• Authors:
    • Clayton, G. W.
    • Harker, K. N.
    • Soon, Y. K.
  • Source: Soil Science Society of America Journal
  • Volume: 68
  • Issue: 2
  • Year: 2004
  • Summary: We evaluated weed competition effects on the N economy of field pea (Pisum sativum L.) and the subsequent crop to address the paucity of such information. Plots were seeded to pea, canola (Brassica napus L.) and barley (Hordeum vulgare L.) in 1997 and 1998. Weeds, augmented by cross-seeding experimental plots with oat (Avena sativa L.), were removed with herbicides one and four weeks after crop emergence (WAE). The subsequent barley crop received 0 or 6 g N m(-2). Mean percentage of N derived from the atmosphere (%Ndfa) for the 2 yr, estimated by N-15 isotopic dilution, was 81% for the 4-WAE treatment and 51% for the 1-WAE treatment, indicating that a pea plant subjected to greater weed competition derived more of its N from symbiotic fixation. Total N fixed by pea was not affected by the time of weed removal, however, and total N uptake and seed yield were greater with early weed removal due to less competition for soil N. Early weed removal resulted in net N export in pea seeds (because of higher production) while later weed removal resulted in gains of 1.1 to 1.3 g N m(-2). However, time of weed removal during pea cultivation had no effect on the yield or N uptake of the subsequent barley crop. Higher barley yield and N uptake following pea than following barley were mostly the result of greater N availability. Nitrogen fertilization benefited the subsequent barley regardless of preceding crop type.
  • Authors:
    • Blackshaw, R. E.
    • O'Donovan, J. T.
    • Clayton, G. W.
    • Harker, K. N.
    • Stevenson, F. C.
  • Source: Weed Technology
  • Volume: 18
  • Issue: 4
  • Year: 2004
  • Summary: Herbicide-resistant canola dominates the canola market in Canada. A multiyear field experiment was conducted at three locations to investigate the effect of time of weed removal (two-, four-, or six-leaf canola) and herbicide rate (50 or 100% recommended) in three herbicide-resistant canola systems. Weeds were controlled in glufosinate-resistant canola (GLU) with glufosinate, in glyphosate-resistant canola (GLY) with glyphosate, and in imidazolinone-resistant canola (IMI) with a 50:50 mixture of imazamox and imazethapyr. Canola yields were similar among the three canola cultivar-herbicide systems. Yields were not influenced by 50 vs. 100% herbicide rates. Timing of weed removal had the greatest effect on canola yield, with weed removal at the four-leaf stage giving the highest yields in most cases. Percent dockage was often greater for GLU and IMI than for GLY. In comparison with the other treatments, dockage levels doubled for GLU after application at 50% herbicide rates. The consistency of monocot weed control was usually greater for GLY than for GLU or IMI systems. However, weed biomass data revealed no differences in dicot weed control consistency between IMI and GLY systems. Greater dockage and weed biomass variability after weed removal at the six-leaf stage or after low herbicide rates suggests higher weed seed production, which could constrain the adoption of integrated weed management practices in subsequent years.
  • Authors:
    • Laslo, J. J.
    • Meers, S.
    • Hall, L. M.
    • Beckie, H. J.
    • Stevenson, F. C.
  • Source: Weed Technology
  • Volume: 18
  • Issue: 3
  • Year: 2004
  • Summary: A 3-yr study was conducted in Wheatland County, Alberta to determine if agronomic practices of growers influenced the occurrence of herbicide resistance in wild oat. Wild oat seeds were collected in 33 fields in 1997 and in 31 fields in each of 1998 and 1999 (one field per grower). Seedlings were screened for resistance to two acetyl-CoA carboxylase (ACCase) inhibitors, imazamethabenz, an acetolactate synthase (ALS) inhibitor, and triallate, a thiocarbamate herbicide. A questionnaire on herbicide resistance awareness and management practices was completed by each grower. Both ACCase and ALS inhibitor resistance in wild oat were linked to a lack of crop rotation diversity. In addition, ALS inhibitor-resistant wild oat was associated with conservation-tillage systems and recent use of herbicides with that mode of action. Results of this study suggest that timely tillage and inclusion of fall-seeded and perennial forage crops in rotations will effectively slow the selection of resistance in this grass species.
  • Authors:
    • Turvey, C. G.
    • Kay, B. D.
    • Joseph, S.
    • Weersink, A.
  • Source: CAFRI: Current Agriculture, Food and Resource Issues
  • Volume: 4
  • Year: 2003
  • Summary: The objective of the 1997 Kyoto agreement was to limit greenhouse gas (GHG) emissions among signatory countries and thereby slow global warming. Under the agreement, Canada has committed itself to reduce GHGs over the next decade by 6 percent from estimated 1990 levels. Debate has now begun on the appropriate government policies that will induce the desired GHG reductions. Regulations could be in the form of direct controls or economic incentives, such as a subsidy/tax system or an emission trading system. The success of the U.S. emission market for SO2 (Schmalenseeet al., 1998) has generated growing interest in the use of a similar market mechanism for carbon (Holmes and Friedman, 2000). The existence of a carbon credit market presents the agricultural sector with another potential revenue source (Sandor and Skees, 1999). While agriculture contributes approximately 10 percent of Canada’s greenhouse gas emissions, it also has the potential to sequester carbon through strategies such as zero tillage, reduced summer fallow and improved grazing. These sequestration activities could be incorporated into an emission trading system and create a “carbon credit” for each unit of CO2 that is removed from the atmosphere. Firms with high emission reduction costs could then buy these credits rather than bear the large abatement costs associated with reducing their GHG emission levels. The perception is that the marginal cost of abatement for agriculture is less than that for other sectors (McCarl and Schneider, 2000). Thus, farmers may be able to profit by selling credits for activities that sequester carbon. An example of such a transaction was the purchase of carbon credits from Iowa farmers who adopted no-till by a consortium of Canadian energy companies (GEMCO) (Lessiter, 1999). Whether the development of a carbon credit market will affect the management decisions of an Ontario crop farmer is the focus of this study.
  • Authors:
    • Nair, V. D.
    • Nair, P. K. R.
  • Source: The Potential of U.S. Forest Soils to Sequester Carbon and Mitigate the Greenhouse Effect
  • Year: 2003
  • Summary: Agroforestry is a new concept of land management, especially in North America; therefore quantitative data are rare if not nonexistent on most aspects of it. Carbon sequestration potential of agroforestry systems is one such little-studied area. In the discussion on C storage potential of any land-use system, it is important that the system characteristics and processes governing their functioning are understood adequately. Since such basic information about agroforestry systems is not widely known, in this chapter we will first present background information on the key concepts of agroforestry and major types of agroforestry systems in North America. We then examine the C sequestration potential of agroforestry systems and discuss management considerations and research needs for exploiting the potential.
  • Authors:
    • Beauchamp, E. G.
    • Tenuta, M.
  • Source: Canadian Journal of Soil Science
  • Volume: 83
  • Issue: 5
  • Year: 2003
  • Summary: One field and two laboratory experiments were conducted to determine the relative magnitude and pattern of N2O production from several granular N fertilizers including urea, ammonium nitrate, calcium nitrate, ammonium sulfate and, in a laboratory experiment, monoammonium and diammonium phosphates. Several parameters, in particular soil water content, were studied for their roles in N2O production with these fertilizers. The field experiment was conducted at the Elora Research Station (20 km north of Guelph) on Conestoga silt loam during July on a site previously cropped to barley. Three methods were employed to assess N2O production following N fertilizer treatments in the field experiment, viz., soil cover, soil core and profile distribution. The data with each method revealed that incorporated urea produced the greatest quantity of N2O especially in the first few days following application. Shortly after urea application and incorporation (10 cm), N2O was detected at a depth of 50 cm indicating gas produced in the tilled layer was transported to lower depths. Data obtained with the intact core method showed that nitrification preceeded denitrification as the source of N2O produced during a wetting event as air-filled porosity decreased from 65% to less than 50%, respectively. The laboratory experiments showed that under aerobic conditions N2O production was generally greater with urea than the other N fertilizers. The greater production of N2O with urea was associated with NO2-accumulation. In the second laboratory experiment, saturating the soil following 14 d of aerobic incubation showed enhanced N2O production with ammonium phosphate fertilizers. Our findings indicate refinement of methods to predict N2O emissions based on N fertilizer source use and moisture can reduce uncertainties in national estimates of N2O emissions from agricultural soils.
  • Authors:
    • Angers, D. A.
    • Gregorich, E. G.
    • VandenBygaart, A. J.
  • Source: Canadian Journal of Soil Science
  • Volume: 83
  • Issue: 4
  • Year: 2003
  • Summary: To fulfill commitments under the Kyoto Protocol, Canada is required to provide verifiable estimates and uncertainties for soil organic carbon (SOC) stocks, and for changes in those stocks over time. Estimates and uncertainties for agricultural soils can be derived from long-term studies that have measured differences in SOC between different management practices. We compiled published data from long-term studies in Canada to assess the effect of agricultural management on SOC. A total of 62 studies were compiled, in which the difference in SOC was determined for conversion from native land to cropland, and for different tillage, crop rotation and fertilizer management practices. There was a loss of 24 ± 6% of the SOC after native land was converted to agricultural land. No-till (NT) increased the storage of SOC in western Canada by 2.9 ± 1.3 Mg ha–1; however, in eastern Canada conversion to NT did not increase SOC. In general, the potential to store SOC when NT was adopted decreased with increasing background levels of SOC. Using no-tillage, reducing summer fallow, including hay in rotation with wheat (Triticum aestivum L.), plowing green manures into the soil, and applying N and organic fertilizers were the practices that tended to show the most consistent increases in SOC storage. By relating treatment SOC levels to those in the control treatments, SOC stock change factors and their levels of uncertainty were derived for use in empirical models, such as the United Nations Intergovernmental Panel on Climate Change (IPCC) Guidelines model for C stock changes. However, we must be careful when attempting to extrapolate research plot data to farmers fields since the history of soil and crop management has a significant influence on existing and future SOC stocks.
  • Authors:
    • Lal, R.
  • Source: Critical Reviews in Plant Sciences
  • Volume: 22
  • Issue: 2
  • Year: 2003
  • Summary: An increase in atmospheric concentration of CO2 from 280 ppmv in 1750 to 367 ppmv in 1999 is attributed to emissions from fossil fuel combustion estimated at 270 +/- 30 Pg C and land use change at 136 +/- 55 Pg. Of the emissions from land use change, 78 +/- 12 Pg is estimated from depletion of soil organic carbon (SOC) pool. Most agricultural soils have lost 50 to 70% of their original SOC pool, and the depletion is exacerbated by further soil degradation and desertification. The restoration of degraded soils, conversion of agriculturally marginal lands to appropriate land use, and the adoption of recommended management practices on agricultural soils can reverse degradative trends and lead to SOC sequestration. Technological options for SOC sequestration on agricultural soils include adoption of conservation tillage, use of manures, and compost as per integrated nutrient management and precision fanning strategies, conversion of monoculture to complex diverse cropping systems, meadow-based rotations and winter cover crops, and establishing perennial vegetation on contours and steep slopes. The global potential of SOC sequestration and restoration of degraded/desertified soils is estimated at 0.6 to 1.2 Pg C/y for about 50 years with a cumulative sink capacity of 30 to 60 Pg. The SOC sequestration is a cost-effective strategy of mitigating the climate change during the first 2 to 3 decades of the 21(st) century. While improving soil quality, biomass productivity and enhanced environment quality, the strategy of SOC sequestration also buys us time during which the non-carbon fuel alternatives can take effect.
  • Authors:
    • Liu, A.
    • Hamel, C.
    • Madramootoo, C.
    • Elmi, A.
  • Source: Biology and Fertility of Soils
  • Volume: 38
  • Issue: 6
  • Year: 2003
  • Summary: There is a growing interest in the adoption of conservation tillage systems [no-till (NT) and reduced tillage (RT)] as alternatives to conventional tillage (CT) systems. A 2-year study was conducted to investigate possible environmental consequences of three tillage systems on a 2.4-ha field located at Macdonald Research Farm, McGill University, Montreal. The soil was a sandy loam (0.5 m depth) underlain by a clay layer. Treatments consisted of a factorial combination of CT, RT, and NT with the presence or absence of crop residue. Soil NO 3 --N concentrations tended to be lower in RT than NT and CT tillage treatments. Denitrification and N 2O emissions were similar among tillage systems. Contrary to the popular assumption that denitrification is limited to the uppermost soil layer (0–0.15 m), large rates of N 2O production were measured in the subsurface (0.15–0.45 m) soil, suggesting that a significant portion of produced N 2O may be missed if only soil surface gas flux measurements are made. The N 2O mole fraction (N 2O:N 2O+N 2) was higher in the drier season of 1999 under CT than in 2000, with the ratio occasionally exceeding 1.0 in some soil layers. Dissolved organic C concentrations remained high in all soil depths sampled, but were not affected by tillage system .
  • Authors:
    • Pattey, E.
    • Grant, R. F.
  • Source: Soil Biology and Biochemistry
  • Volume: 35
  • Issue: 2
  • Year: 2003