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  • 1
    ISSN: 1432-0789
    Keywords: Nitrogen mineralization ; Sandy soils ; Organic-bound nitrogen ; electro-ultrafiltration method CaCl2 method ; Ammonium ; Nitrate ; N uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Sandy soils have low reserves of mineral N in spring. Therefore organic-bound N is the most important pool available for crops. The objective of the present investigation was to study the importance of the organic-bound N extracted by electro-ultrafiltration and by a CaCl2 solution for the supply of N to rape and for N mineralization. Mitscherlich-pot experiments carried out with 12 different sandy soils (Germany) showed a highly significant correlation between the organic N extracted (two fractions) and the N uptake by the rape (electroultrafiltration extract: r=0.76***; CaCl2 extract: r=0.76***). Organic N extracted by both methods before the application of N fertilizer was also significantly correlated with N mineralization (electro-ultrafiltration extract: r=0.75***; CaCl2 extract: r=0.79***). N uptake by the rape and the mineralization of organic N increased with soil pH and decreased with an increasing C:N ratio and an increasing proportion of sand in the soils. Ninety-eight percent of the variation in N uptake by the rape was determined by the differences in net mineralization of organic N. This show that in sandy soils with low mineral N reserves (NO inf3 sup- -N, NH 4 + -N) the organic soil N extracted by electro-ultrafiltration or CaCl2 solutions indicates the variance in plant-available N. Total soil N was not related to the N uptake by plants nor to N mineralization.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Biology and fertility of soils 23 (1996), S. 314-320 
    ISSN: 1432-0789
    Keywords: Key words Nitrogen mineralization ; Microbial biomass ; Soil drying ; Extractable organic N ; 15N isotope dilution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A laboratory soil incubation and a pot experiment with ryegrass were carried out in order to examine the extractability of microbial biomass N by using either 10-mM CaCl2 extraction or the electro-ultrafiltration (EUF) method. The aim of the experiment was to test the hypothesis whether the organic N (Norg) extracted by EUF or CaCl2 from dried soil samples represents a part of the microbial biomass. For the laboratory incubation a 15N-labelled Escherichia coli suspension was mixed with the soil. For the pot experiment a suspension of 15N-labelled bacteria was applied which had previously been isolated from the soil used. Soil samples of both treatments, with and without applied bacterial suspension, were extracted by EUF and CaCl2. The extractability of applied microbial biomass was estimated from the difference in extractable Norg between the two treatments. In addition, the N isotopic composition in the upper plant matter, in the soil, and in organic and inorganic N fractions of EUF and CaCl2 extracts was analysed. Both experiments showed that the applied microbial biomass was highly accessible to mineralization and thus represented potentially mineralizable N. However, this mineralizable N was not extractable by CaCl2 or by the EUF method. It was, therefore, concluded that the organic N released on soil drying and which was thus extractable was derived from the non-biomass soil organic matter. The result suggests that both extraction methods may provide a suitable index for mineralizable N only in cases where the decomposable organic substrates are derived mainly from sources other than the living soil biota.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Biology and fertility of soils 23 (1996), S. 314-320 
    ISSN: 1432-0789
    Keywords: Nitrogen mineralization ; Microbial biomass ; Soil drying ; Extractable organic N ; 15N isotope dilution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A laboratory soil incubation and a pot experiment with ryegrass were carried out in order to examine the extractability of microbial biomass N by using either 10-mM CaCl2 extraction or the electro-ultrafiltration (EUF) method. The aim of the experiment was to test the hypothesis whether the organic N (Norg) extracted by EUF or CaCl2 from dried soil samples represents a part of the microbial biomass. For the laboratory incubation a 15N-labelled Escherichia coli suspension was mixed with the soil. For the pot experiment a suspension of 15N-labelled bacteria was applied which had previously been isolated from the soil used. Soil samples of both treatments, with and without applied bacterial suspension, were extracted by EUF and CaCl2. The extractability of applied microbial biomass was estimated from the difference in extractable Norg between the two treatments. In addition, the N isotopic composition in the upper plant matter, in the soil, and in organic and inorganic N fractions of EUF and CaCl2 extracts was analysed. Both experiments showed that the applied microbial biomass was highly accessible to mineralization and thus represented potentially mineralizable N. However, this mineralizable N was not extractable by CaCl2 or by the EUF method. It was, therefore, concluded that the organic N released on soil drying and which was thus extractable was derived from the non-biomass soil organic matter. The result suggests that both extraction methods may provide a suitable index for mineralizable N only in cases where the decomposable organic substrates are derived mainly from sources other than the living soil biota.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Biology and fertility of soils 30 (2000), S. 328-332 
    ISSN: 1432-0789
    Keywords: Key words Nitrate-N ; Ammonium-N ; Organic bound N ; N-extraction methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Improving the precision in estimating the nitrogen (N) requirement for citrus trees on sandy soils is important for increasing N efficiency by the trees and minimizing potential losses of N in commercial citrus production areas. In this study, representative Florida soils were sampled from major citrus production areas and the electro-ultrafiltration (EUF) technique was used to measure the concentrations of total EUF-extractable nitrogen (EUF-Nt), ammonium-N (EUF-NH4 +–N) and nitrate-N (EUF-NO3 ––N). Available organic N (Norg) was calculated as: EUF-Nt–(NH4 +–N+NO3 ––N). The N concentrations in the EUF extraction were greater than those by the KCl or CaCl2 method. The Norg fraction, estimated by the EUF method, varied from 4.4 to 40.8 mg kg–1 soil, equivalent to 10 to 91 kg N ha–1 (for the top 15 cm depth soil) and was positively correlated with the total soil N determined by the Kjeldahl method. The presence of appreciable amounts of Norg in these soils indicates that these soils contain high proportions of the total soil N in easily mineralizable Norg forms. This study demonstrates that the EUF-extractable organic bound N must be considered in developing N fertilizer recommendations for citrus.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1434-3940
    Keywords: Schlüsselwörter CT ; MRT ; Mundhöhlen- und Oropharynxtumoren ; Diagnose ; Tumorstaging ; Keywords CT ; MRI ; Head and neck tumors ; Diagnosis ; Staging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Problem: There is a lack of clear criteria for the use of MR and CT in the diagnosis of head and neck cancer – some of it is even contradictory. The results of this study should lead to the establishment of more clear criteria. Patients: 165 patients suffering from head and neck tumors were subjected to a total of 463 CT and 197 MRI examinations. Results: The CT and MRI staging corresponded in 67% and 60% of the oropharynx tumors, respectively, with the clinical findings. In the case of oral cavity tumors, the clinical TNM stages were identical with CT and MRI results in 50% and 43% of cases, respectively. In the case of lymphatic node staging, the frequency of error was slightly higher using MRI, at 27%, compared with the CT rate of 22%. In the evaluation of cervical lymphatic nodes, CT proved to be more sensitive attaining 78% compared to the MRI rate of 69%. Conclusion: The results provide clear indications as to the MRI and CT examinations. Primary preoperative screening and post-therapeutic aftercare should be assessed using CT, as should lymphatic node diagnosis in the neck area. In the case of special problems such as, for example, the relevant bone and periostium infiltration, MR should be considered as a supplementary examination at a second stage.
    Notes: Fragestellung: Die Differenzialindikation von MRT und CT bei der Diagnostik von Malignomen im Kopf-Hals-Bereich wird in der Literatur kontrovers diskutiert. Mit der vorliegenden Studie soll versucht werden, eine eindeutige Auswahl des Verfahrens zu begründen. Patientengut: Bei 165 Patienten mit Tumoren des Oropharynx und der Mundhöhle wurden insgesamt 463 CT- und 197 MRT-Untersuchungen durchgeführt. Ergebnisse: Bei 67% bzw. 60% der Oropharynxtumoren stimmten das CT- bzw. MRT-TNM-Tumorstaging mit der Klinik überein. Bei den Mundhöhlentumoren waren die klinischen TNM-Stadien in 50% bzw. 43% mit den CT- bzw. MRT-Befunden identisch. Beim Lymphknotenstaging war die Fehlerhäufigkeit bei der MRT mit 27% etwas höher als bei der Computertomographie mit 22%. Bei der Beurteilung der zervikalen Lymphknoten war die CT der MRT bezüglich der Sensitivität mit 78% gegenüber 69% überlegen. Schlussfolgerung: Aufgrund der Ergebnisse ergeben sich eindeutige Indikationen zur MRT- und CT-Untersuchung. Das primäre präoperative Screening und die posttherapeutische Nachsorge sollten durch CT beurteilt werden ebenso wie die Lymphknotendiagnostik im Halsbereich. Bei speziellen Fragestellungen, wie z. B. bezüglich der Periost- und Knocheninfiltration, ist die MRT eine ergänzende Untersuchung des 2. Schritts.
    Type of Medium: Electronic Resource
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