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  • Dinitrogen fixation  (1)
  • Key words Leaves  (1)
  • Key words Azorhizobium caulinodans  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Biology and fertility of soils 30 (2000), S. 535-543 
    ISSN: 1432-0789
    Keywords: Key words Tree legumes ; Dinitrogen fixation ; Rhizobiology ; Timber species
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Rhizobiology of four tree legumes, Abarema bigemina (endemic), Adenanthera bicolor (endemic), Humboldtia laurifolia (indigenous) and Pericopsis mooniana (indigenous), was studied by: (1) observations of their in situ root nodulation, (2) characterization and authentication of rhizobia isolated from them, and (3) an examination of the infectivity and effectivity of the rhizobial isolates using the respective hosts and the broad-spectrum host, siratro (Macroptillium atropurpureum). Investigations were also conducted to evaluate the effect of rhizobial inoculation on growth and N fixation of the valuable timber species, P. mooniana, during its early stages of growth. All the hosts revealed in situ nodulation, except A. bicolor which had nodule-like swellings on its roots. While four rhizobial isolates were obtained from A. bigemina, four from H. laurifolia and 18 from P. mooniana, no authentic rhizobia were isolated from A. bicolor. The nodule-like structures did not show acetylene reduction activity, and the plants failed to nodulate upon inoculation with rhizosphere soil. A. bicolor was therefore tentatively assigned as a non-nodulating species. This report includes the first description of root nodules in the endemic species A. bigemina and the indigenous species H. laurifolia and the isolation and characterization of rhizobia from them. Significant differences were observed among the isolates with regard to their infectivity and effectivity. One isolate from P. mooniana was outstanding in its infectivity and effectivity on the original host, as well as on siratro. Inoculation of P. mooniana with this isolate together with a reference strain significantly improved nodulation and N fixation and gave a 50% increase in plant dry matter under a low level of N fertilizer, during a 12-month growth period. It is suggested that the nursery culture of P. mooniana could be improved by inoculation under low N-input conditions. The ability of these rhizobia to persist in the soil for a 12-month period was observed by the use of strains marked with antibiotics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0789
    Keywords: Key words Azorhizobium caulinodans ; Rice ; Inoculum survival ; Inoculum carriers ; Sesbania rostrata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Azorhizobium caulinodans strongly colonized the rhizosphere of rice plants after incorporation of Sesbania rostrata in a field trial throughout the growing season and during the fallow period until 19 weeks after incorporation of S. rostrata. A. caulinodans became well established in the rhizosphere (7.17 log cfu g–1 dry rice root) and colonized subsequent S. rostrata test plants. Three traditional and three improved high-yielding rice varieties were inoculated with A. caulinodans under gnotobiotic conditions. In none of the combinations did acetylene reduction activity significantly increase. Ethylene production on colonized rice roots only started after the growth medium had been supplemented with an extra C source (0.1 to 0.25% Na-lactate). This indicates that the bacterial nitrogenase activity is limited by energy supply. Four possible inoculant-carriers (peat, coir dust, bagasse, rice straw) were compared for long-term survival of the bacterial strain. Independent of the storage temperature (26  °C or 4  °C), the survival of A. caulinodans in peat and coir dust was very high during a 12-month period (〉8 log cfu g–1 dry carrier), whereas the bagasse and rice straw carriers showed a serious decline from 3 months onwards.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Biology and fertility of soils 26 (1997), S. 136-140 
    ISSN: 1432-0789
    Keywords: Key words Leaves ; Low moisture ; Decomposition ; Nitrogen release
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract During the dry season in the tropics, agriculture which is solely dependent upon rainfall as its source of water is frequently affected by soil moisture stress, resulting in crop failures. Farmers therefore depend mainly on other sources of limited water supply during this period, such as ground water. Soil moisture conservation measures, especially surface mulching with loppings and, occasionally, leaf litter and crop residues, are practised. Our objective was to study the decomposition and nitrogen (N) release from these plant materials under continuously wet, low moisture regimes, i.e. comparable to those which prevail in the mulches used in the agriculture. A greenhouse experiment was conducted with fresh, chopped leaves of six leguminous trees, wild sunflower and rice, which were spread as a mulch on a layer of soil. They were maintained at eight moisture levels (a total of between zero and 43l water m–2 applied over 8 weeks) by spraying water. Different optimal moisture requirements for the rapid decomposition of these species were observed. These were presumably determined by different physical and chemical properties of the leaves. The amount of water received to the mulches and their soluble polyphenolic and carbon (C) concentrations played an important role in determining the decomposition and the mode of N release under non-limiting conditions of leaf N. Specifically, the C concentration governed N release, while the effect of polyphenolics was important when their concentration was low, as a result of leaching under relatively high moisture regimes. Leaves with a high polyphenolic and C content, which were subjected to high leaching losses of these fractions, underwent a change in their N dynamics from net immobilization to mineralization. This study indicates that leaves with a fast rate of decomposition should be mixed with other species, leaves which decompose more slowly in order to increase the conservation of soil moisture and also improve the synchronization between N release from the mulch and its demand by crops.
    Type of Medium: Electronic Resource
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