Sean Smukler

Associate Professor

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Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2021)
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
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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 (2010 - 2020)
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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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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