• Authors:
    • Chhabra, B. S.
    • Wang, Z. H.
    • Lemke, R.
    • Malhi, S. S.
  • Source: Soil & Tillage Research
  • Volume: 90
  • Issue: 1-2
  • Year: 2006
  • Summary: Management practices that simultaneously improve soil properties and yield are crucial to sustain high crop production and minimize detrimental impact on the environment. The objective of this study was to determine the influence of tillage and crop residue management on crop yield, N uptake and C removal in crop, soil organic C and N, inorganic N and aggregation, and nitrous oxide (N2O) emissions on a Gray Luvisol (Boralf) soil near Star City, Saskatchewan, Canada. The 4-year (1998-2001) field experiment was conducted with two tillage systems: no tillage (NT), and conventional tillage (CT); two levels of straw: straw retained (S), and straw removed (NS); and four rates of fertilizer N: 0, 40, 80, and 120 kg N ha-1, except no N to pea phase of the rotation. The plots were seeded to barley (Hordeum vulgare L.) in 1998, pea (Pisum sativum L.) in 1999, wheat (Triticum aestivum L.) in 2000 and canola (Brassica napus L.) in 2001. Tillage and straw treatments generally had no effect on crop yield during the first three years. But in 2001, NT produced 55, 32, and 20% greater canola seed, straw and chaff than CT, respectively, whereas straw retention increased seed and straw yield by 33 and 19% compared to straw removal. Seed, straw and chaff yield of canola increased with N rate up to 40 kg N ha-1, and root mass (0-15 cm depth) with N rate to 80 kg N ha-1. Amount of N uptake and C removed in wheat and canola generally increased with N rate, but tillage and straw management had no consistent effect. After four crop seasons, total organic C (TOC) and N (TN), light fraction organic matter (LFOM), C (LFC), and N (LFN) were generally greater with S than NS treatments. Tillage did not affect TOC and TN in soil, but LFOM, LFC, and LFN were greater or tended to be greater under NT than CT. There was no effect of tillage, straw and N fertilization on NH4-N in soil, but CT and S tended to have higher NO3-N concentration in 0-15 cm soil than NT and NS, respectively. Concentration of NO3-N increased substantially with N rate >=80 kg ha-1. The NT + S treatment had the lowest proportion (34%) of wind-erodible (12.7 mm) dry aggregates, compared to highest (50%) and lowest (18%) proportion of corresponding aggregates in CT + NS, indicating less potential for soil erosion when tillage was omitted and crop residues were retained. Amount of N lost as N2O was higher from N-fertilized than from zero-N plots, and it was substantially higher from N-applied CT plots than from N-applied NT plots. Retaining crop residues along with no-tillage improved soil properties and may also be better for the environment.
  • Authors:
    • McLauchlan, K.
  • Source: Ecosystems
  • Volume: 9
  • Issue: 8
  • Year: 2006
  • Summary: Since the domestication of plant and animal species around 10,000 years ago, cultivation and animal husbandry have been major components of global change. Agricultural activities such as tillage, fertilization, and biomass alteration lead to fundamental changes in the pools and fluxes of carbon (C), nitrogen (N), and phosphorus (P) that originally existed in native ecosystems. Land is often taken out of agricultural production for economic, social, or biological reasons, and the ability to predict the biogeochemical trajectory of this land is important to our understanding of ecosystem development and our projections of food security for the future. Tillage generally decreases soil organic matter (SOM) due to erosion and disruption of the physical, biochemical, and chemical mechanisms of SOM stabilization, but SOM can generally reaccumulate after the cessation of cultivation. The use of organic amendments causes increases in SOM on agricultural fields that can last for centuries to millennia after the termination of applications, although the locations that provide the organic amendments are concurrently depleted. The legacy of agriculture is therefore highly variable on decadal to millennial time scales and depends on the specific management practices that are followed during the agricultural period. State factors such as climate and parent material (particularly clay content and mineralogy) modify ecosystem processes such that they may be useful predictors of rates of postagricultural biogeochemical change. In addition to accurate biogeochemical budgets of postagricultural systems, ecosystem models that more explicitly incorporate mechanisms of SOM loss and formation with agricultural practices will be helpful. Developing this predictive capacity will aid in ecological restoration efforts and improve the management of modern agroecosystems as demands on agriculture become more pressing.
  • Authors:
    • McLaughlin, N. B.
    • Calder, W.
    • Welacky, T. W.
    • Tan, C. S.
    • Reynolds, W. D.
    • Drury, C. F.
  • Source: Soil Science Society of America Journal
  • Volume: 70
  • Issue: 2
  • Year: 2006
  • Summary: Innovative management practices are required to increase the efficiency of N fertilizer usage and to reduce nitrous oxide (N2O) and carbon dioxide (CO2) emissions from agricultural soils. The objectives of this study were to evaluate the feasibility of using conservation tillage and N fertilizer placement depth to reduce N2O and CO2 emissions associated with corn (Zea mays L.) production on clay loam soils in Eastern Canada. A 3-yr field study was established on a wheat (Triticum aestivum L.)-corn-soybean [Glycine max (L.) Merr.] rotation with each phase of the rotation present every year. Investigations were focused on the corn phase of the rotation. The tillage treatments following winter wheat included fall moldboard plow tillage (15 cm depth), fall zone-tillage (21 cm width, 15 cm depth), and no-tillage. The N placement treatments were "shallow" placement of sidedress N (2-cm depth) and "deep" placement of sidedress N (10-cm depth). Nitrous oxide emissions were measured 53 times and CO2 emissions were measured 43 times over three growing seasons using field-based sampling chambers. There was a significant tillage and N placement interaction on N2O emissions. Averaged over all three tillage systems and site-years, N2O emissions from shallow N placement (2.83 kg N ha-1 yr-1) were 26% lower than deep N placement (3.83 kg N ha-1 yr-1). The N2O emissions were similar among the tillage treatments when N was placed in the soil at a shallow depth. However, when N was placed deeper in the soil (10 cm), the 3-yr average N2O emissions from zone-tillage (2.98 kg N ha-1 yr-1) were 20% lower than from no-tillage (3.71 kg N ha-1 yr-1) and 38% lower than those from moldboard plow tillage (4.81 kg N ha-1 yr-1). Tillage type and N placement depth did not affect CO2 emissions (overall average = 5.80 Mg C ha-1 yr-1). Hence, zone-tillage and shallow N placement depth reduced N2O emissions without affecting CO2 emissions.
  • Authors:
    • Puurveen, H.
    • Kryzanowski, L. M.
    • Goddard, T. W.
    • Pattey, E.
    • Grant, R. F.
  • Source: Soil Science Society of America Journal
  • Volume: 70
  • Issue: 1
  • Year: 2006
  • Summary: The attribution of N2O emission factors to N inputs from chemical fertilizers requires an understanding of how those inputs affect the biological processes from which these emissions are generated. We propose a detailed model of soil N transformations as part of the ecosystem model ecosys for use in attributing N2O emission factors to fertilizer use. In this model, the key biological processes--mineralization, immobilization, nitrification, denitrification, root, and mycorrhizal uptake--controlling the generation of N2O were coupled with the key physical processes--convection, diffusion, volatilization, dissolution--controlling the transport of the gaseous reactants and products of these biological processes. Physical processes controlling gaseous transport and solubility caused large temporal variation in the generation and emission of N2O in the model. This variation limited the suitability of discontinuous surface flux chambers measurements used to test modeled N2O emissions. Continuous flux measurements using micrometeorological techniques were better suited to the temporal scales at which variation in N2O emission occurred and at which model testing needed to be conducted. In a temperate, humid climate, modeled N2O emissions rose nonlinearly with fertilizer application rate once this rate exceeded the crop and soil uptake capacities for added N. These capacities were partly determined by history of fertilizer use, so that the relationship between N2O emissions and current N inputs depended on earlier N inputs. A scheme is proposed in which N2O emission factors rise nonlinearly with fertilizer N inputs that exceed crop plus soil N uptake capacities.
  • Authors:
    • Trettin, C. C.
    • Bliss, N. B.
    • Keller, J. K.
    • Megonigal, J. P.
    • Bridgham, S. D.
  • Source: Wetlands
  • Volume: 26
  • Issue: 4
  • Year: 2006
  • Summary: We examine the carbon balance of North American wetlands by reviewing and synthesizing the published literature and soil databases. North American wetlands contain about 220 Pg C, most of which is in peat. They are a small to moderate carbon sink of about 49 Tg C yr(-1), although the uncertainty around this estimate is greater than 100%, with the largest unknown being the role of carbon sequestration by sedimentation in freshwater mineral-soil wetlands. We estimate that North American wetlands emit 9 Tg methane (CH4) yr(-1); however, the uncertainty of this estimate is also greater than 100%. With the exception of estuarine wetlands, CH4 emissions from wetlands may largely offset any positive benefits of carbon sequestration in soils and plants in terms of climate forcing. Historically, the destruction of wetlands through land-use changes has had the largest effects on the carbon fluxes and consequent radiative forcing of North American wetlands. The primary effects have been a reduction in their ability to sequester carbon (a small to moderate increase in radiative forcing), oxidation of their soil carbon reserves upon drainage (a small increase in radiative forcing), and reduction in CH4 emissions (a small to large decrease in radiative forcing). It is uncertain how global changes will affect the carbon pools and fluxes of North American wetlands. We will not be able to predict accurately the role of wetlands as potential positive or negative feedbacks to anthropogenic global change without knowing the integrative effects of changes in temperature, precipitation, atmospheric carbon dioxide concentrations, and atmospheric deposition of nitrogen and sulfur on the carbon balance of North American wetlands.
  • Authors:
    • Janzen, H. H.
    • Angers, D. A.
    • Gregorich, E. G.
    • VandenBygaart, A. J.
    • Bolinder, M. A.
  • Source: Canadian Journal of Soil Science
  • Volume: 86
  • Issue: 3
  • Year: 2006
  • Summary: Modelling soil organic carbon (SOC) stock changes in agroecosystems can be performed with different approaches depending on objectives and available data. Our objective in this paper is to describe a scheme for developing a dynamic SOC algorithm for calculating net greenhouse gas emissions from Canadian farms as a function of management and local conditions. Our approach is flexible and emphasizes ease of use and the integration of available knowledge. Using this approach, we assessed the performance of several SOC models having two or more compartments for some common agroecosystems in Canada. Analysis of long-term data for conventional management practices at different sites (n = 36) in Canada, including recent model applications in the literature on some of those data, indicated that the results obtained with two-compartment models, such as the Introductory Carbon Balance Model (ICBM) and Modified Woodruff Model (MWM), yielded results comparable to those of a multi-compartment model (CENTURY). The analysis also showed that a model such as ICBM need stuning to be applied to management and conditions across Canada. Two-compartment models programmable in a simple spreadsheet format, though they may not supplant more complex models in allapplications, offer advantages of simplicity and transparency in whole-farm analyses of greenhouse gas emissions. Key words: Virtual Farm, soil organic carbon, soil disturbance, C inputs, Introductory Carbon Balance Model (ICBM), CENTURY, Modified Woodruff Model (MWM).
  • Authors:
    • Derksen, D.
    • May, W.
    • Johnston, A.
    • Clayton, G.
    • Lafond, G.
    • Stevenson, F.
  • Source: Canadian Journal of Plant Science
  • Volume: 86
  • Issue: 2
  • Year: 2006
  • Summary: Surface residues and standing stubble protect soil against erosion and mitigate against crop water deficits by conserving additional moisture. However, residues and stubble can also present a dilemma for producers practising no-till in terms of nitrogen (N) fertilizer management and row spacing. The objective of this research was to determine how row spacing, N management using urea and two rates of post-emergent herbicide (66 and 100% of recommended) affect spring wheat establishment and plant development. The study was conducted using a no-till system and a canola-spring wheat cropping system at three locations over a 3-yr period. The N management and row spacing treatments were (1) 23-cm row spacing with fall banded N on 30 cm; (2) 23-cm row spacing with spring banded N on 30 cm; (3) 30-cm row spacing with the N side-banded; (4) 23-cm row spacing with the N side-banded; and (5) sweep on 23-cm spacing with seed and fertilizer scattered over a 20-cm width. Herbicide rates did not affect wheat development. Planting depth was greater for the sweep treatment, but only by 6 mm. Plant densities were at the low end of the optimal range of 200-250 plants m -2 for all treatments and were least for the 30 cm row spacing. Average frequencies for tillers T0, T1, T2 and T3 were 20, 81 61 and 10%, respectively. Fall and spring band treatments resulted in lower tiller frequencies than the sweep treatment, with intermediate levels for the side-band treatments. Tiller frequencies were identical between the 23-cm and 30-cm row spacings with N side-banded. Greater tiller frequencies for the sweep treatment likely resulted from the greater spread of seed, reducing inter-plant competition and closer proximity of the seed to fertilizer N. Spike density was not affected by N management. Expected spike density, calculated from tiller frequency and plant density data, was within 1% of the actual spikes recorded, when averaged over treatments. This means that tiller frequencies at the 5 to 5.5 leaf stage are a good predictor of expected spike density. Wider row spacings did not affect plant and tiller development but applying N fertilizer at time of seeding provided better spring wheat tiller development.
  • Authors:
    • Solberg, E. D.
    • Nyborg, M.
    • Malhi, S. S.
    • Izaurralde, R. C.
    • Jakas, M. C. Quiroga
  • Source: Agronomy Journal
  • Volume: 98
  • Issue: 5
  • Year: 2006
  • Summary: Field experiments were conducted from 1991 to 1995 at Josephburg (Orthic Black Chernozem, Typic Cryoboroll) and Cooking Lake (Orthic Gray Luvisol, Typic Cryoboralf), Alberta, to determine the impact of topsoil removal on selected soil properties, N-mineralization potential, and crop yield, and the effectiveness of various amendments for restoring the productivity of eroded soils. The simulated-erosion levels were established in the autumn of 1990 by removing 20 cm of topsoil in 5-cm depth increments. The four amendments were: control, addition of 5 cm of topsoil, fertilizers to supply 100 kg N ha(-1) and 20 kg P ha(-1), and cattle manure at 75 Mg ha(-1). Topsoil and manure were applied once in the autumn of 1990, while fertilizers were applied annually from 1991 to 1995. Available N and P; total C, N, and P; and N-mineralization potential decreased, while bulk density increased with increasing depth of topsoil removal. Tiller number, plant height, spike density, thousand-kernel weight, and leaf area index decreased with simulated erosion. Grain yield reductions due to simulated soil erosion were either linear or curvilinear functions of nutrient removal. Application of N and P fertilizers and manure improved grain yield and reduced the impact of yield loss due to erosion. Return of 5 cm of topsoil also increased grain yield, but to a lesser extent than manure or fertilizers. Grain yields were maximized when fertilizers were also applied to organic amendment treatments. Our findings suggest the importance of integrated use of organic amendments and chemical fertilizers for best crop yields on severely eroded soils.
  • Authors:
    • Karamanos, R. E.
    • Malhi, S. S.
  • Source: Canadian Journal of Plant Science
  • Volume: 86
  • Issue: 3
  • Year: 2006
  • Summary: Deficiency of copper (Cu) in Canadian prairie soils is not widespread, but whenever it occurs it can cause a drastic reduction in seed yield and quality of most cereals, especially wheat. Field experiments conducted in western Canada indicated that broadcast-incorporation of granular Cu fertilizers prior to seeding at 3-5.6 kg Cu ha(-1) was usually sufficient to prevent Cu deficiency in wheat, and improve seed yield and quality. At lower rates ( (barley, alfalfa) > (timothy seed, oats, corn) > (peas, clovers) > (canola, rye, forage grasses). Stem melanosis in wheat was associated with deficiency of Cu in soil, and the disease was reduced substantially with Cu application. A high level of available P in soil was observed to induce/increase severity of Cu deficiency in wheat. Soil analysis for diethylene triamine pentacetic acid- (DTPA) extractable Cu in soil can be used as a good diagnostic tool to predict Cu deficiency, but there was a poor relationship between total Cu concentration in shoots and the degree of Cu deficiency in crops. Application of Cu fertilizers to wheat on Cu-deficient soils also generally improved seed quality.
  • Authors:
    • Mason, H. E.
    • Spaner, D.
  • Source: Canadian Journal of Plant Science
  • Volume: 86
  • Issue: 2
  • Year: 2006
  • Summary: Wheat (Triticum aestivum L.) is the world's most widely grown crop, cultivated in over 115 nations. Organic agriculture, a production system based on reducing external inputs in order to promote ecosystem health, can be defined as a system that prohibits the use of synthetic fertilizers, chemical pesticides and genetically modified organisms. Organic agriculture is increasing in popularity, with a 60% increase in the global acreage of organically managed land from the year 2000 to 2004. Constraints that may be associated with organic grain production include reduced yields due to soil nutrient deficiencies and competition from weeds. Global wheat breeding efforts over the past 50 yr have concentrated on improving yield and quality parameters; in Canada, disease resistance and grain quality have been major foci. Wheat varieties selected before the advent of chemical fertilizers and pesticides may perform differently in organic, low-input management systems than in conventional, high-input systems. Height, early-season growth, tillering capacity, and leaf area are plant traits that may confer competitive ability in wheat grown in organic systems. Wheat root characteristics may also affect competitive ability, especially in low-input systems, and more research in this area is needed. The identification of a competitive crop ideotype may assist wheat breeders in the development of competitive wheat varieties. Wheat varieties with superior performance in low-input systems, and/or increased competitive ability against weeds, could assist organic producers in overcoming some of the constraints associated with organic wheat production.