Agricultural Soils In Canada Research Articles

Reactive nitrogen losses from Canadian agricultural soils over 36 years

Agriculture is a major source of reactive nitrogen (Nr) losses through ammonia (NH3) volatilization, nitrous oxide (N2O) emissions and nitrate (NO3−) leaching. A Canadian Agricultural Nitrogen Budget for Reactive N (CANBNr) model was developed to estimate the nitrogen (N) balance in soils, including N removals by harvested crops and Nr losses for the years 1981–2016 across Canada. Annual N inputs to farmland include commercial fertilizer N, livestock manure N, symbiotic and asymbiotic biological N fixation and atmospheric N deposition of NOx and NH3. The total annual N input for Canadian farmland was 5528 Gg N (103.2 kg N ha−1) in 2016 where N removal by crops and Nr accounted for 72.5 % (74.9 kg N ha−1) and 13.4 % (13.9 kg N ha−1), respectively. The Nr losses from N2O emissions, NH3 volatilization and NO3− leaching accounted for 64 Gg N (1.2 kg N ha−1), 330 Gg N (6.2 kg N ha−1) and 348 Gg N (6.5 kg N ha−1), which represents between1.2–6.3 % of total N input. A total of 777 Gg N (14.5 kg N ha−1) remained in the soil as surplus N (14.1 % of total N input), which could be available to subsequent crops in dryer regions but might be subject to N2O loss through nitrification or denitrification processes or NO3− leaching following heavy rains in humid regions. Nitrous oxide and ammonia emissions increased over a 36-year period due to increased fertilizer N inputs. The percentage of N inputs that was estimated to be lost as Nr increased from 17.9 % in 1981 to the peak level of 19.8 % in 2001 and then declined to 13.4 % in 2016. Total N removal by crops increased at a greater rate than N input during the 2001–2016 period resulting in an increased N uptake by crops over the last 15 years. The improved management of fertilizer N for agricultural systems represents a key opportunity for both farmers and policy makers to further reduce Nr losses from Canadian farmland without negatively impacting productivity.

Identification and genomic characterization of Pseudomonas spp. displaying biocontrol activity against Sclerotinia sclerotiorum in lettuce.

Lettuce is an economically major leafy vegetable that is affected by numerous diseases. One of the most devastating diseases of lettuce is white mold caused by Sclerotinia sclerotiorum. Control methods for this fungus are limited due to the development of genetic resistance to commonly used fungicides, the large number of hosts and the long-term survival of sclerotia in soil. To elaborate a new and more sustainable approach to contain this pathogen, 1,210 Pseudomonas strains previously isolated from agricultural soils in Canada were screened for their antagonistic activity against S. sclerotiorum. Nine Pseudomonas strains showed strong in vitro inhibition in dual-culture confrontational assays. Whole genome sequencing of these strains revealed their affiliation with four phylogenomic subgroups within the Pseudomonas fluorescens group, namely Pseudomonas corrugata, Pseudomonas asplenii, Pseudomonas mandelii, and Pseudomonas protegens. The antagonistic strains harbor several genes and gene clusters involved in the production of secondary metabolites, including mycin-type and peptin-type lipopeptides, and antibiotics such as brabantamide, which may be involved in the inhibitory activity observed against S. sclerotiorum. Three strains also demonstrated significant in planta biocontrol abilities against the pathogen when either inoculated on lettuce leaves or in the growing substrate of lettuce plants grown in pots. They however did not impact S. sclerotiorum populations in the rhizosphere, suggesting that they protect lettuce plants by altering the fitness and the virulence of the pathogen rather than by directly impeding its growth. These results mark a step forward in the development of biocontrol products against S. sclerotiorum.

Long-term retention of carbon from litter decay in diverse agricultural soils in Canada and New Zealand

Identifying the primary regulators of plant litter decay in agricultural soils is important for understanding ecosystem function now and for managing post-harvest litter in a warmer world. We conducted a litter decay study at 11 sites in Canada and New Zealand with diverse soils and climates. We incorporated 13C-labelled barley litter into the surface 10 cm of soil and monitored amount remaining over 8–10 years; at five sites litter was also applied to the soil surface to simulate no-tillage. Our objectives were to evaluate litter decay as influenced by soil type, tillage practice, and environmental conditions, and quantify the most important factors controlling C retention in soil. Loss of C via decomposition occurred quickly – more than half was lost within 1 year and only about 5–12% remained at the end of the experiment. A double exponential decay model, based on temperature and developed from the first 5 years of the study, accurately described litter decay, but only after re-tuning using measurements from the full experimental period. Including precipitation in the model further improved its fit. Soil properties exerted minimal discernible influence on the amount of litter C remaining, implying that properties such as the amount and surface area of clay minerals, were less important than climate in limiting litter decay or enhancing retention of C in soil. Comparison of litter application treatments showed that no-till slowed decay of plant litter, but only for a short time (∼1 yr) and only in environments with a mean annual precipitation of <1000 mm. These findings have implications for the role of soils in climate mitigation. If only 10% of added plant litter C remains in soil beyond a few years, regardless of climate, residue placement, or soil type, then rates of soil gain are limited without substantive increases in residue inputs.

Change in soil organic carbon storage as influenced by forestland and grassland conversion to cropland in Canada

Conversion of native grassland and forest to agricultural land results in significant losses of soil organic carbon (SOC). However, the quantity of SOC loss upon conversion of native grassland and forest varies with climate, soil texture and agricultural management practices. In this study, we quantified the change of SOC stock as influenced by native grassland and forest conversion to agricultural soils in Canada through a meta-analysis. We determined both the absolute and relative change of SOC from its native state upon the conversion to agriculture. In more humid and temperate region of Eastern Canada losses of SOC upon the conversion of forest to agricultural land varied with soil textures, on an absolute basis, 18 t C ha−1 for the coarse-textured soil, 43 t C ha−1 for the medium-textured soil, and 65 t C ha−1 for the fine-textured soil from its native vegetation; corresponding, on a relative basis, to 22%, 30% and 32%, respectively. On the Canadian prairies, forestland conversion to cropland resulted in losses of 27 t C ha−1 or 25% for the medium-textured soil whereas there was no change in SOC for the coarse-textured soil. On the Canadian prairies, the conversion of native grassland to agriculture resulted in losses of SOC, on average from 15, 26, and 5 t C ha−1 in coarse-, medium- and fine-textured soils, respectively. However, because of high inherent variation in SOC stocks among the various soil textures, losses of SOC upon grassland conversion, on a relative basis, were highly variable (14–26%), and no statistically significant differences were observed among soil texture classes. The results of this work clearly show that climate and soil texture are main drivers of SOC change after the conversion of native grassland and forest to agriculture and are key factors that must be considered in the development of either national or regional SOC models. The results of this study suggest that more detailed stratification of samples across soil textures and climates improve the accuracy of estimates of SOC loss associated with native grassland and forest conversion to agriculture.

Simulating nitrogen balance in Canadian agricultural soils from 1981 to 2016

Agriculture produces food, fiber and biofuels for the world's growing population, however, agriculture can be a major contributor of nitrogen (N) losses including emissions of ammonia (NH3), nitrous oxide (N2O) and nitrate (NO3−) leaching and runoff. A Canadian Agricultural Nitrogen Budget for Reactive N (CANBNr) model was developed to estimate the soil N balance in 3487 soil landscape of Canada polygons from 1981 to 2016. The CANBNr model integrates NH3 emission from fertilizers, manure from housing, storage and field, as well as direct/indirect N2O emissions from fertilizers, manures, crop residues and soil organic matter. The NO3− leaching is estimated based on the residual soil N (RSN) at harvest and drainage derived with the DeNitrification-DeComposition (DNDC) model. From 1981 to 2016, the N input from fertilizer and N fixation increased at a greater rate than N removal in harvested crops in all provinces of Canada, resulting in an increase in the RSN and N losses. In 2016, the Prairie provinces had lower N losses (11.7 kg N ha−1) from N2O, NH3 and NO3− compared with 43.2 kg N ha−1 in central Canada, and 76.5 kg N ha−1 in Atlantic Canada. However, the Prairie provinces had 84.3% of the total Canadian farmland (74.3% of the total Canadian N input), while central Canada had 12.9% of Canadian farmland (21.7% of the total Canadian N input). In the Prairie provinces, the total N2O loss from fertilizer N ranged 4.4–8.6 Gg N whereas NH3 loss ranged from 17.1 to 44.6 Gg N and these values were influenced by both emission intensity and total land area. Total N2O losses from manure were highest in Alberta, Ontario and Quebec resulting in 4.8, 4.4, and 3.4 Gg N and NH3 losses from manure were also highest in these 3 provinces at 61.1, 45.2 and 40.4 Gg N, respectively. Nitrate leaching was impacted by drainage volumes, soil type and N inputs. In the non-growing season, NO3− leaching losses (36-yr average) were 63.3 Gg in Ontario and 57.5 Gg N in Quebec compared with 20.8 Gg N for Ontario and 35.5 Gg N for Quebec in the growing season. In contrast, the Prairie provinces showed higher NO3− leaching in the growing season (23.1–37.4 Gg N) than in the non-growing season (10.4–13.7 Gg N). In summary, total fertilizer N increased the most over the 36 years in the Prairies which resulted in increased RSN and N leaching losses that will require further intervention.

Ratio of non-growing season to growing season N2O emissions in Canadian croplands: an update to national inventory methodology

National inventory reporting of agricultural nitrous oxide (N2O) emissions in Canada is based primarily on measurements obtained using static chambers. In regions with cold winters and an accumulated snowpack (including Canada), these measurements tend to focus on the growing season (typically May–October). However, research has shown that emissions continue throughout the non-growing season (NGS) and that these account for a significant proportion of annual emissions. In the Canadian National Inventory NGS emissions currently are assumed to be adequately captured in western Canada, while they are accounted for in eastern Canada by multiplying the growing season emissions by a correction factor of 1.4, a value that was derived based on a limited number of measurements. Here we use recent Canadian studies to validate this correction factor. We collected data from available Canadian studies that measured soil N2O emissions from agricultural systems for the entire year and determined the proportion of these emissions that occurred during the NGS. The proportion of annual N2O emissions that occurred during the NGS varied widely, ranging from −4% to 119% with a mean of 35.5%, compared to the previous estimate of 30%. Due to high variability, few differences were observed between means associated with climatic, soil, and management variables. To correct for NGS N2O emissions from Canadian agricultural soils, we suggest that the current correction factor for converting growing season to total annual emissions be changed from 1.4 to 1.55 and that this be used for all agricultural soils in Canada rather than just eastern Canada.

A parsimonious water budget model for Canadian agricultural conditions

Study regionThis study used data collected from three cropland sites (two in Manitoba and one in Prince Edward Island) in Canada. Study focusIn efforts to accurately describe the water dynamics in agricultural soils, most of the agri-hydrological models developed are highly complex, such that they require detailed input data, of which most of them are not always measured or otherwise readily available. However, the comprehensive and complex representations of the processes may not be justified when data is scarce. Thus, this study developed a soil water budget model that could describe the movement of water through Canadian agricultural soils using a few parameters only. The model was developed by selecting algorithms from various existing models, whose data requirements are readily available in literature and public Canadian databases. New hydrological insightsThe model developed in this study can simulate evapotranspiration, runoff, deep percolation, and soil moisture content for various seasons (i.e., growing, non-growing/dormant, and pre-planting/post-harvest) with minimum data requirement, which addresses the limited availability of data in the country for crop and hydrological modeling. Moreover, the model is simple and easy to use, and can work without calibration. It was tested using three site-specific datasets, and results show that despite its simplicity, its overall performance was comparable with those of other agricultural models that use cascade flow framework for hydrology.

Developing a country specific method for estimating nitrous oxide emissions from agricultural soils in Canada

Accurate estimates of nitrous oxide (N2O) emissions from agricultural soils and management factors that influence emissions are necessary to capture the impact of mitigation measures and carry out life cycle analyses aimed at identifying best practices to reduce greenhouse gas emissions. We propose improvements to a country specific method for estimating N2O emissions from agricultural soils in Canada based on a compilation of soil N2O flux data from recent published literature. We provide a framework for the development of empirical models that could be applied in regions where similar data and information on N2O emissions are available. The method considers spatial elements such as soil texture, topography and climate based on a quantitative empirical relationship between synthetic N-induced soil N2O emission factor (EF) and growing season precipitation (P) {N2OEF = e(0.00558P−7.7)}. Emission factors vary from less than 0.0025 kg N2O-N kg N−1 in semi-arid regions of Canada to greater than 0.025 kg N2O-N kg N−1 in humid regions. This approach differentiates soil N2O EFs based on management factors. Specifically, empirical ratio factors are applied for sources of N of 1.0, 0.84, and 0.28 for synthetic N, animal manure N and crop residue N, respectively. Crop type ratio factors where soil N2O EFs from applied manure- and synthetic-N on perennial crops are approximately 19% of those on annual crops. This proposed approach improves the accuracy of the dominant factors that modulate N2O emissions from N application to soils.

Revisiting no-till’s impact on soil organic carbon storage in Canada

Accurate estimates of soil organic carbon (SOC) stock change as influenced by tillage practices are prerequisites to quantify the impact of mitigation measures on greenhouse gas emissions associated with crop production. In this study, we compiled SOC stock change data as influenced by tillage practices, i.e. no-till (NT) versus conventional tillage (CT), on agricultural soils in Canada. We determined the rate of C change as a function of soil texture and climate stratified by time since the management change. In the cool and humid climates of Eastern Canada, the impacts of NT were inconsistent and resulted in a decline in C storage rate in the years shortly following management change, but SOC recovered over time. Carbon losses were particularly high on fine and coarse textured soils, whereas in medium textured soils NT tended to increase SOC. On the Canadian prairies NT consistently increased SOC. The rate of gain in SOC under NT decreased over time with higher rates in the 3−10 years following a change to NT at a rate of 740 kg C ha−1 yr−1 or 1.3 % yr−1. Rates declined to 260 kg C ha−1 yr−1 or 0.87 % yr−1 for periods from 11–20 years after tillage change, and to 95 kg C ha-1 yr−1 or 0.23 % for periods longer than 20 years. The results of this work clearly show climate, soil texture and duration of management as main drivers of SOC change under NT in Canada and key factors that must be considered in the development of either national or regional SOC models. The results of this study suggest that more detailed stratification of soil texture, climate and duration of NT adoption is required for more accurate estimates of SOC storage rates associated with NT for Canada.

Phosphorus accumulation in Canadian agricultural soils over 30 yr

Phosphorus (P) loss to freshwater is a key driver of eutrophication, and understanding the scale and spatial distribution of potential P sources is a key pre-requisite for implementing policies for P management to minimize environmental impacts. Soil test P (STP) is a useful indicator of the accumulation of P in soils, but these data are not readily available for most agricultural land in Canada, so the cumulative P balance (P inputs as manure or fertilizer minus removal of P in crops) is calculated as a proxy for this value. Cumulative P balance is an important calculation within the indicator of risk of water contamination by P, so allocations of manure and fertilizer P to cropland were updated within the calculation of P balance, and for Ontario, data from 1961 to 1980 were added to account for P applications during that period. The STP concentrations were calculated from the resulting cumulative P balances. When compared with reported STP concentrations, the predicted concentrations showed a statistically significant regression at the national (R2 = 78%) and provincial scale (Ontario, R2 = 36%; Prince Edward Island, R2 = 36%; Manitoba, R2 = 72%; British Columbia, R2 = 40%). There was significant variation in the cumulative P balance across Canada, with the highest values corresponding with areas of high livestock density, whereas large zones of P deficit were detected across the Prairies.

Addressing Imbalances in Phosphorus Accumulation in Canadian Agricultural Soils

Adequate phosphorus (P) is needed for crop production, but excessive P poses a potential risk to water quality. Results from the cumulative P balance calculations within the indicator of risk of water contamination by phosphorus (IROWC-P) developed in Canada were assessed to determine the spatial and temporal trends in P accumulation at a regional scale and to consider the implications of these trends. Regional cumulative P balances were calculated from census data as a proxy for soil test P (STP) values, including the contribution of fertilizer or manure P to these balances. Ideally, over time we would see a convergence of soil test values at the low end of the critical response range for crop growth, where agronomic and environmental considerations are balanced, but this does not appear to be the case for many regions in Canada. Nationally, about 61% of agricultural land was predicted to be low in STP, and over half of this land is failing to replace the P that is removed each year. While only about 10% of the agricultural land has accumulated significantly more P than is needed for crop growth, almost all of this land is continuing to accumulate P rather than drawing it down. Manure is the dominant P source for continuing accumulation in regions with high or very high estimated STP; reducing this input will be difficult because of the nature of manure and the investment in buildings and infrastructure tied to specific locations, but it is clear that current Canadian policies need strengthened.

Infrared spectroscopy estimation methods for water-dissolved carbon and amino sugars in diverse Canadian agricultural soils

Infrared spectroscopy has the potential to rapidly analyse soil water-dissolved carbon and amino sugars. In this study, mid-infrared (MIR) and near-infrared (NIR) spectra collected from soil water extracts or from bulk soils were analysed with partial least squares regression (PLSr) to estimate the concentrations of water-dissolved carbon and amino sugars in diverse agricultural soils collected from five field sites in two western and two eastern Canadian provinces. The MIR-PLSr models developed from soil water extract spectra estimated hot-water (100 °C) dissolved carbon (HWDC) [R2 = 0.97–0.70, ratio of prediction to deviation (RPDp) = 6.13–1.83] well, but the MIR-PLSr models did not estimate cold-water (21 °C) dissolved carbon (CWDC) well (R2 = 0.82–0.50, RPDp = 2.35–1.42). The model estimates of HWDC at the multisite scale (all samples together) and for the two western Canada sites (R2 = 0.97–0.93, RPDp = 6.13–3.68) surpass the modal estimates for the three eastern Canadian sites (R2 = 0.81–0.70, RPDp = 2.28–1.83). The MIR- and NIR-PLSr models derived from bulk soil spectra both estimated HWDC well at the multisite scale (R2 = 0.91–0.88, RPDp = 3.32–2.90) and for the western Canada sites (R2 = 0.90–0.87, RPDp = 3.18–2.96). Models developed from hot-water extract spectra and bulk soil spectra resulted in poor estimates of soil amino sugars (R2 = 0.74–0.21, RPDp = 1.99–1.12), except for the approximate quantitative estimation of muramic acid by models based on soil spectra at the western and the multisite scale (R2 = 0.82–0.80, RPDp = 2.33–2.21). We concluded that MIR and NIR models at regional and multisite scales can be used as a tool to monitor HWDC but that additional research is required for estimating soil amino sugars.

Micrometeorological Measurements Reveal Large Nitrous Oxide Losses during Spring Thaw in Alberta

Agricultural soils in Canada have been observed to emit a large pulse of nitrous oxide (N2O) gas during the spring thaw, representing a large percentage of the annual emissions. We report on three years of spring thaw N2O flux measurements taken at three Alberta agricultural sites: a crop production site (Crop), cattle winter-feeding site (WF), and a cattle winter-grazing site (WG). Soil fluxes were calculated with a micrometeorological technique based on the vertical gradient in N2O concentration above each site measured with an open-path (line-averaging) FTIR gas detector. The Crop and WG sites showed a clear N2O emission pulse lasting 10 to 25 days after thawing began. During this pulse there was a strong diurnal cycle in emissions that paralleled the cycle in near-surface soil temperature. The emission pulse was less pronounced at the WF site. The average spring thaw losses (over 25 to 31 days) were 5.3 (Crop), 7.0 (WF), and 8.0 (WG) kg N2O-N ha−1, representing 1 to 3.5% of the annual nitrogen input to the sites. These large losses are higher than found in most previous western Canadian studies, and generally higher than the annual losses estimated from the Intergovernmental Panel on Climate Change and Canadian National Inventory Report calculations. The high N2O losses may be explained by high soil nitrate levels which promoted rapid denitrification during thawing. The application of a high resolution (temporal) micrometeorological technique was critical to revealing these losses.

Soil nitrous oxide emissions from agricultural soils in Canada: Exploring relationships with soil, crop and climatic variables

National scale emissions of nitrous oxide (N2O) from agricultural soils are often estimated using a unique fertilizer-induced emission factor (EF); thereby neglecting how factors other than nitrogen input could impact emissions. In the present study, we compiled soil N2O flux data collected since 1990 on agricultural soils in Canada, to identify key soil and climate factors, and management practices that explain variations in N2O emissions and in EF. Stepwise regression analysis showed that the growing season precipitation was the most important factor impacting N2O emissions, and that cumulative N2O fluxes and EFs could be predicted using equations (R2 from 0.68 to 0.85) including two to five of the following variables: growing season precipitation, ratio of growing season precipitation to potential evapotranspiration, mean annual air temperature, crop type (annual or perennial), soil pH, texture and organic carbon content. We conclude that N2O EFs could be effectively stratified based on growing season precipitation, soil texture (coarse, medium and fine), type of N (synthetic and organic), and crop type (perennial and annual). We propose EFs that account for the dominant factors that modulate the nitrogen fertilizer-induced emissions and should improve regional and national estimates in Canada. They may also provide useful information for guiding the development of soil N2O emission quantification in other countries.

Modelling carbon dioxide emissions from agricultural soils in Canada

Agricultural soils are a leading source of atmospheric greenhouse gas (GHG) emissions and are major contributors to global climate change. Carbon dioxide (CO2) makes up 20% of the total GHG emitted from agricultural soil. Therefore, an evaluation of CO2 emissions from agricultural soil is necessary in order to make mitigation strategies for environmental efficiency and economic planning possible. However, quantification of CO2 emissions through experimental methods is constrained due to the large time and labour requirements for analysis. Therefore, a modelling approach is needed to achieve this objective. In this paper, the DeNitrification-DeComposition (DNDC), a process-based model, was modified to predict CO2 emissions for Canada from regional conditions. The modified DNDC model was applied at three experimental sites in the province of Saskatchewan. The results indicate that the simulations of the modified DNDC model are in good agreement with observations. The agricultural management of fertilization and irrigation were evaluated using scenario analysis. The simulated total annual CO2 flux changed on average by ±13% and ±1% following a ±50% variance of the total amount of N applied by fertilising and the total amount of water through irrigation applications, respectively. Therefore, careful management of irrigation and applications of fertiliser can help to reduce CO2 emissions from the agricultural sector.

Flexing the PECs: Predicting environmental concentrations of veterinary drugs in Canadian agricultural soils.

Veterinary drugs administered to food animals primarily enter ecosystems through the application of livestock waste to agricultural land. Although veterinary drugs are essential for protecting animal health, their entry into the environment may pose a risk for nontarget organisms. A means to predict environmental concentrations of new veterinary drug ingredients in soil is required to assess their environmental fate, distribution, and potential effects. The Canadian predicted environmental concentrations in soil (PECsoil) for new veterinary drug ingredients for use in intensively reared animals is based on the approach currently used by the European Medicines Agency for VICH Phase I environmental assessments. The calculation for the European Medicines Agency PECsoil can be adapted to account for regional animal husbandry and land use practices. Canadian agricultural practices for intensively reared cattle, pigs, and poultry differ substantially from those in the European Union. The development of PECsoil default values and livestock categories representative of typical Canadian animal production methods and nutrient management practices culminates several years of research and an extensive survey and analysis of the scientific literature, Canadian agricultural statistics, national and provincial management recommendations, veterinary product databases, and producers. A PECsoil can be used to rapidly identify new veterinary drugs intended for intensive livestock production that should undergo targeted ecotoxicity and fate testing. The Canadian PECsoil model is readily available, transparent, and requires minimal inputs to generate a screening level environmental assessment for veterinary drugs that can be refined if additional data are available. PECsoil values for a hypothetical veterinary drug dosage regimen are presented and discussed in an international context. Integr Environ Assess Manag 2017;13:331-341. © 2016 Her Majesty the Queen in Right of Canada. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of SETAC. Reproduced with the permission of the Minister of Health.

Scenario analysis of fertilizer management practices for N2O mitigation from corn systems in Canada

Effective management of nitrogen (N) fertilizer application by farmers provides great potential for reducing emissions of the potent greenhouse gas nitrous oxide (N2O). However, such potential is rarely achieved because our understanding of what practices (or combination of practices) lead to N2O reductions without compromising crop yields remains far from complete. Using scenario analysis with the process-based model DNDC, this study explored the effects of nine fertilizer practices on N2O emissions and crop yields from two corn production systems in Canada. The scenarios differed in: timing of fertilizer application, fertilizer rate, number of applications, fertilizer type, method of application and use of nitrification/urease inhibitors. Statistical analysis showed that during the initial calibration and validation stages the simulated results had no significant total error or bias compared to measured values, yet grain yield estimations warrant further model improvement. Sidedress fertilizer applications reduced yield-scaled N2O emissions by c. 60% compared to fall fertilization. Nitrification inhibitors further reduced yield-scaled N2O emissions by c. 10%; urease inhibitors had no effect on either N2O emissions or crop productivity. The combined adoption of split fertilizer application with inhibitors at a rate 10% lower than the conventional application rate (i.e. 150kgNha−1) was successful, but the benefits were lower than those achieved with single fertilization at sidedress. Our study provides a comprehensive assessment of fertilizer management practices that enables policy development regarding N2O mitigation from agricultural soils in Canada.

Sensitivity analysis for nitrogen inputs, nitrogen outputs, and changes in biofuel crop acreages for predicting residual soil nitrogen and nitrate leaching in Canadian agricultural soils

Substantial improvements have been made to the Canadian Agricultural Nitrogen Budget model (CANB) for estimating residual soil nitrogen (RSN) and the indicator of the risk of water contamination by nitrogen (IROWC-N). These included new algorithms for manure, fertilizer and biological fixation inputs and losses as well as the incorporation of a versatile soil moisture model. The new semi-dynamic model (CANB v 3.0) was compared to the static model (CANB 2.0) for estimating both RSN and IROWC-N. Sensitivity analysis of the RSN component using 2006 land use practices was also conducted and crop yield and N uptake were found to be the most sensitive parameters, followed by biological N2 fixation and the addition of fertilizer N and manure N. Land use scenarios were evaluated to examine if increasing the proportion of biofuel crops grown in Canada would change RSN and IROWC-N appreciably. The analyses demonstrated that the area of canola and maize crops could be increased in Canada by up to 40% to meet biofuel production demands without significantly changing RSN and IROWC-N.

Development of a method for estimating the likelihood of crack flow in Canadian agricultural soils at the landscape scale

Indicators of risk of water contamination by agricultural pollutants are developed in Canada to assess sustainability of agriculture. Crack flow (CF), a key pathway for sub-surface contaminant transport, is part of the transport-hydrology algorithm used in two of these risk indicators. The objective was to develop a methodology for predicting the likelihood of CF in Canadian agricultural soils at the landscape scale. The algorithm considers soil clay content, crack development followed by a runoff event based on water budget, tile drainage, and crops. More than 40% of Canadian farmlands had moderate to very high likelihood of CF, mainly in Manitoba, Ontario and Quebec, due to frequent runoffs on cracked clay soils potentially contributing to groundwater contamination. In Ontario and Quebec, farmlands with high CF likelihood correspond to regions under intensive tile drainage, which increases the risk of lateral translocation of contaminants to surface water bodies. Besides being a component of risk indicators of water contamination by phosphorus and coliforms, the CF algorithm and maps can be used to identify areas at risk of subsurface water contamination. Best management practices, adapted to reduce CF can then be targeted to these areas.Key words: Agrichemicals, contaminant transport, macropore flow, preferential flow, risk assessment, risk indicators

Application of food industry waste to agricultural soils mitigates green house gas emissions

Application of organic waste materials such as food processing and serving industry cooking oil waste (OFW) can recycle soil nitrate nitrogen (NO 3–N), which is otherwise prone to leaching after the harvest of crop. Nitrogen (N) recycling will not only reduce the amount of N fertilizer application for corn crop production but is also expected to mitigate green house gas (GHG) emissions by saving energy to be used for the production of the same amount of industrial fertilizer N required for the growth of corn crop. Application of OFW at 10 Mg solid ha −1 y −1 conserved 68 kg N ha −1 y −1 which ultimately saved 134 L diesel ha −1 y −1, which would otherwise be used for the production of fertilizer N as urea. Average fossil energy substitution value (FESV) of N conserved/recycled was calculated to be 93 US$ ha −1 y −1, which is about 13 million US$y −1. Potential amount of GHG mitigation through the application of OFW to agricultural soils in Canada is estimated to be 57 Gg CO 2Eq y −1.