• Authors:
    • Samu, F.
    • Sunderland, K.
  • Source: Entomologia Experimentalis Et Applicata
  • Volume: 95
  • Issue: 1
  • Year: 2000
  • Summary: A review of the literature showed that spider abundance was increased by diversification in 63% of studies. A comparison of diversification modes showed that spider abundance in the crop was increased in 33% of studies by `aggregated diversification' (e.g. intercropping and non-crop strips) and in 80% of studies by `interspersed diversification' (e.g., undersowing, partial weediness, mulching and reduced tillage). It is suggested that spiders tend to remain in diversified patches and that extending the diversification throughout the whole crop (as in interspersed diversification) offers the best prospects for improving pest control. There is little evidence that spiders walk in significant numbers into fields from uncultivated field edges, but diversification at the landscape level serves to foster large multi-species regional populations of spiders which are valuable as a source of aerial immigrants into newly planted crops. There are very few manipulative field studies where the impact of spiders on pests has been measured in diversified crops compared with undiversified controls. It is encouraging, however, that in those few studies an increased spider density resulted in improved pest control. Future work needs are identified.
  • Authors:
    • Blomert, B.
    • Gregorich, E. G.
    • Roloff, G.
    • Liang, B. -C.
    • Zentner, R. P.
    • Campbell, C. A.
  • Source: Canadian Journal of Soil Science
  • Volume: 80
  • Issue: 1
  • Year: 2000
  • Summary: Because crop management has a strong influence on soil C, we analyzed results of a 30-yr crop rotation experiment, initiated in 1967 on a medium textured Orthic Brown Chernozem at Swift Current, Saskatchewan, to determine the influence of cropping frequency, fertilizers and crop types on soil organic C (SOC) changes in the 0- to 15-cm depth. Soil organic C in the 0- to 15-cm and 15- to 30-cm depths were measured in 1976, 1981, 1984, 1990, 1993, and 1996, but results are only presented for the 0- to 15-cm depth since changes in the 15- to 30-cm depth were not significant. We developed an empirical equation to estimate SOC dynamics in the rotations. This equation uses two first order kinetic expressions, one to estimate crop residue decomposition and the other to estimate soil humus C mineralization. Crop residues (including roots) were estimated from straw yields, either measured or calculated from grain yields. The parameter values in our equation were obtained from the scientific literature or were based on various assumptions. Carbon lost by wind and water erosion was estimated using the EPIC model. We found that (i) SOC was increased most by annual cropping with application of adequate fertilizer N and P; (ii) that frequent fallowing resulted in lowest SOC except when fall-seeded crops, such as fall rye (Secale cereale L.), that reduce erosion were included in the rotation, and (iii) the fallow effects are exacerbated when low residue yielding flax (Linum usitatissimum L.) was included in the rotation. Some of the imprecision in SOC values we speculated to be related to variations in soil texture at the test site. In the first 10 yr of the experiment, SOC was low and constant for fallow-spring wheat (Triticum aestivum L.) (F-W) and F-W-W rotations because this land was managed in this manner for the previous 50 yr. However, in rotations that received N + P fertilizer and were cropped annually [continuous wheat (Cont W) and wheat-lentil (Lens culinaris L.)], or that included fall-seeded crops (e.g., F-Rye-W),SOC appeared to increase sharply in this period. In the drought period (1984–1988) SOC was generally constant, but large increases occurred in the wet period (1990 to 1996) in response to high residue inputs. The efficiency of conversion of residue C to SOC for the 30-yr experimental period was about 10–12% for F-W, F-W-W and Cont W (+P) systems, and it was about 17–18% for the well fertilized F-Rye-W, Cont W, and W-Lent systems. The average annual SOC gains (Mg ha–1 yr–1) between 1967 and 1996 were 0.11 for F-W (N + P), 0.09 for the mean of the three F-W-W rotations (N + P, + N, + P), 0.23 for F-Rye-W (N + P), 0.32 for Cont W (N + P), 0.12 for Cont W (+ P), and 0.28 for W-Lent (N + P). The corresponding mean estimated (by our equation) annual SOC gains for these rotations, were 0.06, 0.10, 0.16, 0.22, 0.14, and 0.22 Mg ha–1 yr–1, respectively. Because soil C measurements are usually so variable, we recommend that calculations such as ours may be employed to assist in the interpretation of measured C trends and to test if they seem reasonable.
  • Authors:
    • Alberta Agriculture and Rural Development
  • Year: 2000
  • Authors:
    • Miller, M.
  • Source: Canadian Journal of Plant Science
  • Volume: 80
  • Issue: 1
  • Year: 2000
  • Summary: The role of mycorrhizae in phosphorus nutrition of maize is related to the fact that the P concentration in maize shoots at the four- to five-leaf stage affects final grain yield. In the early 1980s greater early-season shoot-P concentration (mg/g) and P absorption (mg/plant) from a no-till compared to a conventional tillage system were observed in Guelph, Ontario, Canada. Further studies established that the greater P absorption is due to a more effective arbuscular mycorrhizal (AM) symbiosis when the soil is not disturbed. The greater P absorption is largely a result of the undisrupted mycelium present in an undisturbed soil, rather than to increased colonization. This mycelium retains viability through extended periods in frozen soil. In the spring this mycelia network is able to acquire P from the soil and deliver it to the plant immediately upon becoming connected to a newly developing root system. Increased P absorption has not resulted in increased grain yield in field trials. Some additional factor limits yield with no-till maize preventing the advantage of early P absorption from being realized as yield. When maize follows a non-mycorrhizal crop such as rape, mycorrhizal colonization is delayed, reducing early-season P absorption. Yield reductions may occur.
  • Authors:
    • Knezevic, S. Z.
    • Leeson, J. Y.
    • Thomas, A. G.
    • Acker, R. C. van
    • Frick, B. L.
  • Source: Canadian Journal of Plant Science
  • Volume: 80
  • Issue: 4
  • Year: 2000
  • Summary: In 1997, a weed survey was conducted during July and August in fields of wheat, barley, oat, canola [rape] and flax in Manitoba, Canada. Field selection was based on a stratified-random sampling methodology using ecodistricts as strata. Species in the Poaceae family were most commonly observed in the survey, followed by species in the Polygonaceae, Asteraceae and Brassicaceae families. The six most abundant weed species were green foxtail ( Setaria viridis), wild oats ( Avena fatua), wild buckwheat ( Polygonum convolvulus) [ Fallopia convolvulus], Canada thistle ( Cirsium arvense), red-root pigweed ( Amaranthus retroflexus) and wild mustard ( Sinapis arvensis). The survey highlighted significant differences between ecoregions and between crops in residual weed infestations. The weed community in the Boreal Transition ecoregion was dominated by seven species, whereas fields in the Aspen Parkland and Lake Manitoba Plain ecoregions were dominated by two species and the Interlake Plain ecoregion was dominated by only one species. Although significant differences were found between the weed communities in crops, they were not as great as differences between ecoregions. The Manitoba residual weed community in 1997 was very similar to that reported for 1978-81 and 1986, suggesting that the same species should remain a focus for weed management.
  • Authors:
    • Black, A. L.
    • Krupinsky, J. M.
    • Merrill, S. D.
    • Halvorson, A. D.
  • Source: Agronomy Journal
  • Volume: 91
  • Issue: 4
  • Year: 1999
  • Summary: Winter wheat (Triticum aestivum L.) can add diversity to dryland crop rotations in the northern Great plains, but it is susceptible to winterkill in low surface residue environments. A 12-year study was conducted to determine the response of two winter wheat cultivars, Roughrider and Norstar; to tillage system (conventional-till, CT; minimum-till, MT: and no-till, NT) and N fertilizer rate (34, 67, and 101 kg N ha(-1)) in a dryland spring wheat-winter wheat-sunflower (Helianthus annuus L,) rotation. Grain yields were greater with MT (1968 kg ha(-1)) and NT (2022 kg ha(-1)) than with CT (1801 kg ha(-1)), but tillage system effects on grain yield varied among years, Increasing N rate from 34 kg N ha(-1) to 67 kg N ha(-1) increased grain production from 1844 to 1953 kg ha(-1), but yield response to N rate varied among years., The greatest overall grain yield (2111 kg ha(-1)) if as obtained with NT and application of 101 kg N ha(-1). Grain yields were lowest during gears when plant-available Hater (PAW) was 400 an PAW, leaf spot disease incidence was greatest, particularly at the lowest N rate with NT. Application of adequate N reduced the disease incidence in all tillage treatments. Cultivar differences Here significant 3 out of 12 years, but not consistent. Winterkill was a factor for both cultivars in only 1 year in the CT and MT plots. Winter wheat performed Hell as a rotational crop in this cropping system when using,tfT and NT systems and adequate N fertility, Our long-term results indicate that producers in the northern Great Plains ran use winter wheat successfully in annual cropping systems that do not include a fallow period, particularly if NT is used with adequate N fertilization.
  • Authors:
    • Merrill, S. D.
    • Tanaka, D. L.
    • Black, A. L.
    • Halvorson, A. D.
    • Krupinsky, J. M.
  • Source: Agronomy Journal
  • Volume: 91
  • Issue: 4
  • Year: 1999
  • Summary: Sunflower (Helianthus annuus L.) is a warm-season, intermediate water-use crop that can add diversity to dryland crop rotations, Reduced tillage systems may Enhance sunflower yield in intensive cropping systems. A 12-year study was conducted to determine how sunflower cultivars of early and medium maturity respond to tillage system (conventional-till, CT; minimum-till, MT; no-till, NT) and N fertilization (34, 67, and 101 kg N ha(-1)) within a dryland spring wheat (Triticum aestivum L.)-winter wheat-sunflower rotation. Averaged across N rates, cultivars, and years, sunflower seed yields were greater with MT (1550 kg ha(-1)) than with NT (1460 kg ha(-1)) and CT (1450 kg ha(-1)). Increasing N rate above 34 kg N ha-L generally increased gain yield, but varied from year to year. The tillage X N interaction showed that the highest seed yields were obtained with NT (1638 kg ha(-1)) and MT (1614 kg ha(-1)) at 101 kg N ha(-1). Total plant-available water (TPAW) of 500 mm did not result in increased sunflower yields over those with 350 to 500 mm TPAW. Yield differences between cultivar maturity classes varied from year to gear and with tillage and N level. At the lowest N rate, weeds were more problematic in NT than in CT and MT plots. More N fertilizer may be needed with NT to optimize sunflower yields than with CT and MT, because of less residual soil NO3-N with NT. Results indicate that producers in the northern Great Plains can use sunflower successfully in annual a cropping systems, particularly if MT and NT are used with adequate N fertilization.
  • Authors:
    • Azooz, R. H.
    • Franzluebbers, A. J.
    • Arshad, M. A.
  • Source: Soil & Tillage Research
  • Volume: 53
  • Issue: 1
  • Year: 1999
  • Summary: Improvement in soil quality to maintain high production and reduce negative environmental impacts is necessary for alternative crop production strategies to become socially acceptable and viable in the long-term. No-tillage (NT) management of the predominantly small grain region of western Canada has the potential to curb soil erosion and increase profitability. An understanding of the direct effects of NT on soil properties is necessary to evaluate its potential for sustained long-term productivity. We have compiled data collected from two sites in northern British Columbia to ascertain the long-term effects of conventional tillage (CT) and NT on soil components thought to be important in surface soil structural improvement. Soil water retention was greater under NT compared with CT without dramatically altering bulk density due to redistribution of pore size classes into more small pores and less large pores. Soil organic C was greater under NT than under CT nearest the soil surface. Water-stable aggregation improved under NT compared with CT, perhaps because more soil organic C was sequestered within macroaggregates under NT compared with CT that helped to stabilize these aggregates. Steady-state water infiltration was greater under NT than under CT as a result of soil structural improvements associated with surface residue accumulation and lack of soil disturbance. Barley (Hordeum vulgave L.) yield tended to be greater under NT than under CT in years of low rainfall as a result of improvements in soil water retention and transmission that may have provided a better environment for root development. Our data indicate that NT is a viable management strategy to improve soil quality in the cold, semiarid region of western Canada. This strategy could lead to high production, minimal negative environmental impacts, and a socially-acceptable farming system.
  • Authors:
    • Dickey, P.
    • Ward, M.
    • Graham, S.
    • Bryden, A.
    • McGill, W. B.
    • Izaurralde, R. C.
  • Source: Management of Carbon Sequestration in Soil
  • Year: 1998
  • Authors:
    • Zentner, R. P.
    • McGill, W. B.
    • Juma, N.
    • Ellert, B. H.
    • Izaurralde, R. C.
    • Campbell, C. A.
    • Janzen, H. H.
  • Source: Soil & Tillage Research
  • Volume: 47
  • Issue: 3
  • Year: 1998
  • Summary: The Canadian prairie, which accounts for about 80% of Canada's farmland, has large reserves of soil organic carbon (SOC). Changes in the size of the SOC pool have implications for soil productivity and for atmospheric concentrations of CO2, an important 'greenhouse gas'. We reviewed recent findings from long-term research sites to determine the impact of cropping practices on SOC reserves in the region. From this overview, we suggest that: (1) the loss of SOC upon conversion of soils to arable agriculture has abated; (2) significant gains in SOC (typically about 3 Mg C ha-1 or less within a decade) can be achieved in some soils by adoption of improved practices, like intensification of cropping systems, reduction in tillage intensity, improved crop nutrition, organic amendments, and reversion to perennial vegetation; (3) changes in SOC occur predominantly in 'young' or labile fractions; (4) the change in SOC, either gain or loss, is of finite duration and magnitude; (5) estimates of SOC change from individual studies are subject to limitations and are best viewed as part of a multi-site network; and (6) the energy inputs into agroecosystems need to be included in the calculation of the net C balance. The long-term sites indicate that Canadian prairie soils can be a net sink for CO2, though perhaps only in the short term. These sites need to be maintained to measure the effects of continued agronomic evolution and predicted global changes.