• 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:
    • Osborne, S. L.
    • Riedell, W. E.
    • Pikul, J. L. Jr.
  • Source: Recent Research Developments in Soil Science
  • Volume: 2
  • Year: 2007
  • Summary: Maize (Zea mays L.) grown in rotation with high residue crops generally has lower grain yield under no-till than under tilled soil management in the northern US maize belt. Hence, the research objectives were to further characterize soil physical properties, maize grain yield, and seed composition under tilled and no-till soil management following soybean ( Glycine max L.) or winter wheat ( Triticum aestivum L). The two year field study was conducted on a Barnes sandy clay loam soil (fine-loamy, mixed, superactive, frigid Calcic Hapludoll) in eastern South Dakota USA. Research plots were managed under no-till starting in 1996. Tillage treatments (fall chisel plow prior to winter wheat, fall chisel plow plus spring disk-harrow prior to maize and soybean, or no-till) were started in 2001. Tillage and previous crop treatments were arranged in a completely randomized block design with 4 replications. Soil temperatures (30 cm depth) in tilled plots after winter wheat were warmer than no-till plots in June and again in August of the 2004 growing season. In 2003, soil temperatures were very similar across tillage treatments. Soil bulk density (0 to 10 cm depth) and soil penetration resistance (0 to 7 cm depth) were much greater under no-till soil management than under tilled conditions when measured in mid-June (V6 leaf development stage). While tillage treatment affected maize seed oil concentration (4.0% in tilled, 4.3% in no-till), there were no significant previous crop or interaction effects on seed oil or protein concentration. In the warmer and drier year (2003), maize grain yield under tilled conditions was 8.2 Mg ha -1 compared with 8.7 Mg ha -1 under no-till. In the cooler and wetter year (2004), yields were 9.4 Mg ha -1 under tilled soil management and 7.4 Mg ha -1 under no-till. The no-till soil management treatment following winter wheat had 27% lower maize grain yield than the tilled treatments and the no-till following soybeans. We conclude that greater bulk density and penetration resistance levels under no-till soil management, along with cool soil conditions that typically occur in the spring in the northern US maize belt, reduced maize yield under no-till management in soils with moderately low to low internal drainage.
  • Authors:
    • Anderson, R. L.
  • Source: Weed Technology
  • Volume: 21
  • Issue: 2
  • Year: 2007
  • Summary: Weed management is evolving to include cultural tactics that reduce weed populations. This study near Brookings, SD, evaluated the effect of crop sequence and tillage on seedling emergence of common sunflower across years. In the third and fourth years of the study, seedling density was sevenfold greater after 2 yr of soyabean with tillage compared with a 2-yr sequence of canola and winter wheat with no-till. Apparently, canola and winter wheat enhanced the natural decline of common sunflower seed density in soil, leading to fewer seedlings in following years. In the first year of the study, tillage increased seedling emergence of common sunflower compared with no-till; seedlings rarely emerged in canola or winter wheat. Most seedlings of common sunflower emerged in May, with more than 90% of seedlings emerging between May 7 and June 4. Cool-season crops grown with no-till may affect weed seed survival in soil in the western Corn Belt.
  • Authors:
    • Anderson, R. L.
    • Beck, D. L.
  • Source: Weed Technology
  • Volume: 21
  • Issue: 1
  • Year: 2007
  • Summary: Producers in the Great Plains are exploring alternative crop rotations with the goal of reducing the use of fallow. In 1990, a study was established with no-till practices to compare 8 rotations comprising various combinations of winter wheat (W), spring wheat (SW), maize (C), chickpea (CP), dry pea (Pea), soyabean (SB), or fallow (F). After 12 years, we characterized weed communities by recording seedling emergence in each rotation. Downy brome ( Bromus tectorum), cheat ( Bromus secalinus), redroot pigweed ( Amaranthus retroflexus), and green foxtail ( Setaria viridis) were the most common weeds observed. Weed community density was highest for W-CP, being 13-fold greater than with Pea-W-C-SB. Downy brome and cheat were rarely observed in rotations where winter wheat was grown only once every 3 or 4 years; in contrast, density of the brome species was 75-fold greater in W-CP. Warm-season weeds were also affected by rotation design; density of redroot pigweed and green foxtail was 6-fold greater in W-C-CP compared with Pea-W-C-SB or W-F. One rotation design that was especially favourable for low weed density was arranging crops in a cycle of 4, with 2 cool-season crops followed by 2 warm-season crops.
  • Authors:
    • Merrill, S. D.
    • Krupinsky, J. M.
    • Tanaka, D. L.
    • Anderson, R. L.
  • Source: Journal of Soil and Water Conservation
  • Volume: 61
  • Issue: 1
  • Year: 2006
  • Summary: Soil coverage by residue protects soil and land resources from erosion, conserves soil water, and maintains soil quality. No-till and chemical weed control are management practices that increase soil coverage by residue. On the other hand, crop diversification in dryland agriculture in the northern Great Plains promotes the use of crops that produce significantly less soil coverage by residue than small cereal grains. Within a 10 x 10 crop sequence project under no-till in south-central North Dakota [409 mm (16.1 in) mean annual precipitation], all two-year crop sequence combinations of ten crops (barley, canola, crambe, dry bean, dry pea, flax, safflower, soybean, spring wheat, and sunflower) were evaluated at two adjacent sites. Soil coverage by residue was measured by transect and photographic techniques following spring wheat seeding. Soil coverage ranged from 98 to 89 percent following crop sequences that included spring wheat and barley. Soil coverage values were intermediate for spring wheat-alternative crop sequences, 97 to 62 percent. Crop sequences not including spring wheat with alternative crops for two years had values ranging from 86 to 35 percent. Soil coverage values after two consecutive years of sunflower or dry pea (two years of data) and two years of dry bean or safflower (single year of data) were in a lower range, 48 to 35 percent. Soil erosion hazards were evaluated with equations based on residue effects alone that were taken from the Revised Universal Soil Loss Equation (RUSLE) water erosion and Revised Wind Erosion Equation (RWEQ) wind erosion models: calculated soil loss ratio values (SLR = 1 with no residue protection) for 35 percent coverage following a sunflower-sunflower sequence were 0.29 for water erosion and 0.21 for wind erosion. Even with use of no-till, especially on more fragile soils, producers should consider planting a higher residue-producing crop (e.g., wheat, flax) the year before seeding lower residue-producing crops in order to assure adequate protection of soil and land resources.
  • Authors:
    • Miller, P. R.
    • Engel, R. E.
    • Holmes, J. A.
  • Source: Agronomy Journal
  • Volume: 98
  • Issue: 6
  • Year: 2006
  • Summary: Annual legumes permit intensified cropping in no-till systems in the drought-prone northern Great Plains. Our objectives were to compare cropping sequence effects of pea ( Pisum sativum L.) with fallow, mustard ( Sinapis alba L.), and wheat ( Triticum aestivum L.), and to measure the effects of pea harvest timing and shoot biomass presence on soil water use and N contribution, and yield and grain quality of subsequent wheat. Pea, mustard, wheat, and fallow preceded spring wheat at three sites in Montana. In the first year, two harvest timings (anthesis and maturity) were included and managed for presence or absence of crop shoot biomass. In the second year, a wheat test crop was grown at four N fertilizer rates. Regardless of management, pea used equal or less soil water, contributed equal or greater soil N, and had equal or greater positive impact on subsequent wheat growth than mustard or wheat. Compared with maturity, midseason harvest timing of pea increased soil N (30-39 kg NO 3-N ha -1) and soil water (19-39 mm) available in the spring to the subsequent wheat test crop at two of three sites. Under severe drought, midseason harvest of pea increased wheat yield 50% and critically increased grain density compared with the mature pea harvest. At the N-limited site, midseason harvest of pea increased wheat yield 14% and grain protein 9% compared with mature pea harvest. Pea shoot biomass presence did not affect soil water or N, or growth of a subsequent wheat crop.
  • Authors:
    • Paulitz, T. C.
  • Source: European Journal of Plant Pathology
  • Volume: 115
  • Issue: 3
  • Year: 2006
  • Summary: Direct-seeding or no-till is defined as planting directly into residue of the previous crop without tillage that mixes or stirs soil prior to planting. No-till reduces soil erosion, improves soil structure and organic matter, and reduces fuel inputs. No-till is widely used in cereal production in Australia, Canada, Argentina, and Brazil, but has not been widely adopted in Europe and the Pacific Northwest of the U.S. One of the limitations is that root diseases may increase with a reduction in tillage. This paper discusses the importance and management of take-all, Fusarium dryland foot rot, Rhizoctonia bare patch and root rot, and Pythium root rot in dryland cereal production systems, and how they are influenced by changes in tillage practices. To address this challenge, specifically with Rhizoctonia and Pythium, our research group has (1) developed classical and molecular techniques to detect and quantify Rhizoctonia and Pythium spp. from the soil to assess disease risk; (2) studied the disease dynamics of root disease during the transition from conventional to no-till; (3) developed greenhouse methods to screen germplasm for tolerance or resistance to Pythium and Rhizoctonia, and (4) using GPS and geostatistics, has examined the spatial distribution of R. solani and R. oryzae at a field scale up to 36 ha, across a number of crop rotations and years. By a combination of ecological, epidemiological, field, and laboratory studies, we hope to provide growers with a set of disease management tools to permit the economical and sustainable production of dryland cereals without degradation of the soil resource.
  • Authors:
    • Pitts, T.
    • Atwood, J. D.
    • Williams, J. R.
    • Potter, S. R.
    • Wang, X.
  • Source: Transactions of the ASABE
  • Volume: 49
  • Issue: 3
  • Year: 2006
  • Summary: Sensitivity analysis for mathematical simulation models is helpful in identifying influential parameters for model outputs. Representative sets of APEX (Agricultural Policy/Environmental eXtender) model data from across the U.S. were used for sensitivity analysis to identify influential parameters for APEX outputs of crop grain yields, runoff/water yield, water and wind erosion, nutrient loss, and soil carbon change for a national assessment project: the Conservation Effects Assessment Project (CEAP). The analysis was based on global sensitivity analysis techniques. A test case, randomly selected from the representative sets of APEX model data, was first analyzed using both the variance-based sensitivity analysis technique and the enhanced Morris method. The analysis confirmed the reliability of the enhanced Morris measure in screening subsets of influential and non-influential parameters. Therefore, the enhanced Morris method was used for the national assessment, where the cost of applying variance-based techniques would be excessive. Although sensitivities are dynamic in both temporal and spatial dimensions, the very influential parameters (ranking 1st and 2nd) appear very influential in most cases. Statistical analyses identified that the NRCS curve number index coefficient is very influential for runoff and water-related output variables, such as soil loss by water, N and P losses in runoff. The Hargreaves PET equation exponent, moisture fraction required for seed germination, RUSLE C factor coefficient, and the potential heat units are influential for more than two APEX outputs studied.
  • Authors:
    • Grace, P. R.
    • Colunga-Garcia, M.
    • Gage, S.
    • Safir, G.
    • Robertson, G. P.
  • Source: Ecosystems
  • Volume: 9
  • Issue: 5
  • Year: 2006
  • Summary: Soil organic carbon (SOC) represents a significant pool of carbon within the biosphere. Climatic shifts in temperature and precipitation have a major influence on the decomposition and amount of SOC stored within an ecosystem. We have linked net primary production algorithms, which include the impact of enhanced atmospheric CO2 on plant growth, to the Soil Organic Carbon Resources And Transformations in EcoSystems (SOCRATES) model to develop a SOC map for the North Central Region of the United States between the years 1850 and 2100 in response to agricultural activity and climate conditions generated by the CSIRO Mk2 Global Circulation Model (GCM) and based on the Intergovernmental Panel for Climate Change (IPCC) IS92a emission scenario. We estimate that the current day (1990) stocks of SOC in the top 10 cm of the North Central Region to be 4692 Mt, and 8090 Mt in the top 20 cm of soil. This is 19% lower than the pre-settlement steady state value predicted by the SOCRATES model. By the year 2100, with temperature and precipitation increasing across the North Central Region by an average of 3.9 C and 8.1 cm, respectively, SOCRATES predicts SOC stores of the North Central Region to decline by 11.5 and 2% (in relation to 1990 values) for conventional and conservation tillage scenarios, respectively.