79 research outputs found

    Weed economic thresholds : Useful agronomic tool or pipe dream?

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    L'intĂ©rĂȘt pour des approches de lutte contre les mauvaises herbes plus ration nelles et objectives s'est considĂ©rablement accru au Canada et ailleurs. Les questions de coĂ»t/bĂ©nĂ©fices, les prĂ©occupations environnementales et le dĂ©veloppement de la rĂ©sistance aux herbicides ont semĂ© le doute sur la pertinence et la possibilitĂ© de poursuivre l'utilisation prĂ©ventive des herbicides. Le concept de seuil d'intervention Ă©conomique pour les mauvaises herbes et le concept plus large de lutte intĂ©grĂ©e prĂ©sentent un potentiel important comme outils agronomiques pratiques dans les systĂšmes de production canadiens. Un grand nombre d'expĂ©riences ont Ă©tĂ© menĂ©es afin de dĂ©terminer l'impact des mauvaises herbes sur le rendement des cultures, mais les modĂšles dĂ©veloppĂ©s Ă  partir de ces Ă©tudes ont Ă©tĂ© peu mis en pratique. Les contraintes Ă  la mise en pratique de ces concepts comprennent l'absence de protocoles d'Ă©chantillonnage rĂ©alistes afin de dĂ©terminer l'impact des mauvaises herbes sur les cultures sur de vastes Ă©tendues, ainsi qu'un manque de renseignements sur les implications Ă  long terme de la production de graines par les mauvaises herbes non contrĂŽlĂ©es. Les malherbologistes qui mĂšnent des expĂ©riences sur l'interfĂ©rence causĂ©e par les mauvaises herbes devraient mieux dĂ©finir leurs objectifs et devraient fournir des directives sur la façon dont leurs rĂ©sultats peuvent ĂȘtre utilisĂ©s Ă  la ferme. L'accent devrait ĂȘtre placĂ© sur l'effet des cultures sur les mauvaises herbes plutĂŽt que sur l'effet des mauvaises herbes sur les cultures. Une meilleure coordination des activitĂ©s de recherche des malherbologistes s'impose. La mise en place de protocoles standards pour les Ă©tudes Ă  long terme entre les sites et les annĂ©es augmenterait la pertinence et la prĂ©cision des modĂšles d'interfĂ©rence, et pourrait conduire au dĂ©veloppement de systĂšmes d'aide Ă  la dĂ©cision conviviaux et adaptĂ©s spĂ©cifiquement Ă  la prise de dĂ©cisions rationnelles de lutte contre les mauvaises herbes dans les systĂšmes canadiens de production des cultures. Le dĂ©veloppement de tels systĂšmes sera essentiel Ă  la mise en place de seuils d'intervention et de mĂ©thodes de lutte intĂ©grĂ©e contre les mauvaises herbes.Interest in more rational and objective approaches to weed management has increased considerably in Canada and elsewhere. Cost/benefit issues, environmental concerns, and the development of weed resistance to herbicides have cast doubt on the rationality and sustainability of prophylactic herbicide use. The concept of an economic threshold for weeds and the broader concept of integrated weed management have considerable potential as practical agronomic tools in Canadian crop production Systems. A large number of experiments have been conducted to determine the impact of weeds on crop yield, but the models developed from these studies have been put to little practical use. Constraints to the practical implementation of these concepts include a lack of realistic sampling procedures to assess the impact of weeds on crops over large areas, and a lack of information on the long-term implications of seed production by uncontrolled weeds. Weed ecologists conducting weed interference experiments should define their objectives better, and should provide guidelines on how their findings can be used at the farm level. Emphasis should be placed on the effects of the crop on the weed rather than the weed on the crop. There is also a need for greater coordination of research activities among weed ecologists. The establishment of standard protocols for long-term studies across locations and years would enhance the relevance and precision of weed interference models, and lead to the development of user- friendly decision support Systems specifically adapted to aiding rational weed management decisions in Canadian crop production Systems. The development of such Systems will be essential to the implementation of weed thresholds and integrated weed management

    \u3cem\u3eBrassica Carinata\u3c/em\u3e Growth and Yield Response to Nitrogen and Sulfur Fertilizers and Impacts on Selected Soil Parameters and GHG Fluxes

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    Carinata (Brassica carinata A. Braun), a non-food oilseed crop and an alternative bio-jet fuel feedstock, has received attention for its potential as a low-input option for production in the semi-arid regions of the Northern Great Plains of USA. The crop has a lower N fertilizer requirement as compared to the other oilseeds, suggesting less negative impact on soils and GHGs emissions. Carinata is a new crop to South Dakota (SD), thus, the best management practices have yet to be developed. In addition, no sufficient research to address the impact of growing carinata on soils and GHG emissions has been reported. The objectives of the study were to: (i) evaluate the response of seed yield and agronomic traits for carinata to N and S fertilizer rates, and (ii) evaluate the impact of growing carinata with different rates of N and S fertilizers on select soil properties and GHG emissions. Field experiments were conducted in 2017 and 2018 to assess the response of carinata to four N rates (56, 84, 112 and 140 kg N ha-1) and three S rates (0, 22 and 45 kg S ha-1) and) at Brookings, SD under conventional tillage. Increasing N fertilizer rate significantly increased plant height, branching, lodging severity, number of pods plant-1 but significantly decreased seed oil concentration. Increasing S fertilizer rate significantly increased plant height, branching, agronomic traits, seed yield, and seed oil concentration. This study showed that the economically optimal N rate was 85 kg N ha-1 and the economically optimal S rate was 36 kg S ha-1. Application of N fertilizer had minimal impact on soil parameters; N fertilizer increased soil EC, soil organic carbon (SOC), stable carbon, labile N, soil K, and soil P. Sulfur fertilizer decreased soil EC, SOC, labile N, and soil inorganic N content but increased extractable S content. Results from GHG emissions showed that, in addition to soil temperature and moisture conditions, N fertilizer increased CO2 and N2O emissions, whereas, S fertilizer application did not affect emissions. Methane fluxes fluctuated due to the impact of soil temperature and moisture. Findings from this study suggested that carinata has low nutrient requirements compared to the traditional crops grown in SD, and optimum N and S requirements for this crop were developed. This study also suggested that, in general, carinata has minimal impacts on soils and GHG emissions, however, a long-term monitoring of soils and GHG fluxes under different rotations, soils and environmental conditions can be beneficial in understanding the impacts associated with carinata production

    Chronic tropospheric ozone exposure reduces seed yield and quality in spring and winter oilseed rape

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    Oilseed rape (Brassica napus L.) is cultivated worldwide, producing 11.5% of global oilseeds at an economic value of 38 billion USD in 2020. It is sensitive to phytotoxic damage from exposure to tropospheric ozone (O3), a major air pollutant, which disrupts plant physiological processes and thus decreases biomass accumulation. As background ozone concentrations continue to increase globally, we investigated the impact of ozone exposure on seed and oil yield of a shorter-lived spring (cv. Click) and a longer-lived winter (cv. Phoenix) oilseed rape cultivar to ozone levels (treatments with peaks of 30, 55, 80, 110 ppbv) representative of typical European conditions where these cultivars are common. Thousand Seed Weight (TSW), an important measure of final yield, decreased more in Phoenix (40%) than Click (20%) with increasing ozone exposure. Click produced more racemes and many small seeds while Phoenix produced fewer racemes and larger seeds. However, seed quality declined more substantially in Click than Phoenix. The oil content in Click's seed significantly decreased with increased ozone exposure, while less desirable components (moisture, chlorophyll, ash) increased. Scaled to field-level, our findings imply substantial economic penalties for growers, with potential losses of 175–325 USD ha−1 in Click and 500–665 USD ha−1 in Phoenix under ozone concentrations typical of spring and summer periods in Europe. Decreased total yield would likely outweigh the benefits of any improvement in animal oilseed cake quality (increased protein and key micronutrients for livestock feed). Neither cultivar sustained visible injury at earlier growth stages, and Phoenix sustained photosynthesis even under high exposure, thereby making ozone an invisible threat. Our findings of reduced oilseed quantity and quality threaten oilseed rape production, but differences between the cultivars may also offer an opportunity for breeders and agronomists to identify and exploit variation in ozone tolerance in oilseed rape

    Suitability of winter canola (Brassica napus) for enhancing summer annual crop rotations in Iowa

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    Winter canola (Brassica napus) could be a good candidate for enhancing cropping systems in Iowa because of its potential to provide environmental benefits and produce a marketable crop compatible with existing grain production and distribution schemes. However, it is still uncertain whether this crop would be suitable for helping balance environmental and financial goals of conventional cropping systems under the environmental and market conditions unique to Iowa. The work presented in this thesis is an effort to assess the suitability of winter canola for providing environmental benefits while fitting within the logistic and economic constrains of current cropping systems. Based on observations from experimentation in field plots, it is determined that canola can be successfully established in the fall, survive the winter, and regrow in the spring, but adequate conditions during fall growth are crucial. It is estimated that seeding by 31 Aug in the north to 12 Sep in the southeast will allow enough time for adequate growth of canola during the fall in at least half of the years in Iowa. Because these seeding date requirements will likely conflict with standing crops during most years, adjustments to the rotation schemes of conventional rotations are needed. Therefore, two alternative systems are proposed, and their economic profiles are studied. Findings from this economic analysis suggest that these rotation alternatives produce relatively less net returns than the conventional corn (Zea mays L.)- soybean (Glycine max (L) Merr.) rotation, throughout a range of market and canola yield scenarios. Based on these results, it is determined that although winter canola can provide some environmental and economic enhancements to summer annual crop rotations in Iowa, but the specific situations in which canola can fit these rotations are limited. Nonetheless, more research is needed to fully understand the productivity potential of winter canola in Iowa, before counting these as feasible alternatives for producers in this state

    Agronomic and physiological parameters of genotypic nitrogen efficiency in oilseed rape (Brassica napus L.)

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    [no abstract

    Daytime Summer Microclimate Influence of Large Woody Debris on Dewatered Sediments in Lake Mills, WA Following Dam Removal

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    In 2014, dam removal from the Elwha River, Washington state, exposed large areas of previously submerged sediment. The Olympic National Park placed ~100 large logs on 2 ha of exposed sediment to promote plant establishment. I quantified patterns of three microclimate variables near logs: wind speed at 10-cm height (u10), sediment temperature (TS), and evaporation rate (E); and their relationships to broader environmental factors. The northern-most log, exposed to northerly winds, was measured along 3-m perpendicular transects 14 times during August and September 2015. I determined nonlinear and multilevel regressions to investigate patterns and create models of microclimate as functions of environmental factors and distance from the log. Maximum u10 decreased to the lee. Decreases near the log occurred for u10 to the north and south, and for TS and E to the shaded north. Windward and leeward u10 models include local wind speed and distance from log. Northern TS is related to solar radiation, air temperature and distance from log. Southern TS is related to air temperature. Northern E is related to solar radiation, vapor pressure deficit and distance from log. Southern E is related to solar radiation and vapor pressure deficit. Models of southern u10 and northern TS and E were validated with data from 8 wind-protected logs, but lack of validation of the other microclimate models indicate the northern-most log has unique microclimate. Species-specific physiological information is required to predict plant reactions to near-log microclimate. All models require more data to broaden their scope

    Boron Deficiency in Soils and Crops: A Review

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    The effect of environmental factors on the physiology, yield and oil composition of safflower (Carthamus tinctorius L.)

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    This study investigated the effects of drought, nitrogen fertilizer and elevated CO2 and its interaction with nitrogen fertilizer on the physiology, growth, and production of the oil crop safflower (Carthamus tinctorius L.) in a semi-controlled glasshouse environment. Three levels of water stress were imposed: rosette (mid-season drought), stem elongation (terminal drought) and rosette to maturity (mid-season + terminal drought). Results indicated that all drought treatments imposed reduced stomatal conductance, but after the relief of mid-season drought plants recovered and as a result there were no significant differences from control in terms of yield components (branch and capital number) and seed number. Terminal drought and mid–season + terminal drought induced significant reductions in branch number (48% and 50%), in capitula number (33% and 67%), in seed number (89% and 92%), in above ground dry weight (30% and 54%) and in individual fresh seed weight (90% and 94%) respectively. However, water stress treatments had no significant effect on the maximum quantum efficiency of PSII (Fv/Fm) in dark adapted leaves compared with the control. Levels nitrogen fertilizer was studied equivalent to 0, 25, 50, 75, 100, 125, 150, 175 kg N ha-1 were evaluated. Safflower responded incrementally to increasing nitrogen applied in a curvilinear asymptotic fashion. Assimilation rate (42%), transpiration rate (32%), stomatal conductance (52%) and LAI (42%) increased III up to 100 kg N ha-1 compared with the control. The above ground dry weight and seed yield associated with WUE continued to increase with each increment in nitrogen rate and above ground dry weight (42%), individual seed fresh weight (76%) and WUE (41%) increased up to 175 kg N ha-1 compared with the control. The effect of elevated CO2, (1000 ÎŒmol mol-1) significantly increased assimilation rate (27%) reduced stomatal conductance (29%) and transpiration rate (18%), increased LAI (28%) and above ground dry weight (51%) when measured at anthesis compared with ambient (400 ÎŒmol mol-1). At the same time plant organ N content was reduced. At harvest, elevated CO2 increased above ground dry weight (42%) and individual fresh seed weight (49%). The interaction effect of elevated CO2 with nitrogen input was investigated using four nitrogen levels equivalent to 25, 75,125 and 175 kg ha-1. The nitrogen response rate was raised by elevated CO2 equally at each nitrogen application rate so that there was no significant interaction effect between the two for most parameters measured. In this way both CO2 and nitrogen were acting as “fertilizers”. Overall the results showed that despite being put forward as a drought resistant crop for low input agricultural systems safflower is capable of responding positively to well irrigate and well fertilized conditions. Furthermore under conditions of elevated CO2 it can be expected to increase its yield potential but to achieve this will require a higher degree of nitrogen fertilization. CO2 is capable of substituting for up to 100 kg N ha-1 without a decline in yield and this shows that CO2 is the primary limiting factor in safflower assimilation. IV Seed oil content and its fatty acid profile appeared to be relatively stable and were not affected drastically by either nitrogen fertilization or elevated CO2.This demonstrated the integrity of the oil filling process during seed fill and emphasized that this is primarily under genetic control with relatively little influence from environmental parameters.Iraqi Ministry of Higher Educatio

    Moistube Irrigation characterisation and yield response of canola (Brassica napus) under varied Moistube Irrigation.

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    Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Abstract available in PDF

    Effect of Spatial Arrangements of Row Spacing and Plant Density on Water Use and Water Use Efficiency of Maize Under Irrigation

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    To optimize crop water use and water use efficiency, more of the initial water resource should be routed into transpiration by reducing unproductive water losses such evaporation, drainage and runoff. In this context, a field experiment was conducted for two successive cropping seasons 2008/2009 to 2009/2010 at Kenilworth experimental station to evaluate the effect spatial arrangement of row spacings and plant density on yield and water use efficiency of maize. Three row spacing (0.225, 0.45 and 0.90 m) and five plant densities (50 000, 75 000, 100 000, 125 000 and 150 000 plants ha-1) were used. Treatments were combined in a factorial combination and laid out in a completely randomized design with replications. Spatial arrangement of row spacing and plant density had a profound impact on biomass, grain yield, water use and WUE of maize. The current investigation revealed that highest water use and mean daily ET occurred at the plant density of 125 000 plants ha-1. The interaction effect of row spacing by plant density was significant. The significantly highest biomass WUE was gained by the row spacing of 0.45 m with the plant density of 125 000 plants ha-1. Correspondingly the highest grain yield WUE was obtained from a row spacing of 0.45 m and a plant density of 100 000 plants ha-1. This was followed by a row spacing of 0.90 m at the same plant density and did not differ significantly from aforementioned. Based on this finding it could be concluded that a row spacing of 0.45 or 0.90 m with a plant density of 100 000 plants ha-1 is the optimum to be adopted for the ultra-fast maize hybrid under consideration. Keywords: Spatial arrangement, maize, water use, water use efficienc
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