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  • 1
    Electronic Resource
    Electronic Resource
    Effect of inoculation ofAzospirillum spp. on nitrogen accumulation by field-grown wheat (1986)
    Springer
    Plant and soil 95 (1986), S. 109-121 
    Details
    ISSN: 1573-5036
    Keywords: Azospirillum amazonense ; A. brasilense ; N NR− mutant ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Two experiments were performed to examine the effects of inoculation of field grown wheat with various Azospirillum strains. In the first experiment the soil was sterilized with methyl bromide to reduce the Azospirillum population and15N labelled fertilizer was added to all treatments. Two strains ofAzospirillum brasilense isolated from surface sterilized wheat roots and theA. brasilense type strain Sp7 all produced similar increases in grain yield and N content. From the15N and acetylene reduction data it was apparent that these increases were not due to N2 fixation. In the second experiment performed in the same (unsterilized) soil, twoA. brasilense strains (Sp245, Sp246) and oneA. amazonense strain (Am YTr), all isolated from wheat roots, produced responses of dry matter and N content while the response to the strain Sp7 was much smaller. These data confirm earlier results which indicate that if natural Azospirillum populations in the soil are high (the normal situation under Brazilian conditions), strains which are isolated from wheat roots are better able to produce inoculation responses than strains isolated from other sources. The inoculation of a nitrate reductase negative mutant of the strain Sp245 produced only a very small inoculation response in wheat. This suggests that the much greater inoculation response of the original strain was not due to N2 fixation but to an increased nitrate assimilation due to the nitrate reductase activity of the bacteria in the roots.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02378857
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  • 2
    Electronic Resource
    Electronic Resource
    Field application of the15N isotope dilution technique for the reliable quantification of plant-associated biological nitrogen fixation (1995)
    Springer
    Nutrient cycling in agroecosystems 42 (1995), S. 77-87 
    Details
    ISSN: 1573-0867
    Keywords: biological nitrogen fixation ; control crops ; isotope dilution technique ; legumes ; 15N slow-release fertilizer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract To apply the isotope dilution (ID) technique, it is necessary to grow the “N2-fixing” crop in a soil where the mineral N is labelled with15N. Normally the “N2-fixing” crop and a suitable non-N2-fixing control crop are grown in the same labelled soil and the15N enrichment of the control crop is assumed to be equal to the15N enrichment of the nitrogen (N) derived from the soil in the “N2-fixing” crop. In this case the proportion of unlabelled N being derived from the air via biological N2 fixation (BNF) in the “N2-fixing” crop will be proportional to the dilution of the enrichment of the N derived from the labelled soil. To label the soil, the technique most often used is to add a single addition of15N-labelled N fertilizer shortly before, at, or shortly after, the planting of the crops. Data in the literature clearly show that this technique results in a rapid fall in the15N enrichment of soil mineral N with time. Under these conditions, if the control and the “N2-fixing” crops have different patterns of N uptake from the soil they will inevitably obtain different15N enrichments in the soil-derived N. In this case the isotope dilution technique cannot be applied, or if it is, there will be an error introduced into, the estimate of the contribution of N derived from BNF. Several experiments are described which explore different strategies of application of the ID technique to attempt to attenuate the errors involved. The results suggest that it is wise to use slow-release forms of labelled N, or in some cases, multiple additions, to diminish temporal changes in the15N enrichment of soil mineral N. The use of several control crops produces a range of different estimates of the BNF contributions to the “N2-fixing” crops, and the extent of this range gives a measure of the accuracy of the estimates. Likewise the use of more than one15N enrichment technique in the same experiment will also give a range of estimates which can be treated similarly. The potential of other techniques, such as sequential harvesting of both control and test crops, are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00750501
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  • 3
    Electronic Resource
    Electronic Resource
    Estimation of the contribution of biological N2 fixation to twoPhaseolus vulgaris genotypes using simulation of plant nitrogen uptake from15N-labelled soil (1995)
    Springer
    Nutrient cycling in agroecosystems 45 (1995), S. 169-185 
    Details
    ISSN: 1573-0867
    Keywords: 15N ; non-nod beans ; quantification of N2 fixation ; reference crops ; simulation technique ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A technique for the application of the15N isotope dilution technique for the quantification of plant associated biological nitrogen fixation (BNF) was tested and applied to quantify the BNF contribution to two genotypes ofPhaseolus vulgaris. The technique makes use of sequential measurements of the15N enrichment of soil mineral N, and the uptake of labelled N by the “N2-fixing” plant, to simulate its uptake of soil N (the “soil to plant simulation” technique). The test was made with two non-N2-fixing crops (non-nodulating beans and wheat) and two bean genotypes (PR 923450 and Puebla 152), at two levels of N fertilizer addition (10 and 40 kg N ha−1), to compare the actual N uptake with that simulated from the soil and crop15N data. The simulation of the soil N uptake by the non-nod bean crop using this “soil to plant simulation” technique underestimated by 20 to 30% the true N uptake, suggesting that the mineral N extracted from soil samples taken from the 0–15cm layer had a higher15N enrichment than that N sampled by the roots of this crop. In the case of the wheat crop the simulation resulted in a much greater underestimation of actual N uptake. In general the results using this technique suggested that BNF inputs to the bean cultivars was higher than would be expected from the nodulation and acetylene reduction data, except for the early PR beans in the 40 kg N ha−1 treatment. In this case the total N and simulated soil N accumulation were well matched suggesting no BNF inputs. An allied technique (the “plant to plant simulation technique”) was proposed where the15N enrichrnent of soil mineral N was simulated from the data for total N and labelled N accumulation taken from sequential harvests of either of the non-N2 -fixing control crops. This was then utilized in combination with the labelled N uptake data of the other crop to simulate its soil N uptake. However, the results using either technique indicated that the wheat and non-nod or nodulating beans exploited pools of N in the soil with completely different15N enrichments probably due to differences in exploitation of the soil N with depth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00748587
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  • 4
    Electronic Resource
    Electronic Resource
    Alternatives for nitrogen nutrition of crops in tropical agriculture (1995)
    Springer
    Nutrient cycling in agroecosystems 42 (1995), S. 339-346 
    Details
    ISSN: 1573-0867
    Keywords: Biofuel production ; biological nitrogen fixation ; french bean ; green manures ; soil organic matter ; soybean ; sustainable crop production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The development of sustainable agricultural systems for the tropics requires among other technologies, alternatives for nitrogen fertilizers which are often limited in availability for financial reasons and also represent a major source of groundwater and air pollution. There are many new alternatives for the development of agricultural systems which make use of biological processes in soil. Biological nitrogen fixation (BNF), that is, the biological conversion of atmospheric dinitrogen into mineral N, is the most important alternative among them. Examples are given of the impact of various technologies used in Brazil. Soybean, introduced into the country 30 years ago, is now the second most important export crop, reaching 24 million tons annually with no N fertilizer application. Consequently, Brazil today is the country in the world which uses the lowest amounts of nitrogen fertilizers in relation to phosphate. Alternatives for crop rotations and pastures are also discussed. Possibilities of expanding BNF to cereals and other non-legume crops are gaining new credibility due to the identification of endophytic associations with diazotropic bacteria. The definite proof of substantial BNF in sugar cane with N balance and15N methods in certain genotypes selected under low N fertilizer applications opens up new alternatives for sustainable agriculture and will be the key to viable bio-fuel programmes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00750526
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  • 5
    Electronic Resource
    Electronic Resource
    Use of the 15N natural abundance technique to quantify biological nitrogen fixation by woody perennials (2000)
    Springer
    Nutrient cycling in agroecosystems 57 (2000), S. 235-270 
    Details
    ISSN: 1573-0867
    Keywords: agroforestry ; forestry ; N2-fixation ; 15N natural abundance ; shrubs ; trees
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Biological nitrogen fixation (BNF) associated with trees and shrubs plays a major role in the functioning of many ecosystems, from natural woodlands to plantations and agroforestry systems, but it is surprisingly difficult to quantify the amounts of N2 fixed. Some of the problems involved in measuring N2 fixation by woody perennials include: (a) diversity in occurrence, and large plant-to-plant variation in growth and nodulation status of N2-fixing species, especially in natural ecosystems; (b) long-term, perennial nature of growth and the seasonal or year-to-year changes in patterns of N assimilation; and (c) logistical limitations of working with mature trees which are generally impossible to harvest in their entirety. The methodology which holds most promise to quantify the contributions of N2 fixation to trees is the so-called `15N natural abundance' technique which exploits naturally occurring differences in 15N composition between plant-available N sources in the soil and that of atmospheric N2. In this review we discuss probable explanations for the origin of the small differences in 15N abundance found in different N pools in both natural and man-made ecosystems and utilise previously published information and unpublished data to examine the potential advantages and limitations inherent in the application of the technique to study N2 fixation by woody perennials. Calculation of the proportion of the plant N derived from atmospheric N2 (%Ndfa) using the natural abundance procedure requires that both the 15N natural abundance of the N derived from BNF and that derived from the soil by the target N2-fixing species be determined. It is then assumed that the 15N abundance of the N2-fixing species reflects the relative contributions of the N derived from these two sources. The 15N abundance of the N derived from BNF (B) can vary with micro-symbiont, plant species/provenance and growth stage, all of which create considerable difficulties for its precise evaluation. If the%Ndfa is large and the 15N abundance of the N acquired from other sources is not several δ15N units higher or lower than B, then this can be a major source of error. Further difficulties can arise in determining the 15N abundance of the N derived from soil (and plant litter, etc.) by the target plant as it is usually impossible to predict which, if any, non-N2-fixing reference species will obtain N from the same N sources in the same proportions with the same temporal and spatial patterns as the N2-fixing perennial. The compromise solution is to evaluate the 15N abundance of a diverse range of neighbouring non-N2-fixing plants and to compare these values with that of the N2-fixing species and the estimate of B. Only then can it be determined whether the contribution of BNF to the target species can be quantified with any degree of confidence. This review of the literature suggests that while the natural abundance technique appears to provide quantitative measures of BNF in tree plantation and agroforestry systems, particular difficulties may arise which can often limit its application in natural ecosystems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009890514844
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  • 6
    Electronic Resource
    Electronic Resource
    Nitrogen fixation associated with grasses and cereals: Recent progress and perspectives for the future (1995)
    Springer
    Nutrient cycling in agroecosystems 42 (1995), S. 241-250 
    Details
    ISSN: 1573-0867
    Keywords: Acetobacter diazotrophicus ; Azospirillum spp. ; cereals ; grasses ; Herbaspirillum spp. ; nitrogen fixation ; sugar cane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Over the last 20 years many new species of N2-fixing bacteria have been discovered in association with grasses, cereals and other non-nodulating crops. Virtually all of these bacteria are microaerophylic, fixing N2 only in the presence of low partial pressures of oxygen. Until a few years ago much attention was focussed on members the genusAzospirillum and it was assumed that N2 fixation was restricted to the rhizosphere or rhizoplane of the host plants. Through the use of N balance and15N techniques it has been shown that in the case of lowland rice, several tropical pasture grasses and especially sugar cane, the contributions of biological N2 fixation (BNF) are of agronomic significance. More detailed study of the N2-fixing bacteria associated with sugar cane (Acetobacter diazotrophicus andHerbaspirillum spp.) has shown that they occur in high numbers not only in roots of this crop but also in the stems, leaves and trash but are rarely found in the soil. Some of these endophytic diazotrophs have now also been found in forage grasses, cereals, sweet potato and cassava, although evidence of significant BNF contributions is still lacking. The identification of these endophytic diazotrophs as the organisms probably responsible for the high contributions of N2 fixation observed in sugar cane suggests that it may be possible to attain significant BNF contributions in some other gramineae and perhaps root crops.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00750518
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  • 7
    Electronic Resource
    Electronic Resource
    Biological nitrogen fixation by two tropical forage legumes assessed from the relative ureide abundance of stem solutes: 15N calibration of the technique in sand culture (2000)
    Springer
    Nutrient cycling in agroecosystems 56 (2000), S. 165-176 
    Details
    ISSN: 1573-0867
    Keywords: Centrosema ; Desmodium ovalifolium ; 15N dilution technique ; N2 fixation ; Ureide technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The use of the relative ureide abundance (RUA) in the sap of mainly tropical ureide-producing legumes as a means to estimate the contribution of biological nitrogen fixation (BNF) is potentially an useful technique as it does not require the use of reference plants or additions of 15N-labelled fertilizer, and the analyses necessitate only relatively simple equipment. However, one problem in the application of the technique arises from the difficulty of obtaining sap samples from such legumes, especially small-stemmed forage legumes under field conditions. This study was conducted to investigate the possibility of using RUA in hot-water extracts of the stems of two forage legumes, Desmodium ovalifolium and a Centrosema hybrid, to estimate the contribution of BNF. In this case only ureide and nitrate are analysed to calculate RUA (100 × ureide-N/(ureide-N + nitrate-N)). The technique was calibrated with the 15N isotope dilution technique in sand culture where the plants were fed with 5 different levels of nitrate (0, 12.5, 25, 50 and 100 mg N pot-1). Despite the fact that in many stem extracts more than 90% of the N was neither nitrate or ureide, the colorimetric techniques utilised proved reliable and relatively immune to interference from other solutes in the extracts. One problem with the use of the 15N dilution technique to calibrate the RUA technique is that the former gives an integrated estimate of the BNF contribution since planting (or between harvests) and the latter is a point estimate at the time of sampling. This was overcome by using a `plant to plant simulation technique' where estimates of BNF are calculated from the daily accumulation of total N and the labelled N derived from the growth medium by the legumes using a curve-fitting strategy. These estimates of BNF for the days when stem extracts were analysed for nitrate and ureide showed linear correlations (r 2 = 0.82 and 0.90 for the D. ovalifoliumand Centrosema hybrid, respectively). This indicated that RUA of stem extracts of these two legumes was a reliable indicator of the BNF contribution, at least under controlled conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009865816182
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  • 8
    Electronic Resource
    Electronic Resource
    Estimation of N2 fixation in Desmodium ovalifolium from the relative ureide abundance of stem solutes: Comparison with the 15N-dilution and an in situ soil core technique (2000)
    Springer
    Nutrient cycling in agroecosystems 56 (2000), S. 177-193 
    Details
    ISSN: 1573-0867
    Keywords: 15N dilution technique ; Desmodium ovalifolium ; in situ N mineralisation ; N2 fixation ; ureide technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Many, but not all, legumes of tropical origin, transport fixed N from the nodules to the shoot tissue in the form of ureides, and the mineral N absorbed from the soil is principally transported in the form of nitrate. The analysis of stem xylem sap, or hot-water extracts of stem tissue, for ureide and nitrate has been used successfully to quantify BNF contributions to several grain legumes and more recently to some shrub and forage legumes. The objective of this study was to investigate the application of this technique to the quantification of the contribution of BNF to the forage legume Desmodium ovalifolium by comparing the relative ureide abundance (RUA) of stem extracts of this plant with simultaneous estimates of BNF obtained using the 15N isotope dilution technique. The first experiment was performed in pots of soil, taken from a grazing study, amended with 15N-labelled organic matter at four different application rates. The ureide concentration in the stem extracts reflected the changes in BNF activity during plant growth and the RUA was closely correlated with the proportion of N derived from BNF as determined from the 15N technique (r 2 = 0.86 and 0.88 for inoculated and non-inoculated plants, respectively). The use of a calibration curve derived from a previous study where the same legume was fed increasing concentrations of 15N labelled nitrate in sand/vermiculite culture, resulted in an over-estimation of the BNF contribution which may have been due to a significant uptake of ammonium from this acidic soil. The second experiment was performed in field plots and a good agreement was found between the estimates of BNF derived from using the ureide and 15N dilution techniques at two harvests six months apart. The uptake of soil N by the D. ovalifoliumand two forage grasses (Brachiaria humidicola and Panicum maximum) was estimated using an in situ soil core technique, and, while the uptake of N by the grasses was successfully estimated, this technique underestimated the N derived from the soil by the legume as determined by the ureide and 15N dilution techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009831705819
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  • 9
    Electronic Resource
    Electronic Resource
    Acetylene reduction in the rhizosphere of rice: Methods of assay (1978)
    Springer
    Plant and soil 50 (1978), S. 567-574 
    Details
    ISSN: 1573-5036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A method is described for thein situ assay of acetylene reduction activity in the rhizosphere of rice involving the use of inexpensive, lightweight equipment. The assay is quick to set up and thus many replicates can be run simultaneously. Control of any acetylene-reducing blue-green algae in the assay chamber is achieved with a photosynthetically active herbicide which has no measurable effect on rhizosphere activity. Results using this method are compared with those from an excised root assay of the same plants. Only a very weak correlation between the two methods was found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02107209
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  • 10
    Electronic Resource
    Electronic Resource
    Calculations and assumptions involved in the use of the ‘A-value’ and 15N isotope dilution techniques for the estimation of the contribution of plant-associated biological N2 fixation (1992)
    Springer
    Plant and soil 145 (1992), S. 151-155 
    Details
    ISSN: 1573-5036
    Keywords: N fertilizer ; nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In a paper published recently in this Journal a new equation was presented for the calculation of the proportion of plant nitrogen derived from plant-associated biological nitrogen fixation (BNF) using the ‘A-value’ technique. To apply this technique it is assumed that the specific availability (‘A-value’) of soil N is constant regardless of the quantity of added labelled N fertilizer. The authors stated that it follows from this assumption that the proportion of plant N derived from the 15N-labelled fertilizer (%Ndff) is proportional to the rate of addition of the labelled fertilizer. In this present paper we show that this is not the case, and furthermore data in the literature indicate that the ‘A-value’ of soil N is often not constant at different applied N levels. This technique, in common with the isotope dilution (ID) technique, relies on the assumption that the specific availability of soil N is equal for different plants (both ‘N2-fixing’ and ‘non-N2-fixing’). However, as in addition the assumption is made that the ‘A-value’ of soil N is constant at different rates of applied N, we argue that the ID technique is more reliable, particularly when BNF contributions are small.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00009551
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