• Authors:
    • Lupwayi, N.
    • Haq, A.
    • Arshad, M.
    • Soon, Y.
  • Source: Soil & Tillage Research
  • Volume: 95
  • Issue: 1/2
  • Year: 2007
  • Summary: Information on which management practices can enhance soil organic matter (SOM) content and quality can be useful for developing sustainable crop production systems. We tested the influence of 12 years of no-till (NT) versus conventional tillage (CT), and four crop sequences on the organic C pools of a Grey Luvisolic sandy loam soil in northwestern Alberta, Canada. The crop sequences were: continuous wheat ( Triticum aestivum L.), field pea ( Pisum sativum L.)-wheat-canola ( Brassica rapa L.)-wheat, red clover ( Trifolium pratense L.) green manure-wheat-canola-wheat/red clover and fallow-wheat-canola-wheat. Soil samples from 1992, when the study was initiated, and 1996, 2000 and 2004 were analysed for total organic C (TOC), the light fraction (LF) and its C content, and water-soluble and mineralizable C. Total organic C in the top 15 cm of soil was higher in the red clover rotation than either the pea or fallow rotation by 1996. The tillage effect became significant only in 2004 with NT having a higher TOC than CT. The LF dry matter (DM) increased from 6.9 g kg -1 soil in 1992 to a range of 10-13 g kg -1 in 2000 and 2004. It was higher under NT than CT in 2 of 3 years and in the red clover rotation than the pea or fallow rotation in 1 of 3 years. The LF C content exhibited a similar trend as LF DM. The water-soluble and mineralizable C pools were not affected by tillage but decreased with time. Among crop rotations, the red clover rotation tended to result in higher levels of hot water-soluble and mineralizable C. It is concluded that tillage had a greater influence than crop rotation on the LF DM and LF C (as indicators of C storage), whereas the converse effect applied to mineralizable C and, to a lesser degree, hot water-soluble C (as indicators of SOM quality).
  • Authors:
    • Dosdall, L. M.
    • Moyer, J. R.
    • Clayton, G. W.
    • Harker, K. N.
    • Blackshaw, R. E.
    • O'Donovan, J. T.
    • Maurice, D. C.
    • Turkington, T. K.
  • Source: Crop Protection
  • Volume: 26
  • Issue: 3
  • Year: 2007
  • Summary: In western Canada, the move to integrated weed management (IWM) with reduced dependence on herbicides is being driven by low crop prices, weed resistance to herbicides, and environmental concerns. A rational step when implementing IWM is to determine if herbicide application is required in the first place. Crop yield loss models have been developed to assist with this decision. However, the weed economic threshold will be influenced considerably by management practices. Field studies showed that enhancing crop competitiveness through planting competitive varieties at relatively high seeding rates and through strategic fertilizer placement including sub-surface banded or point-injected nitrogen can reduce the impact of weeds on crop yield and the amount of weed seed entering the soil seed bank. Enhancing crop competitiveness also improved herbicide performance, especially when herbicides were applied at reduced doses. The inclusion of an early-cut silage crop in a rotation dramatically reduced wild oat ( Avena fatua L.) populations in barley ( Hordeum vulgare L.) while growing sweet clover ( Melilotus officinalis (L.) Lam) as a green manure in rotation with cereal and oilseed crops showed tremendous potential to suppress weeds. Other studies demonstrated that weed management should not be considered in isolation since it can influence the severity of alternative pests, for example, damage due to Delia spp. in canola ( Brassica napus L.). Further studies are required to examine the cumulative long-term effects of integrating the various weed management practices on all components of the crop ecosystem including weeds, diseases and insects.
  • Authors:
    • Holm, F. A.
    • Sapsford, K. L.
    • Cathcart, J.
    • Hall, L. M.
    • Clayton, G. W.
    • Harker, K. N.
    • O'Donovan, J. T.
    • Hacault, K.
  • Source: Weed Science
  • Volume: 55
  • Issue: 1
  • Year: 2007
  • Summary: There is no published information on the impact of volunteer barley on wheat yield loss or on the economics of controlling barley with a herbicide. With the registration of imazamox-resistant wheat, it is now possible to control volunteer barley in wheat. Thus, the likelihood of growing wheat in rotation with barley may increase. Field experiments were conducted in 2003 and 2004 at Beaverlodge, Lacombe, and Edmonton, AB, Canada, and Saskatoon, SK, Canada, to determine the impact of volunteer barley on yield of imazamox-resistant spring wheat seeded at relatively low (100 kg ha(-1)) and high (175 kg ha(-1)) rates. Barley was seeded at different densities to simulate volunteer barley infestations. Regression analysis indicated that wheat-plant density influenced the effects of volunteer barley interference on wheat yield loss, economic threshold values, and volunteer barley fecundity among locations and years. Econornic thresholds varied from as few volunteer barley plants as 3 m(-2) at Beaverlodge in 2003 and 2004 to 48 m(-2) at Lacombe in 2003. In most cases, wheat yield loss and volunteer barley fecundity were lower and economic thresholds were higher when wheat was seeded at the higher rate. For example, averaged over both years at Beaverlodge initial slope values (percentage of wheat yield loss at low barley density) were 4.5 and 1.7%, and economic threshold values of volunteer barley plants were 3 m(-2) and 8 m(-2) at low and high wheat seeding rates, respectively. Results indicate that volunteer barley can be highly competitive in wheat, but yield losses and wheat seed contamination due to volunteer barley can be alleviated by seeding wheat at a relatively high rate.
  • Authors:
    • Liebig, M. A.
    • Merrill, S. D.
    • Krupinsky, J. M.
    • Tanaka, D. L.
    • Hanson, J. D.
  • Source: Agronomy Journal
  • Volume: 99
  • Issue: 4
  • Year: 2007
  • Summary: Producers need to know how to sequence crops to develop sustainable dynamic cropping systems that take advantage of inherent internal resources, such as crop synergism, nutrient cycling, and soil water, and capitalize on external resources, such as weather, markets, and government programs. The objective of our research was to determine influences of previous crop and crop residues (crop sequence) on relative seed and residue yield and precipitation-use efficiency (PUE) for the no-till production of buckwheat ( Fagopyrum esculentum Moench), canola ( Brassica napus L.), chickpea ( Cicer arietinum L.), corn ( Zea mays L.), dry pea ( Pisum sativum L.), grain sorghum ( Sorghum bicolor L.), lentil ( Lens culinaris Medik.), proso millet ( Panicum miliaceum L.), sunflower ( Helianthus annus L.), and spring wheat ( Triticum aestivum L.) grown in the northern Great Plains. Relative seed yield in 2003 for eight of the 10 crops resulted in synergistic effects when the previous crop was dry pea or lentil, compared with each crop grown on its own residue. Buckwheat, corn, and sunflower residues were antagonistic to chickpea relative seed yield. In 2004, highest relative seed yield for eight of the 10 crops occurred when dry pea was the previous crop. Relative residue yield followed a pattern similar to relative seed yield. The PUE overall means fluctuated for seven of the 10 crops both years, but those of dry pea, sunflower, and spring wheat remained somewhat constant, suggesting these crops may have mechanisms for consistent PUE and were not as dependent on growing season precipitation distribution as the other seven crops. Sustainable cropping systems in the northern Great Plains will approach an optimal scheme of crop sequencing by taking advantage of synergisms and avoiding antagonisms that occur among crops and previous crop residues.
  • Authors:
    • VandenBygaart, A. J.
  • Source: Canadian Journal of Soil Science
  • Volume: 86
  • Issue: 3
  • Year: 2006
  • Summary: The distribution of soil organic carbon (SOC) in the landscape is governed by multiple factors and processes occurring at multiple scales. Thus, an understanding of landscape processes and pedology should aid in designing approaches to study SOC stock changes. Numerous factors affect distribution of SOC in the landscape at varying spatial and temporal scales. Each of these is summarized to set the stage for outlining a proposed approach to monitoring SOC in the agricultural landscape. Many tools are used to assess the variability of soil properties at varying spatial scales. Pedological knowledge and interpretation of landscape processes can be used to understand the spatial distribution of SOC in the landscape. I show that semi-variograms and the minimum detectable difference may be of limited value in deriving a universal approach to assess SOC change. Issues to be considered or resolved before initiating a monitoring system include depth of sampling and influence of management, compositing and sub-sampling, changes in bulk density, landscape effects and SOC dynamics. After considering these issues, I propose an approach to monitor SOC stock change in agroecosystems, acknowledging that any methodology likely cannot be strictly and universally applicable. The approach considers issues such as location, plot layout, and experimental and statistical design. Such an approach, derived from a landscape and pedology perspective, may make the measurement and verification of SOC at varying scales a less daunting task.
  • Authors:
    • Angers, D. A.
    • VandenBygaart, A. J.
  • Source: Canadian Journal of Soil Science
  • Volume: 86
  • Issue: 3
  • Year: 2006
  • Summary: In response to Kyoto Protocol commitments, countries can elect agricultural carbon sinks to offset emissions from other sectors, but they need to verify soil organic carbon (SOC) stock change. We summarize issues we see as barriers to obtaining accurate measures of SOC change, including: soil depth, bulk density and equivalent soil mass, representation of landscape components, experimental design, and the equilibrium status of the SOC. If the entire plow depth is not considered, rates of SOC storage under conservation compared with conventional tillage can be overstated. Bulk density must be measured to report SOC stock on an area basis. More critical still is the need to report SOC stock on an equivalent mass basis to normalize the effects of management on bulk deisity. Most experiments comparing SOC under differing management have been conducted in small, flat research plots. Although results obtained from these long-term experiments have been useful to develop and validate SOC prediction models, they do not adequately consider landscape effects. Traditional agronomic experimental designs can be inefficient for assessing small changes in SOC stock within large spatial variability. Sampling designs are suggested to improve statistical power and sensitivity in detecting changes in SOC stocks over short time periods.
  • Authors:
    • Jakas, M. C. Q.
    • Rosenberg, N. J.
    • McGill, W. B.
    • Williams, J. R.
    • Izaurralde, R. C.
  • Source: Ecological Modelling
  • Volume: 192
  • Issue: 3-4
  • Year: 2006
  • Summary: Soil carbon sequestration (SCS) has emerged as a technology with significant potential to help stabilize atmospheric CO2 concentrations and thus reduce the threat of global warming. Methods and models are needed to evaluate and recommend SCS practices based on their effects on carbon dynamics and environmental quality. Environment Policy Integrated Climate (EPIC) is a widely used and tested model for simulating many agroecosystem processes including plant growth, crop yield, tillage, wind and water erosion, runoff, soil density, and leaching. Here we describe new C and N modules developed in EPIC built on concepts from the Century model to connect the simulation of soil C dynamics to crop management, tillage methods, and erosion processes. The added C and N routines interact directly with soil moisture, temperature, erosion, tillage, soil density, leaching, and translocation functions in EPIC. Equations were also added to describe the effects of soil texture on soil C stabilization. Lignin concentration is modeled as a sigmoidal function of plant age. EPIC was tested against data from a conservation reserve program (CRP) 6-year experiment at five sites in three U.S. Great Plains states and a 61-year long-term agronomic experiment near Breton, Canada. Mean square deviations (MSD) calculated for CRP sites were less than 0.01 (kg C m(-2))(2), except for one site where it reached 0.025 (kg C m(-2))(2). MSD values in the 61-year experiment ranged between 0.047 and 0.077 (kg C m(-2))(2). The version of the EPIC model presented and tested here contains the necessary algorithms to simulate SCS and improve understanding of the interactions among soil erosion, C dynamics, and tillage. A strength of the model as tested is its ability to explain the variability in crop production, C inputs and SOC and N cycling over a wide range of soil, cropping and climatic conditions over periods from 6 to 61 years. For example, at the Breton site over 61 years, EPIC accounted for 69% of the variability in grain yields, 89% of the variability in C inputs and 91% of the variability in SOC content in the top 15 cm. Continued development is needed in understanding why it overpredicts at low SOC and underpredicts at high SOC. Possibilities now exist to connect the C and N cycling parts of EPIC to algorithms to describe denitrification as driven by C metabolism and oxygen availability. (c) 2005 Elsevier B.V. All rights reserved.
  • Authors:
    • Rochette, P.
    • Pattey, E.
    • Newlands, N.
    • McAllister, T. A.
    • McGinn, S. M.
    • Masse, D.
    • Lemke, R.
    • Helgason, B. L.
    • Gregorich, E. G.
    • Gibb, D. J.
    • Ellert, B. H.
    • Dyer, J. A.
    • Desjardins, R. L.
    • Bolinder, M.
    • Boehm, M.
    • Angers, D. A.
    • Janzen, H. H.
    • Smith, W.
    • VandenBygaart, A. J.
    • Wang, H.
  • Source: Canadian Journal of Soil Science
  • Volume: 86
  • Issue: 3
  • Year: 2006
  • Summary: Greenhouse gas emissions from farms can be suppressed in two ways: by curtailing the release of these gases (especially N2O and CH4), and by storing more carbon in soils, thereby removing atmospheric COT But most practices have multiple interactive effects on emissions throughout a farm. We describe an approach for identifying practices that best reduce net, whole-farm emissions. We propose to develop a "Virtual Farm", a series of interconnected algorithms that predict net emissions from flows of carbon, nitrogen, and energy. The Virtual Farm would consist of three elements: descriptors, which characterize the farm; algorithms, which calculate emissions from components of the farm; and an integrator, which links the algorithms to each other and the descriptors, generating whole-farm estimates. Ideally, the Virtual Farm will be: boundary-explicit, with single farms as the fundamental unit; adaptable to diverse farm types; modular in design; simple and transparent; dependent on minimal, attainable inputs; internally consistent; compatible with models developed elsewhere; and dynamic ("seeing" into the past and the future). The Virtual Farm would be constructed via two parallel streams - measurement and modeling - conducted iteratively. The understanding built into the Virtual Farm may eventually be applied to issues beyond greenhouse gas mitigation.
  • Authors:
    • France, J.
    • Wagner-Riddle, C.
    • Clark, K.
    • Kebreab, E.
  • Source: Canadian Journal of Animal Science
  • Volume: 86
  • Issue: 2
  • Year: 2006
  • Summary: Considerable evidence of climate change associated with emissions of greenhouse gases (GHG) has resulted in international efforts to reduce GHG emissions. The agriculture sector contributes about 8% of GHG emissions in Canada mostly through methane (CH4) and nitrous oxide (N2O). The objective of this paper was to compile an integrative review of CH4 and N2O emissions from livestock by taking a whole cycle approach from enteric fermentation to manure treatment and storage, and field application of manure. Basic microbial processes that result in CH4 production in the rumen and hindgut of animals were reviewed. An overview of CH4 and N2O production processes in manure, and controlling factors are presented. Most of the studies conducted in relation to enteric fermentation were in dairy and beef cattle. To date, research has focussed on GHG emissions from the stored manures of dairy, beef cattle and swine; therefore, we focus our review on these. Several methods used to measure GHG emissions from livestock and stored manure were reviewed. A comparison of methods showed that there were agreements between most of the techniques but some systematic differences were also observed. Additional studies with comprehensive comparisons of methodologies are needed in order to allow for comparison of results obtained from studies using contrasting methodologies. The need to standardize measurement methods and reporting to facilitate comparison of results and data integration was identified. Prediction equations are often used to calculate GHG emissions. Various types of mathematical approaches, such as statistical models, mechanistic models and estimates calculated from emission factors, and studies that compare various types of models are discussed herein. A lack of process-based models describing GHG emissions from manure during storage was identified. A brief description of mitigation strategies focussing on recent studies is given. Reduction in CH4 emissions from ruminants through the addition of fats in diets and the use of more starch was achieved and a transient beneficial effect of ionophores was reported. Grazing management and genetic selection also hold promise. Studies focussed on manure treatment options that have been suggested to reduce gas fluxes from manure storage, composting, anaerobic digestion (AD), diet manipulation, covers and solid-liquid separation, were reviewed. While some of these options have been shown to decrease GHG emissions from stored manure, different studies have obtained conflicting results, and additional research is needed to identify the most promising options. GHG emissions from pasture and croplands after manure application have been the subject of several experimental and modelling studies, but few of these have linked field emissions to diet manipulation or manure treatments. Further work focussing on the entire cycle of GHG formation from feed formulation, animal metabolism, excreta treatment and storage, to field application of manure needs to be conducted.
  • Authors:
    • Paustian, K.
    • Lokupitiya, E.
  • Source: Journal of Environmental Quality
  • Volume: 35
  • Year: 2006
  • Summary: Parties to the United Nations Framework Convention on Climate Change (UNFCCC) are required to submit national greenhouse gas (GHG) inventories, together with information on methods used in estimating their emissions. Currently agricultural activities contribute a significant portion (approximately 20%) of global anthropogenic GHG emissions, and agricultural soils have been identified as one of the main GHG source categories within the agricultural sector. However, compared to many other GHG sources, inventory methods for soils are relatively more complex and have been implemented only to varying degrees among member countries. This review summarizes and evaluates the methods used by Annex 1 countries in estimating CO2 and N2O emissions in agricultural soils. While most countries utilize the Intergovernmental Panel on Climate Change (IPCC) default methodology, several Annex 1 countries are developing more advanced methods that are tailored for specific country circumstances. Based on the latest national inventory reporting, about 56% of the Annex 1 countries use IPCC Tier 1 methods, about 26% use Tier 2 methods, and about 18% do not estimate or report N2O emissions from agricultural soils. More than 65% of the countries do not report CO2 emissions from the cultivation of mineral soils, organic soils, or liming, and only a handful of countries have used country-specific, Tier 3 methods. Tier 3 methods usually involve process-based models and detailed, geographically specific activity data. Such methods can provide more robust, accurate estimates of emissions and removals but require greater diligence in documentation, transparency, and uncertainty assessment to ensure comparability between countries. Availability of detailed, spatially explicit activity data is a major constraint to implementing higher tiered methods in many countries.