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  • 34.50.H  (1)
  • 61.14F  (1)
  • Soil microbial population  (1)
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  • 1
    ISSN: 1432-0789
    Keywords: Key words Catclaw ; Carbon dioxide production ; Inorganic N dynamics ; Soil microbial population
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  In the central highlands of Mexico, heavily eroded soils are often colonized by catclaw (Mimosa buincifiera): an N2-fixing shrub. An experiment was carried out to investigate how this shrub affected characteristics of the soil and its biological functioning. Soil was sampled from outside and under the canopy of catclaw at three sites characterized by different degrees of erosion and an increase in plant density. The soil microbial biomass C, total amounts of bacteria, fungi, actinomycetes and free-living N2-fixing micro-organisms were measured, while production of CO2 and dynamics of nitrate (NO3 –), nitrite (NO2 –) and ammonium (NH4 +) were monitored in an aerobic incubation at 22±1  °C for 35 days. The C content was 1.6 times greater in the area with the largest density of plants and the least erosion (RECUP) compared with the site with the lowest density and greatest erosion (DEGR), while it was 1.2 times greater under the canopy of the catclaw than outside it (average of the three sites). The incorporation of N into the soil organic matter was greater under the canopy of the catclaw than outside it as the C:N ratio was on average 8.4 and 9. 1, respectively. The microbial biomass C, as a percentage of soil organic matter, was 1.5 times greater in the RECUP than in the DEGR site. Greatest total number of colony-forming bacteria and fungi (mean of organisms found under and outside the canopy) were found in the RECUP treatment and lowest in the DEGR treatment. Free-living N2-fixing organisms and actinomycetes showed opposite trends. Greater total numbers of colony-forming bacteria, fungi, actinomycetes and free-living N2-fixing organisms (mean of the three treatments) were found under the canopy of catclaw than outside of it, Production of CO2 was 1.8 times greater in the RECUP than in the DEGR and 1.6 times greater under the canopy of catclaw than outside. Production of NO3 – was 1.3 times greater in the RECUP than in the DEGR and 3.5 times greater under the canopy of catclaw than outside. There was no significant effect of location or canopy on NO2 – and NH4 + concentrations. It is concluded that the natural vegetation of catclaw increased microbial biomass and soil organic matter content under, but also outside its canopy, and preserved N better, releasing greater amounts of inorganic N upon mineralization. Catclaw can serve as a first colonizer of heavily eroded soil and be replaced by other vegetation, natural or crops, when fertility is restored.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-6079
    Keywords: 34.50H ; 79.20N ; 61.14F
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present detailed double differential distributions of electrons emitted downstream when 100 and 170 keV protons interact with thin carbon, gold and aluminuum foils and compare them to those obtained with protons and neutral hydrogen projectiles interacting with helium gas. The distributions obtained with the gas target show, besides the well known convoy electron peak produced by capture or loss of electrons into the continuum of the emerging ion, a narrow ridge that is aligned with the beam direction. This ridge, which is attributed to electrons moving in the two Coulomb center potential saddle determined by the target and projectile ions, also appears in the ion-solid electron distributions. A typical solid state effect consists in the appearance of two strong lateral humps which are explained as due to diffraction of the ridge electrons in the three dimensional lattice of the polycrystalline foil material. Contrarily the diffraction of convoy electrons is impeded by their strong correlation to the moving ions. In the case of the Aluminuun target the observed diffraction is typical for Al2O3. This indicates that the observed electrons originate from a thin polycrystalline oxyde layer close to the downstream surface of emission.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-6079
    Keywords: 34.50.H ; 79.20.N ; 61.14.F
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this note we correct previous evidence, according to which a structure, found in double-differential electron distributions induced by ion beam-foil interaction, could be interpreted in terms of Bragg diffraction. We now attribute this structure to a distortion of the electric field of our spectrometer and present distributions taken with a new equipment in which this distortion is eliminated.
    Type of Medium: Electronic Resource
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