Canadian Agroecosystems Research Articles

Trap cropping for insect pests in the Canadian Prairies: a review and a case study

AbstractThe Canadian Prairies are one of the major agricultural regions of the world in terms of cereal, oilseed and pulse crop production. With few exceptions, major insect pests like grasshoppers, flea beetles, Lygus bugs, wireworms and pea leaf weevils are controlled with insecticides. Wheat stem sawfly is managed through host plant resistance and endemic natural enemies, whereas cereal leaf beetle is managed through classical biological control. Large farms and short growing seasons in the region present logistical challenges to adopt time intensive pest management systems such as trap crops. Therefore, there is no adoption of trap crops even though some research has demonstrated their potential. In this article we present a brief overview of the pest status and management, and we summarize research on trap crops in the Prairies Ecozone and adjacent ecoregions. We conclude the review with some innovative research ideas to make trap cropping a more appealing pest management system in our quest to reduce dependency on chemical insecticides and increase the environmental resilience of Canadian agroecosystems.

Palmer amaranth (Amaranthus palmeri S. Wats.) and waterhemp (Amaranthus tuberculatus (Moq.) J.D. Sauer) biovigilance in Canadian Agro-ecosystems

The evolution and spread of herbicide-resistant weeds threatens long-term sustainability of Canadian agro-ecosystems. Herbicide-resistant weeds increase management inputs and costs, increase off-target and environmental exposure to pesticides, reduce yield quality and quantity, and impede harvest efficiency. Amaranthus species including Palmer amaranth ( Amaranthus palmeri S. Wats.) and waterhemp ( Amaranthus tuberculatus (Moq.) J.D. Sauer) are particularly concerning due to both their propensity towards herbicide resistance evolution, their history of invasion, and their spread in agro-ecosystems. A biovigilance approach is taken to build awareness of these pigweeds' initial invasion and spread in the USA. Characteristics of their identification, potential hybridization, and known herbicide resistance evolution are reviewed. Fourteen species of Amaranthus are found in Canada, nine of which (including waterhemp) possess herbicide-resistant biotypes. A total of 45 hybrids between various Canadian Amaranthus species with each other or Palmer amaranth have been noted. Hybrids have been experimentally produced or observed from herbarium specimens, with three cases of herbicide resistance transfer notably with Palmer amaranth or waterhemp. Mitigation strategies will depend on successful species identification and herbicide resistance status determination. Common pathways for Palmer amaranth introductions in the northern USA include both animal feed systems with grain screenings and crop production systems including seed and equipment contamination. Regional awareness campaigns will be critical to support Canadian farmers in identifying and quickly mitigating invasions of Palmer amaranth and waterhemp to prevent establishment and spread of infestations into new areas.

The story of long-term research sites and soil health in Canadian agriculture

Canada's interest in agricultural lands has changed with time from a desire of crop yields at Confederation through to discussions in the Senate on adaptation and resilience in 2018. Long-term research experiments (LTRs) have been present and utilized by federal and university researchers to provide answers throughout. Here we highlight the importance of LTRs by identifying the historical context of LTRs and soil health research in Canada. We then briefly describe the history and key results from select LTRs and illustrate the wealth of information collected from the North American Project to Evaluate Soil Health Measurements cross-country point-in-time soil sampling from these LTRs. We discuss the LTRs, and the knowledge gained from them, with the hope that by showing the distinctive narratives associated with each of these study sites, researchers will be inspired to use them to address their research questions and make sound predictions to facilitate the adaptation of Canadian agroecosystems to climate challenges. Through identifying the value generated by these unique LTRs, we hope that the importance of these sites will inspire not only their continued maintenance but also the next generation of LTRs.

Summer habitat use and movements of invasive wild pigs (Sus scrofa) in Canadian agro-ecosystems

Resource selection informs understanding of a species’ ecology and is especially pertinent for invasive species. Since introduced to Canada, wild pigs ( Sus scrofa Linnaeus, 1978) remain understudied despite recognized negative impacts on native and agricultural systems globally. Elsewhere in North America, pigs typically use forests and forage in agricultural crops. We hypothesized Canadian wild pigs would behave similarly, and using GPS locations from 15 individuals, we examined diel and seasonal resource selection and movement in the Canadian prairie region. Forests were predominately selected during the day, while corn ( Zea mays L.), oilseeds, and wheat ( Triticum aestivum L.) were predominately selected at night. Forests and corn were consistently selected throughout the growing season. Wetlands and forests showed greater use rates than other habitats, with evident trade-offs as crop use increased with the timing of maturation. Activity was consistent with foraging in growing crops. Results indicate diel patterns were likely a function of short-term needs to avoid daytime anthropogenic risk, while seasonal patterns demonstrate how habitats that fill multiple functional roles — food, cover, and thermoregulation — can be optimized. Understanding selection by invasive species is an important step in understanding their potential environmental impacts in novel environments and informs their management.

An updated nitrogen budget for Canadian agroecosystems

Nitrogen (N) is an essential ingredient for the production of food in agricultural systems. As the use of industrial fertilizers has risen over time, so too have concerns relating to N losses from these systems and the contamination of air and water, climate change impacts and biodiversity losses these cause. In order to balance continuing and improving agricultural productivity with the potential for N losses, improved estimates of N additions, N use efficiency (NUE, the ratio between N inputs and N exported in products) and N losses to the environment are crucial.We estimated the N balance for Canadian agroecosystems based on 2016 data and used similar but updated assumptions and coefficients to recalculate estimates from a previous study based on 1996 data. This approach calculated the overall recovery of N in Canadian agriculture by imposing a system boundary around all farmlands, and then estimating the N balance within that area. In 2016, a total of 3.80 Tg of N were input to the agroecosystems from biological (0.94 Tg), industrial (2.54 Tg) and atmospheric (0.32 Tg) fixation, compared with 2.42 Tg in 1996 (a 57 % increase). Between 1996 and 2016, crop NUE increased from 46.7 to 50.8 %, livestock NUE from 21.2 to 22.8 %, and agroecosystem NUE from 58.3 to 59.5 %. Due to higher total N inputs and a decrease in the area of agricultural land, the total mass of N added to the system and not exported in crop and livestock products rose by over 50 % (from 1.01 to 1.54 Tg). This indicates that although N use efficiencies improved over the 20-year period, the total mass of N potentially lost to the environment increased significantly. To improve N use efficiencies and reduce N losses, management strategies must be tailored to different conditions across Canada’s agricultural landscape, adopted at all stages of agricultural production and consider the multiple flows and feedbacks of N within the agroecosystem. Future research should aim not just at improving N use efficiency, but also at tracing more precisely the fate of N unaccounted for, so that losses can at least be steered away from more pernicious routes.

Enhancing the Social and Natural Capital of Canadian Agro-Ecosystems through Incentive-Based “Alternative Land Use Services” (ALUS) Programs: Recurring Themes and Emerging Lessons

Alternative Land Use Services (ALUS) is an incentive-based program established in Canada to pay farmers for their voluntary delivery of ecosystem services (ES). All seven ALUS programs across the country were examined using a standardized case-study approach based on site visits, reading internal documents, attending program meetings, and engaging in semi-structured interviews with program administrators, participating farmers, and advisory board members. Direct content analysis was used to highlight recurrent themes and emerging lessons in relation to the salient particulars of program physical location, administration framework, delivery of ES, and development and receipt by communities. Our three major findings are: 1) Overall, ALUS has been judged by participants to be a very successful program, whose strength is that it is completely voluntary, non-permanent, and readily adaptable to each location’s environmental conditions, economic funding base, and cultural milieu. 2) One serious shortcoming of all ALUS programs is a general lack of quantifiable data on their ability to increase ES. Instead, environmental benefits are either assumed or based on the idea that the areal extent of enrolled land is the sole measure of its environmental worth. 3) It may be that the social impact of ALUS is its greatest success. In this regard, for farmers, it is the process of engaging in land-use decision making and the recognition of their role as environmental stewards that is a bigger motivation for participating in an ALUS program than the modest financial incentives which they receive.

Energy in a woodland-livestock agroecosystem: Prince Edward Island, Canada, 1870–2010

This article presents historic energy profiles in order to understand the changing roles of three critical energy flows in eastern Canadian agroecosystems. The first flow is the societally useful energy that farms produced in crops, animal products, and forest resources. This flow stabilized after colonization and then intensified with the introduction of fossil fuel inputs. The second flow consists of these external inputs, including human labor and the energy embodied in machinery, fuel, and fertilizers. The final flow is the biomass from within the agroecosystem itself. Farmers removed this biomass from their final produce and recycled it as feed for animals, seed for crops, and fencing for livestock management. This article presents evidence on these energy flows from a set of case studies in Northeastern North America. Prince Edward Island (PEI) offers a study of energy transitions in a frontier agroecosystem at the farm, township, county, and the bounded provincial scales. This study uses time points from the 1881, 1931, 1951, and 1996 censuses, as well other statistics. The energy in land produce remained stable during the socio-ecological transition because of the importance of forest products. Results at the sub-county scale demonstrate complementary components within the larger provincial system, and the example of one farm (1877–1892) illustrates specialized energy strategies within the advanced organic regime. After the socio-ecological transition, external inputs remained lower than expected, but together with the steady growth of livestock, they ensured that biomass energy inputs were more productive in the mineral regime than they had been in the organic period.

Optimizing Seeding Dates and Rates for Canola Production in the Humid Eastern Canadian Agroecosystems

Optimum seeding date (OSD) and seeding rate is an important management practice to improve the performance of canola (Brassica napus L.) production. A field study was conducted to investigate the influence of seeding date and rate on plant stand count, yield components, yield, and seed oil and protein concentrations, and to develop a location‐sensitive model for estimating OSD for maximizing canola yield. The factorial experiment of three seeding dates (early, intermediate, and late) and three seeding rates (2.5, 5.0, and 7.5 kg ha−1) was performed in 2011 and 2012 at seven locations across eastern Canada. An independent dataset from an additional 2‐yr field experiment at the Ottawa site was used for model verification. Our data showed that seed yield, seed oil, and pod number per plant were significantly affected by seeding date and seeding rate. The greatest yield and seed oil concentration were obtained with the early seeding in most site‐years. The OSD was a quadratic function of the long‐term (30 yr) average daily minimum air temperature (Tmin) in April and May with R2 = 0.98, P < 0.01 and SE = 2.6 d. Increasing seeding rate from 2.5 to 5.0 kg ha−1 increased seed yield for early‐seeded canola in most site‐years but the yield did not increase with further increases in seeding rate. Early seeding at 5.0 kg ha−1 is therefore recommended as the optimum seeding rate across eastern Canada. Quantitative relationship between optimum seeding date and mean minimum temperature in April and May. A regression model to predict optimum seeding date for spring canola. A suitable seeding rate for canola production in eastern Canada. The impact of seeding date on canola seed oil and protein concentration. Canola yield and yield components as affected by seeding date and rate.

Manipulating lignin deposition

Schuetz, M., Douglas, C., Samuels, L. and Ellis, B. 2014. Manipulating lignin deposition. Can. J. Plant Sci. 94: 1043–1049. Since lignin represents one of most durable forms of fixed carbon in plant biomass, we hypothesized that increasing root lignin content for crops whose root systems remained in the soil after harvest would elevate the total amount of carbon retained in the soil in Canadian agroecosystems. The immediate goal of this Greencrop project was, therefore, to gain a better understanding of the molecular mechanisms that control deposition of the lignin polymer in plant cell walls, with a view to eventually manipulating the quantity and location of lignin in crop plant root systems. To this end, we examined two classes of Arabidopsis thaliana proteins – transcription factors, which are believed to play crucial roles in regulating lignin biosynthesis, and ATP binding cassette transporters, which are putative lignin precursor transporters. These studies revealed that a complex network of interacting transcriptional regulators is involved in activating and suppressing the expression of key genes required for secondary cell wall deposition and lignification.

Manipulating lignin deposition

Schuetz, M., Douglas, C., Samuels, L. and Ellis, B. 2014. Manipulating lignin deposition. Can. J. Plant Sci. 94: 1043-1049. Since lignin represents one of most durable forms of fixed carbon in plant biomass, we hypothesized that increasing root lignin content for crops whose root systems remained in the soil after harvest would elevate the total amount of carbon retained in the soil in Canadian agroecosystems. The immediate goal of this Greencrop project was, therefore, to gain a better understanding of the molecular mechanisms that control deposition of the lignin polymer in plant cell walls, with a view to eventually manipulating the quantity and location of lignin in crop plant root systems. To this end, we examined two classes of Arabidopsis thaliana proteins - transcription factors, which are believed to play crucial roles in regulating lignin biosynthesis, and ATP binding cassette transporters, which are putative lignin precursor transporters. These studies revealed that a complex network of interac...

First Report of the Root-Lesion Nematode, Pratylenchus alleni Associated with Damage on Soybean in Quebec, Canada.

In eastern Canada, soybean, Glycine max (L.) Merr., is the most important cultivated legume species. In 2011, the provinces of Ontario and Quebec had 987,400 and 300,000 ha of soybean production, respectively. Root-lesion nematodes, Pratylenchus spp., are the most prevalent plant-parasitic nematodes in Canadian agroecosystems and can affect many crops (3). In 2011, irregular patches of stunted soybean plants were observed for the first time in a 10-ha soybean field grown on a light texture soil in St. Anicet, Quebec (45°4'50.51″N, 74°21'18.56″W). Yield reduction in damaged plots ranged from 38 to 54% when compared with asymptomatic adjacent plots. The field was sown with soybean cv. PRO 2715R (PRO Seeds of Canada, Woodstock, ON), a Roundup Ready cultivar of 2,750 CHU, at 100 kg/ha. Soil analysis revealed a uniform pH of 6.0 ± 0.2 on a gravelly sandy soil (81% sand, 10% loam, 9% clay, and 4% organic matter). On 7 October 2011, root samples were collected from 10 randomly selected damaged patches, washed under running water, and deposited in a mist chamber for a 14-day extraction period. Specimens were stored in tap water at 4°C before identification. Based on morphological characteristics, 26 individual specimens were examined (14 females, 11 males, one juvenile) and were all identified as Pratylenchus alleni Ferris, 1961 (2). Genomic DNA was extracted from individual larvae and the internal transcribed spacers (ITS) region was amplified. RFLP analysis with five restriction enzymes (CfoI, DdeI, HindIII, HpaII, and PstI) showed that the banding pattern for this species was different from those of 18 other major Pratylenchus species (4). Sequence of ITS regions of this population (GenBank Accession No. JX081545) confirmed genus identification but showed only limited homology (<85%) with the 20 Pratylenchus species available in the database at this time. Based on the morphological identification and the ITS sequence divergence with other important species, the sequence was deposited as the first P. alleni accession in GenBank. In the United States, the pathogenicity of P. alleni to soybean is well established (1). To our knowledge, this is the first report of P. alleni occurrence and damage to soybean in Canada. The outbreak of this root-lesion nematode will pose a new challenge for crop management since no registered compounds are currently available against this pest in soybean in Canada.

Integration of Greenhouse Gas Emissions and Removals from Canadian Agroecosystems: Preface

Integration of Greenhouse Gas Emissions and Removals from Canadian Agroecosystems: Preface

Estimates of direct nitrous oxide emissions from Canadian agroecosystems and their uncertainties

Using a revised Intergovernmental Panel on Climate Change (IPCC) methodology and the process-based model DeNitrification and DeComposition (DNDC), we estimated N2O emissions from agroecosystems in Canada for each census year from 1981 to 2001. Based on the IPCC methodology, direct emissions of N2O ranged from 12.9 to 17.3 with an average of 15.1 Tg CO2 equivalents, while the DNDC model predicted values from 16.0 to 24.3 with an average of 20.8 Tg CO2 equivalents over the same period, and showed a large interannual variation reflecting weather variability. On a provincial basis, emissions estimated by IPCC and DNDC methods were highest in Alberta, Saskatchewan and Ontario, intermediate for Manitoba and Quebec and lowest in British Columbia and the Atlantic provinces. The greatest source of emissions estimated by the IPCC method was from N fertilizer (avg. 6.32 Tg CO2 equiv. in Canada), followed by crop residues (4.24), pasture range and paddocks (PRP) (2.77), and manure (1.65). All sources of emissions, but especially those from fertilizers, increased moderately over time. Monte Carlo Simulation was used to determine the uncertainty associated with the 2001 emission estimates for both IPCC and DNDC methodologies. The simulation generated most likely values of 19.2 and 16.0 Tg CO2 equivalents for IPCC and DNDC, respectively, with uncertainties of 37 and 41%, respectively. Values for the IPCC estimates varied between 28% for PRP and manure and 50% for N fertilizer and crop residues. At the provincial level, uncertainty ranged between 15 and 47% with higher values on the prairies. Sensitivity analyses for IPCC estimates showed crop residues as the most important source of uncertainty followed by synthetic N-fertilizers. Our analysis demonstrated that N2O emissions can be effectively estimated by both the DNDC and IPCC methods and that their uncertainties can be effectively estimated by Monte Carlo Simulation. Key words: Nitrous oxide, IPCC, DNDC model, Uncertainty analysis, Monte Carlo Simulation

An approach for estimating net primary productivity and annual carbon inputs to soil for common agricultural crops in Canada

The current interest in characterizing, predicting and managing soil C dynamics has focused attention on making estimates of C inputs to soil more accurate and precise. Net primary productivity (NPP) provides the inputs of carbon (C) in ecosystems and determines the amount of photosynthetically fixed C that can potentially be sequestered in soil organic matter . We present a method for estimating NPP and annual C inputs to soil for some common Canadian agroecosystems , using a series of plant C allocation coefficients for each crop type across the country. The root-derived C in these coefficients was estimated by reviewing studies reporting information on plant shoot-to-root (S:R) ratios ( n = 168). Mean S:R ratios for annual crops were highest for small-grain cereals (7.4), followed by corn (5.6) and soybeans (5.2), and lowest for forages (1.6). The review also showed considerable uncertainty (coefficient of variation for S:R ratios of ∼50% for annual crops and ∼75% for perennial forages) in estimating below-ground NPP (BNPP) in agroecosystems; uncertainty was similar to that for Canadian boreal forests . The BNPP (including extra-root C) was lower for annual crops (∼20% of NPP) than for perennial forages (∼50%). The latter was similar to estimates for relative below-ground C allocation in other Canadian natural ecosystems such as mixed grasslands and forests. The proposed method is easy to use, specific for particular crops, management practices, and driven by agronomic yields. It can be readily up-dated with new experimental results and measurements of parameters used to quantify the accumulation and distribution of photosynthetically fixed C in different types of crops.

Towards optimum sampling for regional-scale N2O emission monitoring in Canada

There is an increasing need for field monitoring studies of N2O emissions to assess the reliability of process models. Our goal is to review the issues surrounding the design of monitoring and regional upscaling of fieldmeasured N2O emissions for Canadian conditions. Management history creates a range of controlling conditions and emission responses for each land use present in the study region and multiple fields should be sampled within each land use class. The requirement for multiple sample fields necessitates chamber-based sampling designs (ideally in conjunction with site-specific micrometeorological measurements). Uniformly minimum variance unbiased (UMVU) estimators have been recommended for estimation of the mean and variance of the sample distributions, but use of these estimators is limited where zero or negative values occur. Three basic annual emission patterns are observed across a range of N2O studies: background, seasonal, and event + seasonal. The event + seasonal pattern (where short duration, high emission events are superimposed on an underlying seasonal pattern) is common in Canadian agroecosystems. Background and seasonal annual patterns can be effectively captured with biweekly or even triweekly samplings. For the event + seasonal patterns more frequent samplings at periods when emission are believed to be higher (e.g., snow melt or post-fertilization events) are required. Linear interpolation of emissions between the sporadic measurements is the simplest and most reproducible method of temporal interpolation. Spatial extrapolation of the measured emissions is typically done by a measure and multiply approach, where the measured emissions for a given class are multiplied by the area of the class. The methods used to define the soil wetness, land use, and management classes should be clearly defined and consistently applied. The lack of information on the duration and magnitude of event-based emissions and the diurnal pattern of emissions is a major limitation to temporal interpolation. Key words: Greenhouse gas, upscaling, geographical information systems, landscape

Toward Improved Coefficients for Predicting Direct N2O Emissions from Soil in Canadian Agroecosystems

Agricultural soils emit nitrous oxide (N2O), a potent greenhouse gas. Predicting and mitigating N2O emissions is not easy. To derive national coefficients for N2O emissions from soil, we collated over 400 treatment evaluations (measurements) of N2O fluxes from farming systems in various ecoregions across Canada. A simple linear coefficient for fertilizer-induced emission of N2O in non-manured soils (1.18% of N applied) was comparable to that used by the Intergovernmental Panel on Climate Change (IPCC) (1.25% of N applied). Emissions were correlated to soil and crop management practices (manure addition, N fertilizer addition and inclusion of legumes in the rotation) as well as to annual precipitation. The effect of tillage on emissions was inconsistent, varying among experiments and even within experiments from year to year. In humid regions (e.g., Eastern Canada) no-tillage tended to enhance N2O emissions; in arid regions (e.g., Western Prairies) no-tillage sometimes reduced emissions. The variability of N2O fluxes shows that we cannot yet always distinguish between potential mitigation practices with small (e.g., <10%) differences in emission. Our analysis also emphasizes the need for developing consistent experimental approaches (e.g., ‘control’ treatments) and methodologies (i.e. measurement period lengths) for estimating N2O emissions.

Characterizing soil biota in Canadian agroecosystems: State of knowledge in relation to soil organic matter

Organic residues resulting from crop and animal production either become incorporated in the soil or remain on the surface and, thus, provide much of the nutrient and energy sources for many soil organisms. Characterizing the response of soil biota to these organic materials is a challenging undertaking due to the complexity of the soil ecosystem with respect to the magnitude of biodiversity involved, the possibilities for interrelationships with biochemical and biophysical processes, and the immense range of scale of observation from particle, through to aggregate, field, landscape and regional levels. The objectives of this paper were to review the available research pertaining to Canadian agroecosystems, which characterize the response of soil biota to soil organic matter dynamics, and to identify the issues, challenges and knowledge gaps. The response by soil organisms is discussed from two approaches: (1) their state of occurrence in terms of population response to soil organic matter as a nutrient and carbon/energy source, and (2) the extent of their influence in contributing to organic matter dynamics, that is, assessing their functional role. For the most part, Canadian research has emphasized comparative studies based on population responses by broad soil biota groups to soil organic matter additions or losses as an outcome of undertaking various agronomic practices. Studies that evaluate the extent of contributions by soil biota to soil organic matter dynamics are few, and rare at the species level. For Canadian agroecosystems, there is currently a great need for research initiatives that address the immense knowledge gaps that exist in relation to (a) identifying the specific contributions to soil organic matter processes and interactions of soil biota both at species and community level, (b) predicting outcomes of the contributions of soil biota groups in regulating or controlling soil organic matter processes both spatially and temporally across landscapes, and (c) assessing the risk to soil biodiversity in various agroecosystems in being able to sustain these functional roles. Key words: Soil biota, functional role, soil organic matter, agroecosystems, ecosystem services

Acari and Collembola biodiversity in Canadian agricultural soils

In Canadian agricultural soils, mites (Acari) are the most diverse and abundant arthropods. In comparison with other arachnids, mites are notable for their small size, diverse feeding habits, often complex life histories, and the range of habitats in which they live. Collembola are also abundant and diverse in soil and litter, they are in the same size range as the Acari, and for that reason the two groups are often combined in soil ecological studies as “microarthropods ”. This paper provides a descriptive overview of the state of our knowledge on the taxonomy of these arthropods. It reviews the literature on biology and ecology of microarthropods in Canadian agroecosystems, especially on implications of various agricultural practices for their diversity and population structure. It discusses the research challenges in taxonomy and ecology to address effective use of this biodiversity in Canadian agroecosystems. Key words: Acari, Collembola, microarthropods, taxonomy, ecology

The fate of nitrogen in agroecosystems: An illustration using Canadian estimates

Agroecosystems rely on inputs of nitrogen (N) to sustain productivity. But added N can leak into adjacent environments, affecting the health of other ecosystems and their inhabitants. Worries about global warming have cast further attention on the N cycle in farmlands because farms are a main source of N2O, and because carbon sequestration, proposed to help reduce CO2 loads, requires a build-up of N. Our objective was to estimate, as an illustrative example, the net N balance of Canadian agroecosystems in 1996 and then infer some hypotheses about the routes of N loss, their magnitude, and ways of reducing them. We defined agroecosystems as all agricultural lands in Canada including soil to 1 m depth and all biota, except humans. Only net flows of N across those boundaries were counted in our balance – all others represent internal cycling. Based on our estimates, about 2.35 Tg N entered Canadian agroecosystems from biological fixation, fertilizers, and atmospheric deposition (excluding re-deposited NH3). In the same year, about 1.03 Tg N were exported in crop products and 0.19 Tg were exported in animals and animal products. Consequently, N inputs exceed exports in products by about 1.13 Tg, a surplus that is either accumulating in agroecosystems or lost to the environment. Because potential soil organic matter gains can account for only a small part of the surplus N, most is probably lost to air or groundwater. Our finding, that N losses amount to almost half of N added, concurs with field experiments that show crop recovery of added N in a given year is often not more than 60%. Better management may reduce the fraction lost somewhat but, because N in ecosystems eventually cycles back to N2, substantive gains in efficiency may not come easily. As well as trying to reduce losses, research might also focus on steering losses directly to N2, away from more harmful intermediates. If some of the `missing N' can be assimilated into organic matter, agricultural soils in Canada may need little added N to achieve C sequestration targets.

The response of soil quality indicators to conservation management

The response of soil quality attributes to management practices across a diverse range of farming systems is key to identifying a robust minimum data set (MDS). The objectives of this study were to compare the response and consistency of different soil organic matter (SOM) attributes to changes in soil management practices in eastern Canadian agroecosystems. Soil samples (0–10 cm) were obtained at sites of several replicated experiments throughout eastern Canada, and 16 paired comparisons were selected to determine the effect of conservation (no-tillage, rotations, organic amendments) versus conventional (fall moldboard plowing, continuous cropping, no organic amendments) management practices. A sensitivity index was calculated for each of the attributes by dividing the values for conservation treatments with their conventionally managed counterparts (i.e., Conservation/Conventional). The index showed that light fraction (LF) N (1.58) and macro-organic matter-N (MOM-N) (1.54) were the most sensitive SOM attributes to conservation management practices. Light fraction-C (LF-C), macro-organic matter-C (MOM-C) and microbial biomass-C (MB-C) also showed high sensitivity to conservation management (1.48, 1.34 and 1.44, respectively). The sensitivity index for carbohydrates, whole soil C and total N were 1.23, 1.16 and 1.17, respectively. However, the Friedman two-way analysis of variance test indicated that the sensitivity of the different attributes to conservation management was site specific. For example, although LF-N was highly ranked, it did not respond as frequently as most of the other attributes. A non-parametric sign test showed that whole soil C and N provided the most consistent response to conservation management. The average sensitivity index was highest for the amendment (1.82) followed by the tillage (1.26) and rotational (1.14) conservation management practices, suggesting that organic amendments had the greatest impact on most of the attributes. These results suggest that for eastern Canadian soils, use of MOM-C and MOM-N, MB-C and whole soil C would provide a useful, easy to measure and robust MDS. Key words: Soil quality indicators, response, conservation management