• Authors:
    • Bakken ,L. R.
    • Dörsch,P.
    • Holtan-Hartwig, L.
  • Source: Soil Biology and Biochemistry
  • Volume: 34
  • Issue: 11
  • Year: 2002
  • Summary: Abstract: To explore the reason for reported high field fluxes of nitrous oxide (N2O) from temperate soils in winter and early spring, we investigated the temperature response of denitrifier N2O production and reduction in soil from three arable field sites along a temperature transect reaching from Finland over Sweden to Germany. Process rates were determined in anaerobic slurries with or without added NO3-, N2O and C2H2 at 0, 5, 10, 15, and 20C (and 30C in one experiment). The experiments were conducted immediately after the soils had become anaerobic, and after a long (48 h) anaerobic pre-incubation with excess of carbon and electron acceptors. All denitrifying enzymes were found to be active in the soil at onset of anaerobiosis. Significant levels of N2O production and reduction occurred at 0 8C, both at onset of anaerobiosis and after the 2 days anaerobic pre-incubation. Temperature response of N2O production and reduction could be fitted to an Arrhenius function in the range 5-20 °C, yielding apparent activation energies between 28 and 76 kJ mol -1. The estimated activation energy of the N2O reduction was found to be similar or lower than that for N2O production. High field N2O fluxes in winter and early spring could thus not be explained by the temperature sensitivity of the two processes. However, major deviations from the regular Arrhenius response were found for two soils at near freezing temperature. The rates measured at 0 °C were much lower than those predicted by the Arrhenius function based on data in the temperature range 5-20 °C. Low temperature may thus exert a particular challenge to denitrifying communities for some reason, and the effect was found to be most severe for the N2O reduction process. When such a breakdown affects N2O reductase to a greater extent than the N2O producing enzymes (NO3-, NO2-, and NO reductase), as was found in our soils, it will result in high N2O fluxes at low temperature. The temperature response of the estimated net N2O emission potential (based on measured N2O production and reduction rates) differed significantly between the three sites, indicating inherent differences between their microbial communities.
  • Authors:
    • Liang, B. C.
    • Zentner, R. P.
    • Sabourin, D.
    • Izaurralde, R. C.
    • Gameda, S.
    • McConkey, B. G.
    • Campbell, C. A.
  • Source: Agriculture Practices and Policies for Carbon Sequestration in Soil
  • Year: 2002
  • Authors:
    • Carter, M. R.
  • Source: Agronomy Journal
  • Volume: 94
  • Issue: 1
  • Year: 2002
  • Summary: Soil quality concepts are commonly used to evaluate sustainable land management in agroecosystems. The objectives of this review were to trace the importance of soil organic matter (SOM) in Canadian sustainable land management studies and illustrate the role of SOM and aggregation in sustaining soil functions. Canadian studies on soil quality were initiated in the early 1980s and showed that loss of SOM and soil aggregate stability were standard features of nonsustainable land use. Subsequent studies have evaluated SOM quality using the following logical sequence: soil purpose and function, processes, properties and indicators, and methodology. Limiting steps in this soil quality framework are the questions of critical limits and standardization for soil properties. At present, critical limits for SOM are selected using a commonly accepted reference value or based on empirically derived relations between SOM and a specific soil process or function (e.g., soil fertility, productivity, or erodibility). Organic matter fractions (e.g., macro-organic matter, light fraction, microbial biomass, and mineralizable C) describe the quality of SOM. These fractions have biological significance for several soil functions and processes and are sensitive indicators of changes in total SOM. Total SOM influences soil compactibility, friability, and soil water-holding capacity while aggregated SOM has major implications for the functioning of soil in regulating air and water infiltration, conserving nutrients, and influencing soil permeability and erodibility. Overall, organic matter inputs, the dynamics of the sand-sized macro-organic matter, and the soil aggregation process are important factors in maintaining and regulating organic matter functioning in soil.
  • Authors:
    • Ulmer, M. G.
    • Cihacek, L. J.
  • Source: Agriculture Practices and Policies for Carbon Sequestration in Soil
  • Year: 2002
  • Summary: from summary: "The significance of soils in sequestering greenhouse gases and reducing global warming may be greater due to C sequestration as inorganic C. Soil IC is a sink for atmospheric CO 2 , which may be more resistant to cropping and tillage effects on sequestered soil C and is likely to persist for decades and perhaps centuries after sequestration."
  • Authors:
    • Riedell, W. E.
    • Pikul, J. L.
    • Archer, D. W.
  • Source: Soil & Tillage Research
  • Volume: 67
  • Issue: 1
  • Year: 2002
  • Summary: Ridge tillage (RT) has been proposed as an economically viable conservation tillage alternative for row crop production; however the long-term economic viability of RT in the northern Corn Belt of the USA is largely unknown. Economic returns, risk and input use were compared for RT and conventional tillage (CT) in a corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) rotation with high, medium and low nitrogen treatments. The analysis was based on 10 years of experimental data from Brookings, SD on a Barnes clay loam (US soil taxonomy: fine-loamy, mixed, superactive, frigid Calcic Hapludoll; FAO classification: Chernozem). Economic returns were significantly higher at the highest nitrogen treatment levels. Highest average net returns to land and management were $ 78 per hectare for RT at the high nitrogen treatment level (RT-H) followed by $ 59 per hectare for CT at the high nitrogen treatment level (CT-H). Risk, measured as the standard deviation of net returns, was the lowest for CT at the medium nitrogen treatment level (CT-M) followed by RT-H and CT-H. However, net returns were substantially lower under CT-M at $ 32 per hectare. Average yields and average operating costs were not significantly different for RT-H and CT-H. Reduced equipment operating costs for CT-H were offset by increased herbicide costs for RT-H. Equipment ownership costs were significantly lower for RT-H than CT-H. There were no significant differences in fertilizer use for RT and CT. Pesticide use was significantly higher for RT-H than CT-H. Fuel use was 18-22% lower and labor use was 24-27% lower for RT-H than CT-H. Despite continued low adoption rates for RT in the northern Corn Belt, our analysis shows that RT is an economically viable alternative to CT.
  • Authors:
    • Azooz, R.
    • Soon, Y.
    • Arshad, M.
  • Source: Soil & Tillage Research
  • Volume: 65
  • Issue: 1
  • Year: 2002
  • Summary: In recent years, crop rotation and no-till farming have become common practices in Alberta, Canada, and are widely recommended to maintain and/or enhance soil quality for sustained crop production, and improve environmental quality. This study was undertaken to evaluate the effects of rape ( Brassica rapa [ B. napus var. oleifera]) and field pea ( Pisum sativum) as replacements for summer fallow on wheat ( Triticum aestivum) production, and to determine the role of tillage (no-till versus modified no-till) on crop production on an Albright silt loam (Mollic Cryoboralf) near Beaverlodge, Alta. Spring wheat was grown for 2 years of the 3-year cropping cycle. Crop sequences studied were: rape-wheat-wheat (RWW), field pea-wheat-wheat (PWW) and fallow-wheat-wheat (FWW). The control was continuous wheat, i.e. wheat-wheat-wheat or monoculture wheat (MW). In modified no-till, sweeps attached to the seed drill pushed crop residues aside from the centre 7.5 cm of the seed row. Wheat yield following field pea increased by an average (1997-99) of 10.5% compared to monoculture wheat. Our data showed no measurable effect of rape on succeeding wheat yields compared to monoculture wheat. Wheat yields following fallow were intermediate between the RWW and PWW cropping systems. Residue management through the modified no-till system resulted in a warmer seedbed during spring and improved wheat production in all crop rotations studied, especially the first succeeding wheat. Modified no-till also resulted in higher yields of rape but not pea. Our data indicate that in a 3-year rotation with wheat, the preferred break crop would be field pea for the cold semiarid region of Alberta.
  • Authors:
    • Lajeunesse, J.
    • Pageau, D.
    • Legere, A.
    • Simard, M.
    • Warwick, S.
  • Source: Weed Technology
  • Volume: 16
  • Issue: 2
  • Year: 2002
  • Summary: The presence of volunteer rape ( B. napus [ B. napus var. oleifera]) is becoming a significant agroecological concern, given the large-scale use of herbicide-tolerant varieties in some areas. Our goal was to estimate the frequency and persistence of volunteer rape in Quebec cropping systems by surveying fields that included a single rape crop since 1995 in Quebec, Canada. A survey was conducted in 131 fields in the main rape-growing areas of Quebec: in the Saguenay-Lac Saint-Jean region and the Quebec City-La Pocatiere area, Canada, during June-August 2000. Volunteer rape plants were counted in 0.25-m 2 quadrats every 10 m along a W pattern, and every 15 m along the margins of 88 fields. Volunteer rape plants were found in 90% of the fields surveyed and in a wide range of crops, including cereal, maize, and soyabean. Average densities of 4.9 and 3.9 plants/m 2 were found a year after rape production in fields and field margins, respectively. Volunteer rape densities decreased significantly over time. However, volunteer plants were still present at low densities 4 and 5 years after production. Dense stands of volunteer rape were found before postemergence herbicide application in no-till fields (9.84.1 plants/m 2), suggesting that, contrary to what was suggested in the literature, seeds could become dormant in no-till as well as in tilled systems. A small proportion of the volunteer rape plants observed in no-till fields near Quebec City and Ottawa included plants that had overwintered, either originating from autumn-germinated seedlings, harvested adult plants that had grown new leaves before the onset of winter, or spring regrowth from the base of unharvested adult plants from experimental plots. The presence and persistence of low densities of volunteer rape may not have been a cause of concern until now. However, producers should be made more aware of the potential short-term and long-term problems associated with potential gene flow between different herbicide-tolerant rape (HT rape) varieties and also between HT rape and related weed species.
  • Authors:
    • Ulrich, D.
    • Brandt, S. A.
    • Malhi, S. S.
    • Lemke, R.
    • Gill, K. S.
  • Source: Journal of Plant Nutrition
  • Volume: 25
  • Issue: 11
  • Year: 2002
  • Summary: Cropping systems can influence the accumulation and distribution of plant nutrients in the soil profile, which can affect their utilization efficiency by crops and pollution potential in the environment. A field experiment was conducted on a Dark Brown loam soil at Scott, Saskatchewan, Canada to assess the effects of input level, cropping diversity and crop phase on the accumulation and distribution of nitrate-nitrogen (N) and extractable phosphorus (P) in the soil profile at the end of 1995 to 2000 growing seasons. The 54 treatments were combinations of three input levels (organic-ORG, reduced-RED and high-HIGH), three cropping diversities (low diversity-LOW, diversified annual grains-DAG, and diversified annual and perennials-DAP), and six crop phases chosen from fallow (tillage-fallow or chemfallow), green manure [lentil-Lens culinaris Medicus or sweet clover-Melilotus officinalis (L.) Lam], spring wheat (Triticum aestivum L.), canola (Brassica napus L. and Brassica rapa L.), fall rye (Secale cereale L.), field pea (Pisum sativum L.), spring barley (Hordeum vulgare L.), flax (Linum usitatissimum L.), oats (Avena sativa L.), and bromegrass (Bromus inermis Leyss), alfalfa (Medicago sativa Leyss) mixture hay. Soil was sampled from the 0-15, 15-30, 30-60, and 60-90cm depths in each crop phase from 1995 to 2000, with additional depths 90-120, 120-150, 150-180, 180-210, and 210-240cm taken from the wheat phase in 2000. In general, there were greater amounts of nitrate-N with HIGH input compared to ORG or BID inputs, especially under LOW diversity. The nitrate-N in various soil depths suggested some downward movement of nitrate-N to the deeper soil depths when HIGH input was compared to ORG input. In LOW cropping diversity, green manure or fallow usually had more nitrate-N in soil than other crop phases. In DAG and DAP cropping diversities, nitrate-N varied with crops and on average it had maximum concentration after wheat or canola in DAG and after hay followed closely by wheat in DAP. The ORG input level had greater nitrate-N than RED or HIGH inputs in some instances, most likely due to relatively low extractable P in soil for optimum crop growth under ORG input. Extractable P in the 0-15 and 15-30 cm soil depths tended to be greater under HIGH or RED inputs compared to the ORG input level in many cases. In summary there was no consistent effect of cropping diversity on extractable P in soil under ORG input, but LOW diversity tended to show more extractable 13 compared to DAG and DAP diversities in some cases of RED and HIGH inputs. The green manure/fallow, HIGH input and LOW diversity treatments tended to result in higher nitrate-N and extractable P levels compared to the corresponding treatments, and the effects were more pronounced on nitrate-N than extractable P and in shallow compared to deeper soil layers.
  • Authors:
    • Nielsen, G.
    • Mortensen, D.
    • McGinn, S.
    • Coen, G.
    • Caprio, J.
    • Waltman, S.
    • Padbury, G.
    • Sinclair, R.
  • Source: Agronomy Journal
  • Volume: 94
  • Issue: 2
  • Year: 2002
  • Summary: The northern Great Plains have long been dominated by conventional tillage systems and cereal-based rotations including summer fallow. Over the last decade, however, the use of conservation tillage systems has markedly increased and, through improved moisture storage, has provided an opportunity for more diversified extended rotations including oilseed, pulse, and forage crops throughout the region. Considerable research is being carried out to assess the adaptability of these new crops and to develop appropriate management strategies. Typically, this type of agronomic research is carried out at plot-sized research sites, with the findings then being extrapolated to surrounding regions where growing conditions are thought to be reasonably similar. Because the environment itself largely dictates the success of a particular cropping system, extrapolation requires knowledge of the environmental conditions of the region and, in particular, the interaction of environmental components of soil and climate in relation to specific crop requirements. This paper describes 14 agroecoregions in the northern Great Plains and provides an initial framework for extrapolating agronomic information at broad regional scales. Because climate is the dominant crop production factor in the region, most of the agroecosystems represent broad climatic zones. Each agroecoregion is described in terms of its soil and landscape characteristics, with a particular focus being given to likely key environmental parameters related to the production of the new oilseed, pulse, and forage crops being introduced in the region.
  • Authors:
    • Krishnappan, B. G.
    • Stone, M.
  • Source: Water Research
  • Volume: 36
  • Issue: 14
  • Year: 2002
  • Summary: A field-scale no-till corn plot (120 m * 90 m) located on a tile drained silt loam soil near Kintore, Ontario was irrigated with 2.5 cm of water over a 3 h period to examine the effects of irrigation on tile sediment transport in a headwater stream. Flow characteristics and the composition, concentration and size distribution of suspended solids were measured at the tile outlet, an upstream reference site and three sites located downstream of the tile drain. Results show that tile sediments at the study site are fine-grained ( D50=5.0 m) and consist primarily of quartz, anorthite/albite, dolomite and calcite. Sediment concentrations in tile effluent increased from 8 to 57 mg L -1 after 1.5 h of irrigation and reached a maximum of 72 mg L -1. The sediment yield from the tile drain for the irrigation event was 4.6 kg ha -1. An unsteady, mobile boundary flow model (MOBED) was used to predict flow characteristics in the stream. According to the MOBED model, bed shear stress in the stream was approximately 6 N m -2. This value is significantly greater than the critical shear stress for complete suspension of 1 N m -2 for tile sediments as determined from laboratory experiments using a rotating circular flume. Grain size distributions of suspended solids in the stream were close to the dispersed size distribution because of the high shear stress in the receiving stream.