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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis of 15N-labelled microbial biomass in soil in situ and extraction of biomass N (1989)
    Springer
    Biology and fertility of soils 7 (1989), S. 180-185 
    Details
    ISSN: 1432-0789
    Keywords: Extractability ratios ; Microbial biomass ; N immobilization-remineralization ; Priming effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A Pakistani soil (Hafizabad silt loam) was incubated at 30°C with varying levels of 15N-labelled ammonium sulphate and glucose (C/N ratio of 30 at each addition rate) in order to generate different insitu levels of 15N-labelled microbial biomass. At a stage when all of the applied 15N was in organic forms, as biomass and products, the soil samples were analysed for biomass N by the chloroform (CHCl3) fumigation-extraction method, which involves exposure of the soil to CHCl3 vapour for 24 h followed by extraction with 500 mM K2SO4. A correction is made for inorganic and organic N in 500 mM K2SO4 extracts of the unfumigated soil. Results obtained using this approach were compared with the amounts of immobilized 15N extracted by 500 mM K2SO4 containing different amounts of CHCl3. The extraction time varied from 0.5 to 4 h. The amount of N extracted ranged from 27 to 270 μg g−1, the minimum occurring at the lowest (67 μg g−1) and the maximum at the highest (333 μg g−1) N-addition rate. Extractability of biomass 15N ranged from 25% at the lowest N-addition rate to 65%a for the highest rate and increased consistently with an increase in the amount of 15N and glucose added. The amounts of both soil N and immobilized 15N extracted with 500 mM K2SO4 containing CHCl3 increased with an increase in extraction time and in concentration of CHCl3. The chloroform fumigation-extraction method gives low estimates for biomass N because some of the organic N in K2SO4 extracts of unfumigated soil is derived from biomass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00292580
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  • 2
    Electronic Resource
    Electronic Resource
    Transformation of 15N-labelled leguminous plant material in three contrasting soils (1989)
    Springer
    Biology and fertility of soils 8 (1989), S. 54-60 
    Details
    ISSN: 1432-0789
    Keywords: Biomass N ; Humus fractions ; Hydrolyzable N ; Legume N ; Mineralizable N ; N-mineralization ; 15N-labelled material
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Two soils from Pakistan (Hafizabad silt loam and Khurrarianwala silt loam) and one from Illinois, USA (Drummer silty clay loam) were incubated with 15N-labelled soybean tops for up to 20 weeks at 30°C. Mineralization of soybean 15N was slightly more rapid in the Pakistani soils, and after 20 weeks of incubation, 50%, 53%, and 56% of the applied 15N was accounted for as (NH4 ++NO3 −)-N in Drummer, Hafizabad, and Khurrarianwala soils, respectively. Potentially mineralizable N (determined by anaerobic incubation) varied between 1.5% and 10% of the applied 15N in the three soils at different stages of incubation; somewhat higher percentages were mineralizable in the Pakistani soils than in the Drummer soil. From 3.7% to 9% of the applied 15N was accounted for in the microbial biomass. From 10% to 32% of the applied N was recovered in the humic acid and fulvic acid fractions of the organic matter by sequential extraction with Na4P2O7 and NaOH; from 12% to 49% was recovered in the humin fraction. Of the three soils, Drummer soil contained more 15N as humic and fulvic acids. In all cases, the 15N was approximately equally distributed between the humic and fulvic acid fractions. A significant percentage of the humin 15N (52%–78%, equivalent to 8%–34% of the applied 15N) occurred in non-hydrolyzable (6 N HCl) forms. Of the hydrolyzable 15N, 42%–51% was accounted for as amino acid-N followed in order by NH3 (17%–30%), hydrolyzable unknown forms (20%–22%), and amino sugars (6%–2%). The recovery of applied 15N for the different incubation stages was 87±22%. Recovery was lowest with the Khurrarianwala soil, presumably because of NH3 volatilization losses caused by the high pH of this soil.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00260516
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  • 3
    Electronic Resource
    Electronic Resource
    Transformations of chemically fixed liquid anhydrous ammonia by soil microorganisms (1991)
    Springer
    Biology and fertility of soils 11 (1991), S. 145-150 
    Details
    ISSN: 1432-0789
    Keywords: Nitrogen-15 ; Ammonia fixation ; Organic matter-fixed NH3 ; Clay-fixed NH inf4 sup+
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The application of liquid anhydrous NH3 to soil leads to chemical fixation of NH3 by organic matter and of NH inf4 sup+ by clay minerals. A laboratory study was conducted to ascertain the biological transformations of newly fixed liquid anhydrous 15NH3 in a Drummer silty clay loam by incubation of the 15N-labelled soil with glucose for 0, 7, 30, and 90 days and by sequential extraction of organic-matter-fixed 15NH3 with 0.15 M Na4P2O7, 0.15 M KOH, 0.1 M NaOH, and acidified dimethyl sulfoxide. About 16% of the 15NH3 injected was fixed, of which 52% was accounted for by clay fixation. The various humic fractions (fulvic acid, humic acid, and humin) were obtained, and the distribution patterns of the fixed 15NH3-N in these fractions were compared. The potential availability of the fixed 15NH3-N was also estimated. The percentage of the 15NH3 recovered as organic-matter-fixed 15NH3 decreased as the length of incubation increased (to 28% after 90 days); the decrease was attributed in part to an increase in the amount recovered as clay-fixed NH inf4 sup+ (from 52 to 64%). Changes in the distribution of the organic-matter-fixed 15NH3-N in the humic fractions included: (1) an increase in the relative amount of the fixed 15NH3 as humic acid in both the Na4P2O7 and KOH extracts, (2) an increase in the percentage of organic-matter-fixed 15NH3-N in the fulvic acid fractions as high-molecular-weight components (determined by dialysis) or as generic fulvic acid (determined by sorption-desorption from XAD-8 resin), and (3) an increase in the percentage of the organic-matter-fixed 15NH3 as humin. The potential availability of the organic-matter-fixed 15NH3-N decreased as the length of the incubation increased, from 22 to 4% over the 90-day incubation period, and was correlated significantly (0.05 level) with Na4P2O7-extractable N. These results suggest that organic-matter-fixed liquid anhydrous NH3 is initially more labile than the native soil N but becomes less labile with time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336380
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  • 4
    Electronic Resource
    Electronic Resource
    Nitrogen fertilizers promote denitrification (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 211-220 
    Details
    ISSN: 1432-0789
    Keywords: Key words Denitrification ; Fertilizer efficiency ; 15N ; Labelled dinitrogen ; Nitrification ; Nitrous oxide ; Urea ; Waterlogged soil ; Water-soluble organic carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A laboratory study was conducted to compare the effects of different N fertilizers on emission of N2 and N2O during denitrification of NO3 – in waterlogged soil. Field-moist samples of Drummer silty clay loam soil (fine-silty, mixed, mesic Typic Haplaquoll) were incubated under aerobic conditions for 0, 2, 4, 7, 14, 21, or 42 days with or without addition of unlabelled (NH4)2SO4, urea, NH4H2PO4, (NH4)2HPO4, NH4NO3 (200 or 1000 mg N kg–1 soil), or liquid anhydrous NH3 (1000 mg N kg–1 soil). The incubated soil samples were then treated with 15N-labelled KNO3 (250 mg N kg–1 soil, 73.7 atom% 15N), and incubation was carried out under waterlogged conditions for 5 days, followed by collection of atmospheric samples for 15N analyses to determine labelled N2 and N2O. Compared to samples incubated without addition of unlabelled N, all of the fertilizers promoted denitrification of 15NO3 –. Emission of labelled N2 and N2O decreased in the order: Anhydrous NH3〉urea〈$〉\gg〈$〉 (NH4)2HPO4〉(NH4)2SO4≃NH4NO3≃NH4H2PO4. The highest emissions observed with anhydrous NH3 or urea coincided with the presence of NO2 –, and 15N analyses indicated that these emissions originated from NO2 – rather than NO3 –. Emissions of labelled N2 and N2O were significantly correlated with fertilizer effects on soil pH and water-soluble organic C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050233
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  • 5
    Electronic Resource
    Electronic Resource
    Immobilization of ammonium and nitrate and their interaction with native N in three Illinois Mollisols (1993)
    Springer
    Biology and fertility of soils 15 (1993), S. 50-54 
    Details
    ISSN: 1432-0789
    Keywords: Mollisol ; N interaction ; N availability ; N fertilizers ; N immobilization ; N mineralization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Three Illinois Mollisols were incubated for 2 weeks at 25°C after treatment with different amounts of glucose and/or 15N-labelled (NH4)2SO4 or 15N-labelled KNO3. The objectives were: (1) to compare the immobilization and interaction of NH inf4 sup+ −N and NO inf3 sup- −N with the native soil N, and (2) to study the relationship between immobilization of applied N and the added N interaction. As determined, immobilized N refers to forms not extractable with 2 MKCl (immobilized 15N+clay-fixed 15NH inf4 sup+ ). In all cases, both NH inf4 sup+ −N and NO inf3 sup- −N were actively immobilized and transformed into organic forms in the presence of glucose. In the absence of glucose, a higher proportion of NH inf4 sup+ than NO inf3 sup- was recovered in organic forms. Although the three soils differed considerably in the amounts of applied N immobilized, similar trends in N immobilization were observed. A positive added N interaction occurred with all soils, the magnitude increasing with the rate of N addition. In the absence of glucose, higher added N interactions were obtained for NH inf4 sup+ than NO inf3 sup- , whereas there was very little difference between NH inf4 sup+ and NO inf3 sup- in the presence of glucose. The results indicate that under conditions of rapid immobilization (e.g., in the presence of glucose), NH inf4 sup+ and NO inf3 sup- will show comparable interaction with the native soil N, whereas in unamended soil, the extent of this interaction will be greater with NH inf4 sup+ than with NO inf3 sup- . Significant correlations were observed between applied N immobilized and the added N interaction only in one soil having a high initial mineral N content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336288
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of ammonium fixation and displacement on the added nitrogen interaction in incubation experiments (1994)
    Springer
    Biology and fertility of soils 18 (1994), S. 99-102 
    Details
    ISSN: 1432-0789
    Keywords: Added N interaction ; Ammonium fixation ; N immobilization ; N mineralization ; Priming effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A laboratory incubation experiment was conducted to study the effect of NH 4 + fixation/defixation on the added N interaction (ANI) in three Illinois Mollisols fertilized with 100 or 200 mg N kg-1 soil. A positive ANI was observed in all three soils, which was greater at the higher rate of applied N. However, very little exchange was observed between applied 15NH 4 + and the native clay-fixed NH 4 + , and the ANI observed were attributed largely to microbial immobilization-mineralization. The results suggested that variations in the NH 4 + fixation capacity of soils will not have a significant bearing on the interpretation of data obtained from studies of the ANI.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336453
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  • 7
    Electronic Resource
    Electronic Resource
    Quantification and potential availability of non-symbiotically fixed 15N in soil (1988)
    Springer
    Biology and fertility of soils 7 (1988), S. 32-38 
    Details
    ISSN: 1432-0789
    Keywords: Hydrolysable N ; Mineralizable N ; N2-fixation ; Priming effect ; Plant available N
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Non-symbiotic N2 fixation was studied under laboratory conditions in two soils from Pakistan (Hafizabad silt loam and Khurrarianwala silt loam) and one from Illinois, USA (Drummer silty clay loam) incubated in a 15N-enriched atmosphere. N2 fixation was greatest with the Drummer soil (18–122 μg g−1 soil, depending upon the soil treatment) and lowest with the Khurrarianwala soil (4–81 μg g−1 soil). Fixation was increased by the addition of glucose, a close correlation being observed between the amount of glucose added and the amount of N2 fixed in the three soils (r = 0.96). Efficiency of N2 fixation varied with soil type and treatment and was greatest in the presence of added inorganic P. Application of Mo apparently had a negative effect on the amount and efficiency of N2 fixation in all the soils. The percentage of non-symbiotically fixed 15N in potentially mineralizable form (NH 4 + -N released in soil after a 15-day incubation period under anaerobic conditions) was low (2%–18%, depending upon the soil treatment), although most of the fixed N (up to 90%) was recovered as forms hydrolysable with 6N HCl. Recovery in hydrolysable forms was much greater for the fixed N than for the native soil N, indicating that the former was more available for uptake by plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00260729
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  • 8
    Electronic Resource
    Electronic Resource
    Southern Ocean sea-ice extent, productivity and iron flux over the past eight glacial cycles (2007)
    [s.l.] : Nature Publishing Group
    Nature 449 (2007), S. 748-748 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Nature 440, 491–496 (2006); doi:10.1038/nature04614. In calculating the fluxes used in this paper, we made a mistake in the snow accumulation rate used. We calculated fluxes assuming that snow accumulation rates were expressed in metres ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature06271
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  • 9
    Electronic Resource
    Electronic Resource
    Southern Ocean sea-ice extent, productivity and iron flux over the past eight glacial cycles (2006)
    [s.l.] : Nature Publishing Group
    Nature 440 (2006), S. 491-496 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Sea ice and dust flux increased greatly in the Southern Ocean during the last glacial period. Palaeorecords provide contradictory evidence about marine productivity in this region, but beyond one glacial cycle, data were sparse. Here we present continuous chemical proxy data spanning the last eight ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature04614
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  • 10
    Electronic Resource
    Electronic Resource
    A commercial system for automated nitrogen isotope-ratio analysis by the Rittenberg technique (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 897-903 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A sequential sample treatment system is described that permits use of an isotope-ratio mass spectrometer for automated Rittenberg analyses of ammonium salts. This system is based on the design of McInteer and Montoya [Recent Developments in Mass Spectrometry in Biochemistry, Medicine and Environmental Research, edited by A. Frigerio (Elsevier, Amsterdam, 1981), Vol. 7, p. 343]. An x-y table and a set of valves under computer control are used to automatically perform hypobromite oxidations, introduce the N2 thus liberated to the mass spectrometer for isotope-ratio analysis, and effect spent sample pumpaway. Analyses can be performed on samples containing 20 μg of N. When operated with a Nuclide Model 3-60-RMS double-collector mass spectrometer, the standard deviation for measurements at the natural abundance level (12 samples, 50 or 100 μg of N per sample) ranged from 0.0002 to 0.000 06 at. % 15N. Throughput capacity is 100–250 samples per day, and unattended operation can continue for at least three days.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141460
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