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  • GEOPHYSICS  (3)
  • Lolium perenne  (3)
  • Trifolium repens  (3)
  • 1
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    Investigation of the association of magnetopause instability with interplanetary sector structure (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The variation of the solar wind parameters (speed, magnetic field intensity, and proton density) and geomagnetic disturbance with location within the interplanetary sector structure is well established. The Kelvin-Helmholtz instability of the magnetopause provides a mechanism for the initiation of worldwide geomagnetic disturbance. Since the Kelvin-Helmholtz mechanism depends on an integration of several of the solar wind parameters, it was considered of interest to see how it varies within the sector structure. Support is given to the idea that the integration of the solar wind parameters via Kelvin-Helmholtz instability is an important concept in understanding geomagnetic disturbance.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 79; Feb. 1
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Explorer 18 study of the stability of the magnetopause using a Kelvin-Helmholtz instability criterion (1973)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Explorer 18 magnetometer and plasma probe data are used to calculate the magnitude of the Kelvin-Helmholtz instability criterion for 42 crossings of the magnetopause. The 30 crossings through the dipole field region show that for low levels of geomagnetic disturbance ( Kp less than or equal to 2) large regions of the magnetopause near the nose are stable, whereas for higher levels of geomagnetic disturbance (Kp greater than 2) only a small region near the nose is stable. The unstable regions are found further downstream. Similarly, the 12 crossings through the tail show that the unstable regions are downstream of the stable regions. The Kelvin-Helmholtz mechanism might be the 'viscous interaction' discussed by Axford and Hines (1961) and the relevant parameter for worldwide geomagnetic disturbance, just as the southward interplanetary field has been firmly established as the major relevant parameter in the case of substorm activity.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 78; Dec. 1
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Kelvin-Helmholtz instability and the semiannual variation of geomagnetic activity (1970)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Kelvin-Helmholtz instability at magnetopause, initiating semiannual variation of geomagnetic disturbances
    Keywords: GEOPHYSICS
    Type: SYMPOSIUM ON INSTABILITIES IN THE MAGNETOSPHERE; Sep 01, 1969 - Sep 12, 1969; MADRID; SPAIN|; ADEMIE DES SCIENCES
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
    Electronic Resource
    Electronic Resource
    Nitrogen fixation by white clover when competing with grasses at moderately low temperatures (1991)
    Springer
    Plant and soil 133 (1991), S. 47-56 
    Details
    ISSN: 1573-5036
    Keywords: clover ; competition ; grass ; Lolium perenne ; 15N ; nitrogen fixation ; Phleum pratense ; temperature ; Trifolium repens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract It was the aim of this study to determine the way in which low temperature modifies the effect of a competing grass on nitrogen fixation of a forage legume. White clover (Trifolium repens L.) was grown in monoculture or in different planting ratios with timothy (Phleum pratense L.) or perennial ryegress (Lolium perenne L.) in growth chambers at either 7.5/5°C (LoT) or 15/10°C (HiT) average day/night temperatures, and with 2.5 or 7.5 mM 15N-labelled nitrate in the nutrient solution. Competition with grass led to a marked increase in the proportion of clover nitrogen derived from symbiosis (% Nsym). This increase was slower at LoT where % Nsym was reduced considerably; it was closely related to the reduction in the amount of available nitrate as a result of its being utilized by the grass. Nitrogen concentration in white clover herbage and dry matter yield per clover plant were reduced, for the most part, when a competing grass was present. The amount of nitrogen fixed per plant of white clover decreased markedly with temperature. Low temperature consequently accentuated competition for nitrate. The capacity of white clover to compete successfully was limited by its slower growth and nitrogen accumulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00011898
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  • 5
    Electronic Resource
    Electronic Resource
    Symbiotically fixed nitrogen from field- grown white and red clover mixed with ryegrasses at low levels of15N-fertilization (1987)
    Springer
    Plant and soil 104 (1987), S. 219-226 
    Details
    ISSN: 1573-5036
    Keywords: clover ; legume/grass mixture ; Lolium multiflorum ; Lolium perenne ; 15N ; nitrogen fixation ; nitrogen transfer ; Trifolium pratense ; Trifolium repens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A field study was carried out near Zürich (Switzerland) to determine the yield of symbiotically fixed nitrogen (15N dilution) from white clover (Trifolium repens L.) grown with perennial ryegrass (Lolium perenne L) and from red clover (Trifolium pratense L.) grown with Italian ryegrass (Lolium multiflorum Lam.). A zero N fertilizer treatment was compared to a 30 kg N/ha per cut regime (90 to 150 kg ha−1 annually). The annual yield of clover N derived from symbiosis averaged 131 kg ha−1 (49 to 227 kg) without N fertilization and 83 kg ha−1 (21 to 173 kg) with 30 kg of fertilizer N ha−1 per cut in the seeding year. Values for the first production year were 308 kg ha−1 (268 to 373 kg) without N fertilization and 232 kg ha−1 (165 to 305 kg) with 30 kg fertilizer N ha−1 per cut. The variation between years was associated mainly with the proportion of clover in the mixtures. Apparent clover-to-grass transfer of fixed N contributed up to 52 kg N ha−1 per year (17 kg N ha−1 on average) to the N yield of the mixtures. Percentage N derived from symbiosis averaged 75% for white and 86% for red clover. These percentages were affected only slightly by supplemental nitrogen, but declined markedly during late summer for white clover. It is concluded that the annual yield of symbiotically fixed N from clover/grass mixtures can be very high, provided that the proportion of clover in the mixtures exceeds 50% of total dry mass yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02372535
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  • 6
    Electronic Resource
    Electronic Resource
    Influence of dissimilarities in temporal and spatial N-uptake patterns on15N-based estimates of fixation and transfer of N in ryegrass-clover mixtures (1988)
    Springer
    Plant and soil 112 (1988), S. 167-175 
    Details
    ISSN: 1573-5036
    Keywords: clover ; Lolium multiflorum ; Lolium perenne ; 15N ; N-uptake ; nitrogen transfer ; nitrogen fixation ; Trifolium repens ; Trifolium pratense
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The temporal N-uptake patterns of white clover (Trifolium repens L.) mixed with perennial ryegrass (Lolium perenne L.) and of red clover (Trifolium pratense L.) mixed with Italian ryegrass (Lolium multiflorum Lam.) were determined in successive harvests of herbage within the growth cycles of a ley established near Zürich (Switzerland). Rooting patterns were examined by injecting15N-fertilizer at soil depths ranging from 10 to 40 cm. The results were analyzed to determine the effect of variations in time and depth of N-uptake on the15N-based measurement of N from symbiosis (Nsym) and N from transfer (Ntrans). Grasses in mixture appeared to have deeper rooting systems than grass monocultures, which led to an overestimation of N transfer from white clover to perennial ryegrass if15N was spread on the soil surface. White clover generally lagged behind grass in soil N- uptake. Soil N-uptake of red clover slowed down before that of the grass because % Nsym almost reached 100% during the second half of each growth cycle. However, the effect of these dissimilarities on the seasonal average of %Nsym did not exceed 2%. It is concluded that at the observed high levels of N2 fixation, failure to account for the N-uptake patterns of the test and reference crops only slightly affected the estimates of % Nsym and % Ntrans, and did not invalidate the observed differences between species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02139992
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