• Authors:
    • Aitken, S. N.
    • Yanchuk, A. D.
    • Gapare, W. J.
  • Source: Conservation Genetics
  • Volume: 9
  • Issue: 2
  • Year: 2008
  • Summary: In previous studies we reported that while core populations of Sitka spruce [Picea sitchensis (Bong.) Carr] have little within-population genetic structure, peripheral populations are strongly spatially structured at distances up to 500 m. Here we explore the implications of this difference in structure on ex situ gene conservation collections and estimates of genetic diversity from research collections. We test the effects of varying the number of individuals sampled and the total area they are sampled across on capture of neutral genetic variation in collections from core, continuous versus peripheral, disjunct populations. Bivariate response surface analysis of genetic marker data for eight sequence tagged site loci from core and peripheral populations suggest that a population sample from 150 trees covering at least 225 ha would be adequate for capturing 95% of the genetic diversity (as measured by allelic richness or expected heterozygosity) in core populations. However, a larger sample of 180 individuals from an area of at least 324 ha is needed in peripheral populations to capture the same proportion of standing variation because of stronger within-population spatial genetic structure. Standard population sampling protocols for estimating among and within-population genetic diversity would significantly underestimate the within-population allelic richness and expected heterozygosity of peripheral but not core populations, potentially leading to poor representation of genetic variation in peripheral populations as well as erroneous conclusions about their genetic impoverishment.
  • Authors:
    • Blackshaw, R. E.
    • Johnson, E. N.
    • Beckie, H. J.
    • Gan, Y.
  • Source: Canadian Journal of Plant Science
  • Volume: 88
  • Issue: 2
  • Year: 2008
  • Summary: Competitive crops or cultivars can be an important component of integrated weed management systems. A study was conducted from 2003 to 2006 at four sites across semiarid prairie ecoregions in Saskatchewan and Alberta to investigate the productivity and quality of canola (Brassica napus L.) and mustard cultivars under weed competition. Four open-pollinated canola cultivars, four hybrid canola cultivars, two canola-quality mustard and two oriental mustard cultivars [Brassica juncea (L.) Czern. & Coss.], and two yellow mustard (Sinapis alba L.) cultivars were grown under weedy and weed-free conditions. When combined across site-years, crop aboveground biomass at maturity and seed yield were reduced by weed interference, except for yellow and oriental mustard. However, seed oil and protein content of cultivars were not affected by weed competition. Among crop types, yellow and oriental mustard were best able to maintain biomass and seed yield under weed interference, followed in decreasing order of competitiveness by hybrid and open-pollinated canola, then canola-quality mustard.
  • Authors:
    • Brenzil, C. A.
    • Hall, L. M.
    • Thomas, A. G.
    • Leeson,J. Y.
    • Beckie, H. J.
  • Source: Weed Technology
  • Volume: 22
  • Issue: 4
  • Year: 2008
  • Summary: Agricultural practices, other than herbicide use, can affect the rate of evolution of herbicide resistance in weeds. This study examined associations of farm management practices with the occurrence of herbicide (acetyl-CoA carboxylase or acetolactate synthase inhibitor)-resistant weeds, based upon a multi-year (2001 to 2003) random Survey of 370 fields/growers from the Canadian Prairies. Herbicide-resistant weeds Occurred in one-quarter of the surveyed fields. The primary herbicide-resistant weed species was wild oat, with lesser occurrence of green foxtail, kochia, common chickweed, spiny sowthistle, and redroot pigweed. The risk of weed resistance was greatest in fields with cereal-based rotations and least in fields with forage crops, fallow, or where three or more crop types were grown. Weed resistance risk also was greatest in conservation-tillage systems and particularly low soil disturbance no-tillage, possibly due to greater herbicide use or weed seed bank turnover. Large farms (> 400 ha) had a greater risk of weed resistance than smaller farms, although the reason for this association Was unclear. The results of this study identify cropping system diversity as the foundation of proactive weed resistance management.
  • Authors:
    • Weiss, M. J.
    • Pike, K. S.
    • Buntin, G. D.
    • Webster, J. A.
  • Source: Handbook of small grain insects
  • Year: 2007
  • Summary: This handbook is designed primarily for the practitioners of integrated pest management programmes in small grains, growers, crop consultants, extension agents, and company agronomists and sales representatives. Its primary objective is to provide fundamental and useful information about managing (through cultural, plant resistance, biological and chemical methods) small grain insects throughout the United States and Canada. Although it focuses on insect pests of small grains, noninsect pests (e.g. mites) also are covered. Crops covered in this handbook are wheat, barley, oats, rye and triticale, with an emphasis on wheat. The first three sections provide information about small grains and their production, principles and practices of small grain insect management, and an overview of the pest injury to small grains by insects, weeds, and plant pathogens. The remainder of the handbook is devoted to discussions of insect and mite pests of small grains and to beneficial organisms, including insect pathogens, parasitoids and predators.
  • Authors:
    • Menzies, J. G.
    • Haber, S. M.
    • Fetch, T. G.,Jr.
    • Chong, J.
    • Brown, P. D.
    • Duguid, S. D.
    • Fetch, J. W. M.
    • Ames, N.
    • Noll, J.
    • Aung, T.
    • Stadnyk, K. D.
  • Source: Canadian Journal of Plane Science
  • Volume: 87
  • Issue: 3
  • Year: 2007
  • Summary: Leggett is the first oat ( Avena sativa L.) cultivar released in western Canada carrying the crown rust resistance gene Pc94. Leggett carries the crown rust resistance combination Pc68 and Pc94, which provides good resistance to the crown rust populations currently present on the eastern Canadian Prairies. As a result of the presence of Pc94 providing resistance to oat crown rust, this line should exhibit excellent yield stability in the rust-prone regions of the prairies. Leggett has very good resistance to loose and covered smut, resistance to the prevalent races of oat stem rust other than NA67, but poor tolerance to barley yellow dwarf virus (BYDV). Leggett has kernel characteristics suited to milling end uses, with high test weight and 1000-kernel weight and high percent plump kernels. The beta-glucan content of Leggett is equal to or higher than that of the checks, making it a desirable milling quality cultivar.
  • Authors:
    • Emery, R.
    • Maxwell, C.
    • Manns, H.
  • Source: Soil & Tillage Research
  • Volume: 96
  • Issue: 1/2
  • Year: 2007
  • Summary: The unique capacity of fungi to efficiently sequester carbon in aerobic conditions, presents a way to maximize OC gain in agricultural systems. Oat ( Avena sativa) was planted in the temperate climate of southern Ontario, Canada to study factors affecting soil organic carbon (OC). The plots varied with initial OC from 25 to 68 g kg -1 or with ground cover of differing decomposability (alfalfa ( Medicago sativa) growing from seed, dried oat straw, dried hay and compost) on high OC soil (60-70 g kg -1). The soil was analysed for correlation of changes in soil aggregation, moisture, OC, fungal hyphal number and length and distribution of organic matter by mass and OC in density fractions within the growing season. At harvest, soil OC and moisture were increased only in plots with ground cover. Total hyphal length was not significantly different with ground cover treatment at harvest, and did not correlate with soil aggregation and soil OC. However, the number of hyphae with >5 m diameter (primarily mycorrhizal fungi) correlated with % OC in ground cover plots while the number of hyphae
  • Authors:
    • Huang, H.
    • Blackshaw, R.
    • Mover, J.
  • Source: Canadian Journal of Plant Science
  • Volume: 87
  • Issue: 4
  • Year: 2007
  • Summary: There is a renewed interest, especially among organic growers, in using either white sweetclover ( Melilotus alba Desr.) or yellow sweetclover [ M. officinalis (L.) Lam.] as cover crops. Sweetclover cultivars and tillage practices have changed since these crops were widely used as cover crops in the first half of the 20th century. Experiments were initiated in 1999, 2000, and 2002 to compare the effect of high- and low-coumarin cultivars and crop termination methods on weed suppression, available soil N, moisture conservation and following crop yield. Weed suppression was usually more effective when sweetclover residues were left on the surface than when removed as hay. Sweetclover termination at 70% bloom was often more effective in suppressing weeds than termination at the bud stage. In the summer and fall after termination, surface residues of Yukon, a high-coumarin and drought-tolerant cultivar, reduced lamb's-quarters ( Chenopodium album L.) density by >80% compared with the no sweetclover check and essentially eliminated flixweed [ Descurainia sophia (L). Webo]. In the following spring, Yukon reduced kochia [ Kochia scoparia (L.) Schrad.] density by >80% and wild oat ( Avena fatua L.) biomass by >30% compared with the no sweetclover check. There was no difference in available N for a following crop between treatments with surface residue and cultivated fallow. Available soil moisture was about 10 mm less after the highest yielding sweetclover cultivars than after cultivated fallow, but subsequent wheat yield was not reduced. Maximum wheat yields were obtained after Yukon and Arctic sweetclover were grown as cover crops. It may be possible for organic growers to manage weeds with sweetclover in a reduced tillage system that leaves most of the plant residues on the soil surface.
  • Authors:
    • May, W. E.
    • Brandt, S. A.
    • Lafond, G. P.
    • Holzapfel, C. B.
    • Johnston, A. M.
  • Source: Canadian Journal of Plant Science
  • Volume: 87
  • Issue: 2
  • Year: 2007
  • Summary: Delaying nitrogen (N) applications into the growing season as a risk management tool is a concept that has received considerable attention in recent years. A 3-yr field study with spring wheat ( Triticum aestivum L.) and canola ( Brassica napus L.) was conducted at two Saskatchewan locations, Indian Head and Scott. The effects of postponing N applications for up to 30 d after seeding and several application methods were evaluated against mid-row banded urea at seeding. Liquid urea ammonium-nitrate (UAN) was applied at four separate times relative to seeding, either as an in-soil coulter band or a surface band. The surface band applications were applied either with or without the addition of 5% ammonium thiosulphate (ATS), a potential urease inhibitor. The dependent variables considered included plant density and grain yield for both crops, and grain protein in wheat. The only effect on plant density occurred in canola, where the post-seeding coulter applications slightly reduced stands compared with the other treatments. Postponing N fertilization for up to 30 d after seeding compared with N fertilization at seeding did not affect the yield of canola or protein in spring wheat, but reduced the yield of spring wheat at Indian Head in 2003, which was a very dry growing season. The coulter applications only showed a slight advantage over the surface band applications. For the surface band applications, the addition of 5% ATS did not provide a noticeable advantage over UAN alone. Canola appeared to be less sensitive to post-seeding applications than spring wheat. Deferring the entire amount of fertilizer N into the growing season appears to be a viable option but it is not without risk, especially when dry conditions are encountered.
  • Authors:
    • Warland, J.
    • von Bertoldi, P.
    • Parkin, G.
    • Jayasundara, S.
    • Barbeau, J.
    • Lee, I.
    • McLaughlin, N. L.
    • Furon, A.
    • Wagner-Riddle, C.
  • Source: Global Change Biology
  • Volume: 13
  • Issue: 8
  • Year: 2007
  • Summary: No-tillage (NT), a practice that has been shown to increase carbon sequestration in soils, has resulted in contradictory effects on nitrous oxide (N2O) emissions. Moreover, it is not clear how mitigation practices for N2O emission reduction, such as applying nitrogen (N) fertilizer according to soil N reserves and matching the time of application to crop uptake, interact with NT practices. N2O fluxes from two management systems [conventional (CP), and best management practices: NT + reduced fertilizer (BMP)] applied to a corn (Zea mays L.), soybean (Glycine max L.), winter-wheat (Triticum aestivum L.) rotation in Ontario, Canada, were measured from January 2000 to April 2005, using a micrometeorological method. The superimposition of interannual variability of weather and management resulted in mean monthly N2O fluxes ranging from - 1.9 to 61.3 g N ha(-1) day(-1). Mean annual N2O emissions over the 5-year period decreased significantly by 0.79 from 2.19 kg N ha(-1) for CP to 1.41 kg N ha(-1) for BMP. Growing season (May-October) N2O emissions were reduced on average by 0.16 kg N ha(-1) (20% of total reduction), and this decrease only occurred in the corn year of the rotation. Nongrowing season (November-April) emissions, comprised between 30% and 90% of the annual emissions, mostly due to increased N2O fluxes during soil thawing. These emissions were well correlated (r(2) = 0.90) to the accumulated degree-hours below 0 degrees C at 5 cm depth, a measure of duration and intensity of soil freezing. Soil management in BMP (NT) significantly reduced N2O emissions during thaw (80% of total reduction) by reducing soil freezing due to the insulating effects of the larger snow cover plus corn and wheat residue during winter. In conclusion, significant reductions in net greenhouse gas emissions can be obtained when NT is combined with a strategy that matches N application rate and timing to crop needs.
  • Authors:
    • Six, J.
    • West, T. O.
  • Source: Climatic Change
  • Volume: 80
  • Issue: 1
  • Year: 2007
  • Summary: Rates of soil C sequestration have previously been estimated for a number of different land management activities, and these estimates continue to improve as more data become available. The time over which active sequestration occurs may be referred to as the sequestration duration. Integrating soil C sequestration rates with durations provides estimates of potential change in soil C capacity and more accurate estimates of the potential to sequester C. In agronomic systems, changing from conventional plow tillage to no-till can increase soil C by an estimated 16 ± 3%, whereas increasing rotation intensity can increase soil C by an estimated 6 ± 3%. The increase in soil C following a change in rotation intensity, however, may occur over a slightly longer period (26 yr) than that for tillage cessation (21 yr). Sequestration strategies for grasslands have, on average, longer sequestration durations (33 yr) than for croplands. Estimates for sequestration rates and durations are mean values and can differ greatly between individual sites and management practices. As the annual sequestration rate declines over the sequestration duration period, soil C approaches a new steady state. Sequestration duration is synonymous with the time to which soil C steady state is reached. However, soils could potentially sequester additional C following additional changes in management until the maximum soil C capacity, or soil C saturation, is achieved. Carbon saturation of the soil mineral fraction is not well understood, nor is it readily evident. We provide evidence of soil C saturation and we discuss how the steady state C level and the level of soil C saturation together influence the rate and duration of C sequestration associated with changes in land management.