• Authors:
    • Hubbard, K. G.
    • Mahmood, R.
  • Source: Journal of Hydrology
  • Volume: 280
  • Issue: 1/4
  • Year: 2003
  • Summary: Soil moisture (SM) plays an important role in land surface and atmospheric interactions. It modifies energy balance at the surface and the rate of water cycling between the land and atmosphere. In this paper we provide a sensitivity assessment of SM and ET for heterogeneous soil physical properties and for three land uses including irrigated maize, rainfed maize, and grass at a climatological time-scale by using a water balance model. Not surprisingly, the study finds increased soil water content in the root zone throughout the year under irrigated farming. Soil water depletes to its lowest level under rainfed maize cultivation. We find a 'land use' effect as high as 36 percent of annual total evapotranspiration, under irrigated maize compared to rainfed maize and grass, respectively. Sensitivity analyses consisting of comparative simulations using the model show that soil characteristics, like water holding capacity, influence SM in the root zone and affect seasonal total ET estimates at the climatological time-scale. This 'soils' effect is smaller than the 'land use' effect associated with irrigation but, it is a source of consistent bias for both SM and ET estimates. The 'climate' effect basically masks the 'soils' effect under wet conditions. These results lead us to conclude that appropriate representation of land use, soils, and climate are necessary to accurately represent the water and energy balance in real landscapes.
  • Authors:
    • Norman, J. M.
    • Morgan, C. L. S.
    • Lowery, B.
  • Source: Soil Science Society of America Journal
  • Volume: 67
  • Issue: 2
  • Year: 2003
  • Summary: The variability of crop yield in dryland production is primarily affected by the spatial distribution of plant-available water even for seemingly uniform fields. The most productive midwestern soils, which are loess caps over glacial till or outwash, can have a wide range of water-holding capacities in individual fields because of landscape processes and management. An inverse yield model was created as a robust method to quantify the spatial and temporal role of plant-available water on large agricultural fields to improve management options in precision agriculture. Plant-available water maps for a field were estimated from yield maps using inverse water-budget modeling based on measurements of solar radiation, temperature, precipitation, and vapor pressure deficit. The model presented in this paper was applied to 5 yr of corn ( Zea mays L.) yield-monitor data from a field in Waunakee, WI, having three soil mapping units, Plano silt loam (fine-silty, mixed, mesic Typic Argiudoll), St. Charles silt loam (fine-silty, mixed, mesic Typic Hapludalf), and Griswold loam (Fine-loamy, mixed, mesic Typic Argiudoll). The comparison of measured and inverse-modeled plant-available water suggests that the simple inverse yield model produces reasonable results in drier years with uncertainties of about 28 mm of plant-available water. The model helped to quantify the role of plant-available water in determining crop yield. Because of limited input requirements, the model shows promise as a practical tool for using precision farming to improve management decisions, and as a tool to obtain input for landscape-based models.
  • Authors:
    • Mir, Z.
    • Acharya, S. N.
    • Moyer, J. R.
    • Doram, R. C.
  • Source: Canadian Journal of Plant Science
  • Volume: 83
  • Issue: 1
  • Year: 2003
  • Summary: Fenugreek (Trigonella foenum-graecom L.) is an annual legume that has potential as a forage crop on the Canadian Prairies. Experiments were established to determine the tolerance of fenugreek to several herbicides and their efficacy on various weeds. Potentially, fenugreek could be grown in conservation tillage systems in rotation with other annual crops. Therefore, additional multi-factor experiments were conducted to determine the effect of herbicides, seeding method, and 11 previous crops on fenugreek yield. Without herbicide application, weeds contributed 37 to 86% to total dry matter production. When imazamox/imazethapyr, or-combinations of imazamoz/imazethapyr or imazethapyr with ethalfluralin was applied, weed contents were about 5% of the total dry matter and the herbicides did not reduce fenugreek yield compared to the hand-weeded check. Total forage samples with a low weed content had lower fibre content and higher protein and digestible dry matter content than forages with a high weed content. When imazamox/imazethapyr was used for weed control, fenugreek yields and weed biomass were similar after direct seeding and after cultivation plus seeding. In addition, the effect of previous crop and the previous crop by seeding method interaction was not significant for fenugreek yield and weed biomass. Therefore, irrigated fenugreek can be successfully grown in conservation tillage systems in rotation with several crops provided an effective herbicide is used for weed control.
  • Authors:
    • Galatowitsch, S. M.
    • Mulhouse, J. M.
  • Source: Plant Ecology
  • Volume: 169
  • Issue: 1
  • Year: 2003
  • Summary: In the mid-1980's, thousands of wetlands in the mid-continental Unites States were restored by interrupting drainage lines; revegetation of these systems, often cropped for decades and positioned in a predominantly agricultural landscape, relied solely on natural recolonization. A study of 64 of these wetlands determined that by 1991, three years after initial reflooding, aquatic species had efficiently recolonized whereas sedge meadow and wet prairie species had not. In 2000, 41 of these restorations that had not been significantly altered or returned to cultivation were revisited and their floras characterized by cover within distinct zones. While species richness increased on every site, the rate of accumulation varied widely. Furthermore, species that had colonized since 1991, including a variety of native wet prairie and sedge meadow species, were detected only at very low abundance. In contrast, Phalaris arundinacea L., an invasive perennial, was now present on every site, often at covers approaching 75-100% in the zones in which it occurred. Other invasive perennials, including Cirsium arvense (L.) Scop. and Typha angustifolia L./glauca Godr., had expanded significantly on many sites. The overall dominance of invasive perennials has resulted in basins that are becoming more similar over time. However, present variations in species richness and composition can be attributed to flooding frequency, and, potentially, basin size and isolation from nearby natural wetlands, as shown by TWINSPAN and graphical analysis. Basins that have not been flooded at midsummer for at least seven of 12 years are among the most depauperate in the study. Yet even frequently flooded basins lack diversity if they are small (
  • Authors:
    • Soon, Y. K.
    • O'Donovan, J. T.
    • Drabble, J. C.
    • Darwent, A. L.
    • Milis, P. F.
    • Clayton, G. W.
    • Rice, W. A.
  • Source: Canadian Journal of Plant Science
  • Volume: 83
  • Issue: 1
  • Year: 2003
  • Summary: A study was conducted on the Agriculture and Agri-Food Canada Research Farm, Beaverlodge, Alberta, to compare nine cropping systems in relation to productivity and wild oat (Avena fatua L.) control. The nine cropping systems consisted of three crop rotations and three levels of banded N fertilizer. Each cropping system had its own regime of tillage and weed control. One of the rotations consisted of mechanical fallow, along with canola (Brassica rapa L.), barley (Hordeum vulgare L.) and wheat (Trificum aestivum L.), while the other two rotations consisted of the same annual crops, but with either flax (Linum usitatissimum L.) or red clover (Trifolium pratense L.) plowdown with partial fallow substituted for mechanical fallow. The three rates of banded N fertilizer were 0, 75 and 150% of recommended, based on soil tests and provincial recommendations. From 1991 to 1994, cropping systems with mechanical fallow and fall tillage after annual crops produced 24% higher total seed yields than cropping systems with no fall tillage after annual crops and either continuous annual crops or red clover plowdown. Increasing the rate of banded N fertilizer from 0 to 75% of recommended increased total crop seed yields but a further increase from 75 to 150% had no significant effect. Although cropping systems with mechanical fallow had an advantage over other cropping systems, the effect of crop sequencing and yearly weather conditions on total crop seed yields was greater than the effect of cropping systems. Wild oat populations varied greatly with year, but the ease of management was greater in cropping systems with the mechanical fallow than in other cropping systems. Wild oat density increased when diclofop or difenzoquat performed inadequately or when poor red clover establishment allowed populations to increase. Reductions in wild oat populations appeared to be largely due to the consistent effectiveness of sethoxydim.
  • Authors:
    • Jones, R. H.
    • Leonard, B. R.
    • Gore, J.
  • Source: Environmental Entomology
  • Volume: 32
  • Issue: 1
  • Year: 2003
  • Summary: Field and laboratory studies evaluated the influence of selected crop hosts on Helicoverpa zea population dynamics in relation to genetically engineered Bt (Bollgard) and non-Bt cottons. Host specific H. zea colonies were initiated with a colony originally collected from sweetcorn. The colony was allowed to complete one generation on meridic diet then split into cohorts and allowed to complete one generation on field maize, grain sorghum, soyabean, cotton, or meridic diet in individual 29.5 ml plastic cups. During the first part of the study, larval developmental times, pupal weights, and survival were measured. H. zea survival was higher on meridic diet and grain sorghum than on soyabean and cotton. The development of H. zea larvae was faster on field maize than the other larval diets. Also, H. zea required a longer period of time to complete development on cotton than on the other hosts. Pupal weights were higher on meridic diet than the plant hosts. Pupal weights of H. zea that completed larval stadia on cotton were lower than on the other larval diets. Neonates (F 1) from each of the host specific colonies (200 per colony) were exposed to Bt and non-Bt cottons. Mortality of second generation H. zea on non-Bt and Bt cottons was measured at 96 h. H. zea larvae from the cotton colony had higher mortality on non-Bt cotton than the other host specific colonies except the grain sorghum colony. On Bt cotton, larvae from the maize colony had a higher level of mortality than larvae from the soyabean and grain sorghum colonies. These data provide valuable information for evaluating the contribution of cultivated hosts as additional, alternative refugia in Bt-cotton resistance management plans.
  • Authors:
    • Blackshaw, R. E.
    • Clayton, G. W.
    • Harker, K. N.
    • O'Donovan, J. T.
    • Stevenson, F. C.
  • Source: Canadian Journal of Plant Science
  • Volume: 83
  • Issue: 2
  • Year: 2003
  • Summary: Implementing a favourable agronomic practice often enhances canola production. Combining several optimal practices may further increase production, and, given greater crop health and competitiveness, could also improve weed control. A field experiment was conducted at Lacombe and Lethbridge, Alberta, from 1998 to 2000, to determine the optimal combination of glufosinate-tolerant cultivar (hybrid In Vigor 2153 or open-pollinated Exceed), crop seeding rate (100, 150, or 200 seeds m(-2)) and time of weed removal (two-, four-, or six-leaf stage of canola) for canola yield and weed suppression. At equal targeted seeding rates, the hybrid cultivar had greater seedling density (8 plants m(-2) higher) and seed yield (22% higher) when compared with the open-pollinated cultivar. Combining the better cultivar with the highest seeding rate, and the earliest time of weed removal led to a 41% yield increase compared with the combination of the weaker cultivar, the lowest seeding rate and the latest time of weed removal. The same optimal factor levels also favoured higher levels of weed control and lower weed biomass variability. Managing these factors at optimal levels may help increase net returns, reduce herbicide dependence and favour the adoption of more integrated weed management systems.
  • Authors:
    • Bundy, L. G.
    • Andraski, T. W.
    • Kilian, K. C.
  • Source: Journal of Environmental Quality
  • Volume: 32
  • Issue: 5
  • Year: 2003
  • Summary: Manure additions to cropland can reduce total P losses in runoff on well-drained soils due to increased infiltration and reduced soil erosion. Surface residue management in subsequent years may influence the long-term risk of P losses as the manure-supplied organic matter decomposes. The effects of manure history and long-term (8-yr) tillage [chisel plow (CP) and no-till (NT)] on P levels in runoff in continuous corn (Zea mays L.) were investigated on well-drained silt loam soils of southern and southwestern Wisconsin. Soil P levels (0-15 cm) increased with the frequency of manure applications and P stratification was greater near the surface (0-5 cm) in NT than CP. In CP, soil test P level was linearly related to dissolved P (24-105 g ha(-1)) and bioavailable P (64-272 g ha(-1)) loads in runoff, but not total P (653-1893 g ha(-1)). In NT, P loads were reduced by an average of 57% for dissolved P, 70% for bioavailable P, and 91% for total P compared with CP. This reduction was due to lower sediment concentrations and/or lower runoff volumes in NT. There was no relationship between soil test P levels and runoff P concentrations or loads in NT. Long-term manure P applications in excess of P removal by corn in CP systems ultimately increased the potential for greater dissolved and bioavailable P losses in runoff by increasing soil P levels. Maintaining high surface residue cover such as those found in long-term NT corn production systems can mitigate this risk in addition to reducing sediment and particulate P losses.
  • Authors:
    • Kirkland, K. J.
    • Beckie, H. J.
  • Source: Weed Technology
  • Volume: 17
  • Issue: 1
  • Year: 2003
  • Summary: Model simulations predict that lowering herbicide efficacy by reducing the application rate would slow the rate of enrichment of herbicide-resistant individuals in a weed population, but the resulting increase in density of susceptible plants would reduce crop yield and increase the weed seed bank. A study was conducted at three sites in Saskatchewan, Canada, from 1997 to 2000 to examine the implication of reduced rates of acetyl-CoA carboxylase (ACCase) inhibitors in a diverse 4-yr crop rotation, in conjunction with variable crop seeding rates, on the enrichment of resistant wild oat in a mixed (resistant and susceptible) population. Main-plot treatments were crop (barley, canola, field pea, and spring wheat), subplot treatments were crop seeding rate (recommended and high), and sub-subplot treatments were ACCase inhibitor rate (0, 0.33, 0.67, and 1.0 times the recommended rate). Herbicide rate frequently interacted with seeding rate in affecting wild oat seedling density, seed return, the viable fraction of the weed seed bank, and crop seed yield. As simulation models predict, reduced herbicide efficacy decreased the proportion of resistant individuals in the population. The high crop seeding rate compensated for a one-third reduction in herbicide rate by limiting total wild oat seed return and by reducing the number of resistant seedlings recruited from the seed bank. The level of resistance in the seed bank can be reduced without increasing the total (resistant plus susceptible) seed bank population by manipulating agronomic practices to increase crop competitiveness against wild oat when ACCase inhibitor rates are reduced to a maximum of two-thirds of that recommended.
  • Authors:
    • Fielding, D. J.
    • Begna, S. H.
  • Source: Journal of Economic Entomology
  • Volume: 96
  • Issue: 4
  • Year: 2003
  • Summary: We characterized the type and extent of grasshopper injury to above- and below-ground plant parts for four crops, i.e. barley ( Hordeum vulgare), oats ( Avena sativa), wheat ( Triticum aestivum), and canola [turnip rape] ( Brassica campestris [ B. campestris var. oleifera]), commonly grown, or with potential to grow, in central Alaska, USA. Cages were placed on 48 pots containing plants in second to third leaf stages and stocked with 0, 2, 4, and 6 first-instar Melanoplus sanguinipes pot -1. Plants were harvested 22 days after planting. Stem growth of barley and oats was not affected except at the highest grasshopper treatment. In rape, stem biomass was reduced at the medium and high grasshopper treatments, when most of the leaves had been consumed. The highest grasshopper treatment reduced leaf area in barley and oats by ~55%, and caused a significant reduction in dry weight of leaves, stems, and roots (41-72%). Wheat and canola plants were smaller than barley and oats across all treatments and, at the highest grasshopper density, above-ground portions of wheat and canola were completely destroyed. Length and surface area of roots of barley and oats were reduced by 20-28% again at the highest grasshopper density, whereas the reduction for wheat and canola ranged from 50 to 90%. There was little or no difference among all grasshopper densities for C:N ratio in leaf and stem tissues of all crops. The results suggest that wheat and canola are more susceptible than barley and oats and that densities ≥2 pot -1 (~≥50 m -2) of even very small grasshoppers could cause significant damage in small-grain and oilseed crop production.