visited. The results indicate that grass margins could be a valuable alternative conservation approach or addition to woody hedgerows if properly planned and managed. Connectivity indices generated by Conefor identified four grass margin patches that most contributed to overall landscape connectivity for bees with different dispersal abilities. These results can be used to help improve field edge management and the spatial targeting of activities by the DF&WT to improve the conservation of wild bee species.
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Nitrogen dynamics following incorporation of 3-year old grassland set-asides in Delta, British Columbia (2017)
The Grassland Set-aside (GLSA) Stewardship Program has been utilized by farmers in the lower Fraser River delta, British Columbia (BC), Canada since 1993. Farmers seed fields in a grass-legume mixture and leave them fallow for up to four years providing feeding habitat for raptors while subsequently improving soil quality. While the wildlife benefits have been well documented, soil quality improvement and benefits to succeeding crops are not well understood. The objective of this research is to quantify the nitrogen benefits to crop production after incorporation of 3-year-old GLSA. A regional experiment was conducted over two years, utilizing production fields transitioning from GLSA, paired with continuously cropped fields (Control) with matching management. A controlled field experiment was also conducted on a single 3-year-old GLSA, comparing fertilizer types, rates and timing of incorporation. In each experiment, soils were sampled every 10-14 days for ammonium (NH4) and nitrate (NO3) while ion probes, installed near the rooting zone tracked plant available nitrogen (PAN) throughout the season. The results from the regional experiment were confounding, in 2015 showing GLSA supplied an additional 18 kg PAN ha-1 compared to Control but showing no PAN benefits in 2016. While the PAN supplied by the GSLA remained consistent each year, the amount supplied by Control in 2016 was relatively higher. In both years, PAN following GLSA peaked later in the season than the Control, likely due to immobilization of nitrogen facilitated by incorporation of biomass with a high carbon to nitrogen (C:N) ratio. Immobilization also delayed NH4 release in the controlled experiment for up to 21 days and NO3 56 days. The controlled experiment also highlighted the importance of fertilizer type to subsequent PAN, showing synthetic treatments consistently supplied more PAN than Organic. Results from this study suggest that 3-year-old GLSAs can potentially improve PAN to subsequent crops; however, benefits provided by GLSA in Delta are dependent on a number of factors which include the C:N ratios of biomass, timing between incorporation and crop planting, precipitation and temperatures, and fertilizer type, all of which impact the timing and quantity of PAN and thus its utility to subsequent crops.
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Soil amendments from urban residuals and their effect on crop productivity and and nutrient cycling (2017)
Urban residuals have been used in agriculture to decrease disposal costs, recycle nutrients, and prevent or counteract the degradation of soils linked to the intensification of agriculture. Technological advancements continue to produce novel residuals that can be used as soil amendments, with the potential to reduce or eliminate waste. This thesis entails two studies that examine the potential to utilize new urban residuals for food production. The objectives of the first study were to look at the potential benefits and impacts, on crop productivity and nutrient cycling, of using monopotassium phosphate (MKP) fertilizers, made using the co-products of biodiesel production. The treatments in this study include MKP-M, a purified form of MKP, MKP-C, a crude MKP from biodiesel production with glycerin and MKP-C2, similar to MKP-C but with double the glycerin. There were no differences in yields in the field trial. The greenhouse trial showed higher pepper yields using MKP-C and foliar MKP-M, and higher number of fruits with foliar MKP-M and a retail MKP. Soil analyses suggest that glycerin in certain amounts can inhibit nitrification and improve nitrogen (N) uptake. In the second study, a compost like material (HTI Compost) made in 24 hours was tested to better understand the effects unstable and immature compost could have on yield, nutrient cycling and greenhouse gas (GHG) emissions. The treatments were the HTI compost, UBC farm compost (typical municipal compost), a mix of the two composts, HTI compost + bloodmeal, and no amendment. The results show the HTI treatments had similar yields to the UBC farm compost for beets, but lower yields in spinach due to reduced or delayed germination. The HTI treatments delayed soil N availability and resulted in higher GHG emissions. Emissions of carbon dioxide and methane from the HTI treatments were high in the beginning of the season when the compost was decomposing, while nitrous oxide emissions were highest later on as decomposition rates declined. These results show promising benefits for using urban residuals as soil amendments, but the management of these amendments is crucial to avoid any negative impacts on crop productivity or the environment.
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Evaluating potential impacts of hedgerow and riparian buffer management options on habitat and carbon stocks within the Agricultural Land Reserve of the Lower Fraser Valley, British Columbia (2016)
Non-production perennial vegetation (NPPV) on farmland provides wildlife habitat and/or ecosystem services (ES). Increasing NPPV area could help reverse the simplification of agricultural landscapes by providing small but potentially important patches of habitat on the edges of farm fields as well as increase the multifunctionality of the landscape to meet concurrent agricultural production and environmental objectives. Conflicts among these objectives are currently a challenge for the rapidly urbanizing Lower Fraser Valley (LFV), the most intensive agricultural region of British Columbia.The objectives of this study were to 1. Characterize NPPV hedgerows; 2. Map the current distribution of NPPV and associated carbon stocks; 3. Better understand the drivers of NPPV distribution and identify areas at higher risk of conversion to agricultural production; 4. Model potential NPPV management options to identify those that maximize habitat and carbon storage while minimizing farm land loss.Cluster analysis of hedgerow field survey data distinguished three distinct types which differed in composition but not size: Planted Trees, Mixed Remnant and Invasives. Remote sensing analysis found NPPV on 33.2% of the study area’s farmland, of which 56.2% consisted of large, contiguous stands of trees. However, 0.98 – 1.86 MT of carbon (75.5% of all NPPV carbon) in these stands, is at high risk of conversion to agriculture given strong correlation between indicators of agricultural expansion (IAE) and removal of stands located on the highest quality farmland. Conversely Hedgerows and Riparian Buffers were found to have positive, synergistic correlations with IAE. Spatially-explicit normative scenarios were used to evaluate impacts of NPPV management options. The addition of the most extensive option, Hedgerows + Riparian Buffers (All), showed the greatest impact to landscape pattern and carbon with 36 % - 711% improvement in these measures. However, these improvements were at the highest farmland area cost. Hedgerows exhibited the greatest impact to landscape pattern with the least trade-off of production area but did not store as much carbon as other NPPV options. The analysis illustrated clear trade-offs between habitat, carbon storage and production, where no specific management option maximized all three and thus recommendations should depend on objectives of stakeholders.
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Assessment of current status and modeling of future capacity for land based food self-reliance in southwest British Columbia (2015)
There is growing awareness that climate change, economic instability, resource limitations and population growth are profoundly impacting the capacity of the contemporary global food system to meet human nutrition needs. Although there is widespread recognition that food systems must evolve in the face of these issues, a polarized debate has emerged around the merit of global-verses-local approaches to this evolution. Local food system advocates argue that increasing food self-reliance will concomitantly benefit human health, the environment, and local economies, while critics argue that only a globalized system will produce enough calories to efficiently and economically feed the world. This debate largely takes place in absence of knowledge of the current food self-reliance status of specific regions and capacity to increase it in the future. This study addressed this knowledge gap by developing methods to assess current (2011) status and model future (2050) capacity for land based food self-reliance in a diet satisfying nutritional recommendations and food preferences that accounts for seasonality of crop production, and comparing self-reliance in livestock raised with and without locally produced feedstocks. The methods were applied to the southwest British Columbia bio-region (SWBC). Results indicated that SWBC production of feed and food grain is a major constraint on self-reliance. Total dietary self-reliance of SWBC was 12% in 2011 if discounting livestock feed imports or 40% if including them. Self-reliance could be increased in 2050 in a Localized food system in which crops are allocated to agricultural lands in a manner that maximizes food self-reliance, but not in a Business as Usual (BAU) food system in which crop and livestock production follows 2011 patterns. The average of nine modeled scenarios for 2050 food self-reliance in the Localized food system was 26% if discounting livestock feed imports or 44% if including livestock raised with imported feed, and in the BAU food system was 8% and 23% respectively. Analysis revealed that both food systems are more sensitive to changes in farmland availability than climate change-induced changes in crop yield. Land use results indicate that horticultural crop production would dominate farmland use in a scenario of increased food self-reliance.
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Evaluating farm hedgerows for their climate change mitigation potential in the lower Fraser River delta of British Columbia (2015)
Hedgerows have potential to help mitigate greenhouse gas emissions from agricultural activities by sequestrating carbon in woody biomass and in soil. In the Fraser Valley of British Columbia, a hedgerow stewardship program supports farmers to plant hedgerows to create habitat for biodiversity conservation and to improve ecosystem services, but it is unclear how much hedgerows contribute to climate change mitigation. This study evaluated components of the mitigation potential of two types of hedgerows, those planted by the stewardship program, and those that are remnant in the region. We quantified the carbon stored in woody biomass and soil, and greenhouse gas emissions of these two hedgerow types relative to neighbouring production fields used for cultivation of annual crops. There was no significant difference in the biomass carbon in the two hedgerow types despite age differences. Woody vegetation species diversity was significantly greater in planted hedgerows than remnant hedgerows for richness, Shannon, and Simpson measures. Planted hedgerows stored greater soil carbon than remnant hedgerows to 1.2 t m-² standard soil mass. Soil carbon was significantly correlated with the Shannon, and Simpson diversity of the hedgerow shrubs and trees indicating that planting a diversity of woody species likely has a positive effect on the mitigation potential of hedgerows on farmland.Carbon dioxide, nitrous oxide, and methane effluxes from soil, measured bi-monthly for one year indicate that the mitigation potential is not straightforward. For the 6-month production and non-production seasons, carbon dioxide was significantly greater in hedgerows than production fields. Relative emissions, emissions from hedgerows relative to their neighbouring production fields, from planted hedgerows were significantly greater than remnant hedgerows. For the 6-month production season, nitrous oxide emissions were significantly lower in hedgerows than productions fields, while no difference were observed in the non-production season or between hedgerow types. No significant differences were observed between seasons or hedgerow types for methane fluxes. These findings suggest that planting hedgerows may be an important management option to store carbon on agricultural land in the Fraser River delta relative to remnant hedgerows, but their net impact on climate change mitigation is still unclear.
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Nutrient Management Effects on Soil Quality, Microbial Community Composition, and Nitrogen Cycling in Tall Fescue Forage Grass Production Systems (2015)
In the Fraser Valley of southwest BC, dairy production is an important industry but large numbers of dairy cows present challenges for manure management. Dairy manure is a valuable source of plant nutrients, yet surplus application may lead to N loss through NO₃- leaching and N₂O emissions. Removing solids from whole dairy manure reduces the organic N and C contents, potentially improving crop N uptake, but reducing soil microbial activity compared to whole manure. The objective of this study was to quantify long term effects of contrasting nutrient applications to perennial grass on soil microbial activity and community structure, and to test relationships with soil properties and rates of N transformation. Microbial community structure and activity (biomass, phospholipid fatty acid biomarkers, hydrolyzing enzyme activities) and N dynamics (net mineralization and nitrification, lysimeter leachate NO₃-, N₂O emissions) were measured in 2013 and 2014 on a stand of tall fescue (Fetusca arundinacea Schreb.) established in 2002 at Agassiz, BC, on soils receiving: whole dairy slurry manure, separated liquid fraction, NH₄NO₃ fertilizer, or alternating manure-fertilizer (all applied at 400 kg N/ha/yr equivalent) four times per year. In the autumn of 2013, the nitirifcation inhibitor, Nitrapyrin®, was applied to sub-plots of each treatment to assess its potential to minimize N losses from nutrient amendments.Soil in plots receiving whole or liquid manure had higher microbial biomass than plots receiving commercial fertilizer or unamended plots, and higher activity of cellulose-degrading enzymes than plots receiving no amendment. Both microbial biomass and cellobiosidase activity (cellulose-degrading enzyme) were positively correlated with total soil C, N, and P. Fungal:bacterial ratios were higher in control and whole manure than fertilizer and liquid treatments. Emissions of N₂O and concentrations of NO₃- in leachate were consistently positively correlated with abundance of bacterial biomarkers, but not total microbial biomass. N mineralization and nitrification were not correlated with any microbial group, but were positively correlated with NO₃- in leachate. The nitrification inhibitor Nitrapyrin® had no significant impact on soil inorganic N concentrations, N mineralization or nitrification, or N₂O emissions, however it increased soil microbial biomass and changed community structure and surprisingly increased NO₃- leachate.
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Publications
- Environmental phosphorus risk classes for silage corn in the Fraser Valley, Canada (2025)
Agriculture Ecosystems and Environment, 381 - 25-years of stewardship programs enhance regenerative outcomes in river delta soils of southwestern British Columbia, Canada (2024)
Geoderma, 443 - Filling the gaps in soil data: A multi-model framework for addressing data gaps using pedotransfer functions and machine-learning with uncertainty estimates to estimate bulk density (2024)
Catena, 245 - Mineral phosphorus fertilization for silage corn in manured soils in the Fraser Valley, Canada (2024)
Agronomy Journal, 116 (1), 362-379 - The carbon balance and water use efficiency of an intensively managed forage crop in the Lower Fraser Valley in British Columbia, Canada (2024)
Agricultural and Forest Meteorology, 357 - A framework for recalibrating pedotransfer functions using nonlinear least squares and estimating uncertainty using quantile regression (2023)
Geoderma, 439 - Estimating Net Carbon and Greenhouse Gas Balances of Potato and Pea Crops on a Conventional Farm in Western Canada (2023)
Journal of Geophysical Research Biogeosciences, 128 (3) - Effects of increasing soil pH to near-neutral using lime on phosphorus saturation index and water-extractable phosphorus (2022)
Canadian Journal of Soil Science, 102 (4), 929-945 - Evaluating hedgerows for wild bee conservation in intensively managed agricultural landscapes (2022)
Agriculture Ecosystems and Environment, 326 - Nitrous oxide emissions from productive and degraded potato fields in the Fraser Valley delta of British Columbia (2022)
Canadian Journal of Soil Science, 102 (4), 1000-1004 - Soil priorities in British Columbia, Canada (2022)
Geoderma Regional, 29 - Trade-offs in organic nutrient management strategies across mixed vegetable farms in Southwest British Columbia (2022)
Frontiers in Sustainable Food Systems, 6 - Woody perennial polycultures in the U.S. Midwest enhance biodiversity and ecosystem functions (2022)
Ecosphere, 13 (1) - Agroecosystem Health and Services (2021)
Introduction to Agroecology, 69-84 - Assessing the Circularity of Nutrient Flows Across Nested Scales for Four Food System Scenarios in the Okanagan Bioregion, BC Canada (2021)
Frontiers in Sustainable Food Systems, 5 - Assessing the circularity of nutrient flows related to the food system in the Okanagan bioregion, BC Canada. (2021)
Resources Conservation and Recycling, 174 - Characterization of shortwave and longwave properties of several plastic film mulches and their impact on the surface energy balance and soil temperature (2021)
Solar Energy, 214, 457-470 - Global Climate Change and Agriculture (2021)
Introduction to Agroecology, 119-135 - Integrated crop-livestock systems: A sustainable land-use alternative for food production in the Brazilian Cerrado and Amazon (2021)
Journal of Cleaner Production, 283 - Integrated farm management systems to improve nutrient management using semi-virtual Farmlets: Agronomic responses (2021)
Environmental Research Communications, 3 (7) - Soils as the Basis for Cultivated Ecosystems (2021)
Introduction to Agroecology, 33-48 - Substituting vetch and chicory for rye in a cover crop mixture enhanced nutrient release (2021)
Canadian Journal of Soil Science, 101 (2), 339-343 - Towards a circular nutrient economy. A novel way to analyze the circularity of nutrient flows in food systems (2021)
Resources Conservation and Recycling, 172 - A novel methodology to characterize and quantify regional farmscape non-production perennial vegetation carbon storage and potential for loss in Southwest British Columbia (2020)
Agroforestry Systems, 94 (5), 1947-1958 - Greenhouse gas exchange over a conventionally managed highbush blueberry field in the Lower Fraser Valley in British Columbia, Canada (2020)
Agricultural and Forest Meteorology, 295 - Labile soil carbon fractions as indicators of soil quality improvement under short-term grassland set-aside (2020)
Soil Research, 58 (4), 364-370 - Mapping soil organic carbon and clay using remote sensing to predict soil workability for enhanced climate change adaptation (2020)
Geoderma, 363 - Nitrogen dynamics following incorporation of 3-year old grassland set-asides in the fraser river delta of british columbia (2020)
Agronomy, 10 (9) - Perennial Staple Crops: Yields, Distribution, and Nutrition in the Global Food System (2020)
Frontiers in Sustainable Food Systems, 4 - Tracking changes in soil organic carbon across the heterogeneous agricultural landscape of the Lower Fraser Valley of British Columbia (2020)
Science of the Total Environment, 732 - Evaluating ecosystem service trade-offs and synergies from slash-and-mulch agroforestry systems in El Salvador (2019)
Ecological Indicators, 105, 264-278 - Evaluating sampling efforts of standard laboratory analysis and mid-infrared spectroscopy for cost effective digital soil mapping at field scale (2019)
Geoderma, 356 - Greater nitrogen availability, nitrous oxide emissions, and vegetable yields with fall-applied chicken relative to horse manure (2019)
Agronomy, 9 (8) - PARTICIPATORY EVALUATION of IMPROVED GRASSES and FORAGE LEGUMES for SMALLHOLDER LIVESTOCK PRODUCTION in CENTRAL AMERICA (2019)
Experimental Agriculture, 55 (5), 776-792 - Plant Species Composition and Forage Production 14 Yr After Biosolids Application and Grazing Exclusion (2019)
Rangeland Ecology and Management, 72 (6), 996-1004 - Quantifying trade-offs among on-farm and off-farm fertility sources to make vegetable organic farming systems more sustainable (2019)
Agriculture Ecosystems and Environment, 286 - Short-term effects of grassland set-asides on soil properties in the fraser river delta of British Columbia (2019)
Canadian Journal of Soil Science, 99 (2), 136-145 - Towards multifunctional land use in an agricultural landscape: A trade-off and synergy analysis in the Lower Fraser Valley, Canada (2019)
Landscape and Urban Planning, 184, 88-100 - Using agroecology to stimulate the greening of agriculture in China: a reflection on 15 years of teaching and curriculum development (2019)
International Journal of Agricultural Sustainability, 17 (4), 298-311 - Corrigendum:: Cultivating climate resilience: A participatory assessment of organic and conventional rice systems in the Philippines (Renewable Agriculture and Food Systems (2018) 33:3 (225–237) DOI: 10.1017/S1742170517000709) (2018)
Renewable Agriculture and Food Systems, 33 (5), 496 - Cultivating climate resilience: A participatory assessment of organic and conventional rice systems in the Philippines (2018)
Renewable Agriculture and Food Systems, 33 (3), 225-237 - Greater impacts of incubation temperature and moisture on carbon and nitrogen cycling in poultry relative to horse manure-based soil amendments (2018)
Journal of Environmental Quality, 47 (4), 914-921 - Improving the utility of erosion pins: absolute value of pin height change as an indicator of relative erosion (2018)
Catena, 163, 427-432 - Native bacterial communities and listeria monocytogenes survival in soils collected from the lower mainland of British Columbia, Canada (2018)
Canadian Journal of Microbiology, 64 (10), 695-705 - One-time application of biosolids to ungrazed semiarid rangelands: 14 yr soil responses (2018)
Canadian Journal of Soil Science, 98 (4), 696-708 - Protection from wintertime rainfall reduces nutrient losses and greenhouse gas emissions during the decomposition of poultry and horse manure-based amendments (2018)
Journal of the Air and Waste Management Association, 68 (4), 377-388 - A novel methodology to assess land-based food self-reliance in the Southwest British Columbia bioregion (2017)
Renewable Agriculture and Food Systems, 32 (2), 112-130 - Application of biochar and nitrogen influences fluxes of CO2, CH4 and N2O in a forest soil (2017)
Journal of Environmental Management, 192, 203-214 - Comparison of selected soil properties following grassland set-aside and annual crop rotations in the fraser river delta of British Columbia (2017)
Canadian Journal of Soil Science, 97 (4), 783-788 - Disintegration of compostable foodware and packaging and its effect on microbial activity and community composition in municipal composting (2017)
International Biodeterioration and Biodegradation, 125, 157-165 - Long-term alternative dairy manure management approaches enhance microbial biomass and activity in perennial forage grass (2017)
Biology and Fertility of Soils, 53 (6), 613-626 - Predicting carbon benefits from climate-smart agriculture: High-resolution carbon mapping and uncertainty assessment in El Salvador (2017)
Journal of Environmental Management, 202, 287-298 - Soil CO2, CH4 and N2O emissions from production fields with planted and remnant hedgerows in the Fraser River Delta of British Columbia (2017)
Agroforestry Systems, 91 (6), 1139-1156 - Determining greenhouse gas emissions and removals associated with land-use and land-cover change (2016)
Methods for Measuring Greenhouse Gas Balances and Evaluating Mitigation Options in Smallholder Agriculture, 37-70 - Comparison of CO2, CH4 and N2O soil-atmosphere exchange measured in static chambers with cavity ring-down spectroscopy and gas chromatography (2015)
Agricultural and Forest Meteorology, 211-212, 48-57 - Using hedgerow biodiversity to enhance the carbon storage of farmland in the Fraser River delta of British Columbia (2015)
Journal of Soil and Water Conservation, 70 (4), 247-256 - Climate-Smart Landscapes: Opportunities and Challenges for Integrating Adaptation and Mitigation in Tropical Agriculture (2014)
Conservation Letters, 7 (2), 77-90 - Ecosystem services in agricultural landscapes (2013)
Integrating Ecology and Poverty Reduction Ecological Dimensions, 17-51 - Linking biodiversity and nutrition: Research methodologies (2013)
Diversifying Food and Diets Using Agricultural Biodiversity to Improve Nutrition and Health, 9780203127261, 140-163 - Assessment of best management practices for nutrient cycling: A case study on an organic farm in a Mediterranean-type climate (2012)
Journal of Soil and Water Conservation, 67 (1), 16-31 - Effective monitoring of agriculture: A response (2012)
Journal of Environmental Monitoring, 14 (3), 738-742 - Social-ecological and regional adaptation of agrobiodiversity management across a global set of research regions (2012)
Global Environmental Change, 22 (3), 623-639 - Community essay tools for enhancing interdisciplinary communication (2011)
Sustainability Science Practice and Policy, 7 (1), 74-80 - Biodiversity and multiple ecosystem functions in an organic farmscape (2010)
Agriculture Ecosystems and Environment, 139 (1-2), 80-97 - Identifying potential synergies and trade-offs for meeting food security and climate change objectives in sub-Saharan Africa (2010)
Proceedings of the National Academy of Sciences of the United States of America, 107 (46), 19661-19666 - Monitoring the world's agriculture (2010)
Nature, 466 (7306), 558-560 - Factors affecting adoption of hedgerows and other biodiversity-enhancing features on farms in California, USA (2009)
Agroforestry Systems, 76 (1), 195-206 - Growth, nutrition, and soil respiration of a mycorrhiza-defective tomato mutant and its mycorrhizal wild-type progenitor (2008)
Functional Plant Biology, 35 (3), 228-235 - Nematode diversity, food web condition, and chemical and physical properties in different soil habitats of an organic farm (2008)
Biology and Fertility of Soils, 44 (5), 727-744 - Transition to large-scale organic vegetable production in the Salinas Valley, California (2008)
Agriculture Ecosystems and Environment, 126 (3-4), 168-188
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