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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 174 (1995), S. 83-101 
    ISSN: 1573-5036
    Keywords: management ; legumes ; rhizobia ; symbiotic N2 fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Atmospheric N2 fixed symbiotically by associations between Rhizobium spp. and legumes represents a renewable source of N for agriculture. Contribution of legume N2 fixation to the N-economy of any ecosystem is mediated by: (i) legume reliance upon N2 fixation for growth, and (ii) the total amount of legume-N accumulated. Strategies that change the numbers of effective rhizobia present in soil, reduce the inhibitory effects of soil nitrate, or influence legume biomass all have potential to alter net inputs of fixed N. A range of management options can be applied to legumes growing in farming systems to manipulate N2 fixation and improve the N benefits to agriculture and agroforestry.
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  • 2
    ISSN: 1573-5036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Five Rhizobium strains were tested in the field with six Trifolium hosts. In order to examine criteria of evaluation of effectiveness under a range of sowing methods, all inoculant strains, plus controls, were sown with the six hosts in swards, with three of the hosts in rows and the other three as spaced plants. Swards and rows were assessed in terms of percentage plants nodulated, dry matter yield per unit area, visual rating of yield and mean dry weight of individually collected plants. Spaced plants were examined using the same criteria except that visual rating was replaced by area measurement. Harvested dry matter yield per unit area was accepted as the most reliable estimate for each of the sowing methods and served as a basis for comparison of other criteria. Percentage nodulation was generally not related to dry matter production in rows or swards, partly because of cross-infection between plants. Although the relationship was not good with spaced plants it was concluded that the prevention of root contact provided the only opportunity for a reliable measurement of the proportion of plants nodulated. Mean weights of individual plants removed from swards or rows did not provide a useful basis for strain comparison. The coefficients of variation of these plants commonly exceeded 100%. Although a calculated yield (mean plant weight × no. of plants) ranked strains similarly to the full harvest, the time and labour requirement was higher. Visual rating of yield was most reliable with rows where the observer could successfully scan all treatments. It was less reliable with swards. Area measurement of spaced plants was not related to yield. In spite of some anomalies between swards and rows, there was generally good agreement in ranking of strains in terms of harvested yield between all sowing methods. re]19730821
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  • 3
    ISSN: 1573-5060
    Keywords: N2 fixation ; breeding ; food legumes ; measurement techniques ; nodulation ; nitrate tolerance ; yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Dinitrogen fixation and legume productivity are greatly influenced through the interactions of legume host, Rhizobium, and the above- and below-ground environment. The benefits of improving legume N2 fixation include reduced reliance on soil N, leading to more sustainable agricultural systems and reduced requirements for fertilizer N, enhanced residual benefits to subsequent crops, and increased legume crop yields. Most of the gains in N2 fixation to date have been derived from management of legume cropping systems and through inoculation of legume seed with competitive and symbiotically effective rhizobia. Further gains are possible by developing plant cultivars with tolerance to soil abiotic factors, increased plant yield, and a broader and more effective matching of plant host and rhizobia. Techniques for screening material for superior N2 fixation and examples of programs to increase fixed N, with attention to the major abiotic stresses, are discussed.
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  • 4
    ISSN: 1573-5036
    Keywords: field ; Korean genotypes ; nitrate tolerance ; N2 fixation ; nodulation ; soil nitrate ; soybean ; ureides ; xylem exudate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The development of cultivars of soybean (Glycine max L. Merr.) which are capable of near-maximum levels of N2 fixation in high-NO 3 − soils remains a high priority in N2 fixation research. We report a field study to evaluate nodulation and N2 fixation by 32 genotypes of soybean, selected after two years of glasshouse screening for superior symbiotic activity in the presence of 2.5 mM NO 3 − . The 32 “NO 3 − -tolerant” genotypes and eight others (three commercial “check” cultivars and five “non-fixing” lines) were inoculated withBradyrhizobium japonicum CB 1809 and sown into a black earth soil (fine, montmorillonitic, thermic Udic Pellusterts) which contained high levels of soil NO 3 − (260 kg N ha−1; 0 to 120 cm depth) and which was free of soybean rhizobia. Nitrogen fixation activity was assessed at 89 days after sowing using the relative abundance of ureides in xylem exudate [(ureide-N/ureide-N+NO 3 − -N+α amino-N)×100] as an index of fixation. Plant growth and nodulation were assessed 11 days later. Genotypes 466, 468, 469 and 464, all of Korean origin, showed the highest levels of symbiotic activity. Many of the remaining 28 “tolerant” genotypes nodulated poorly in the field and displayed levels of N2 fixation (relative ureides) which were equivalent to two of the commercial “check” cultivars, Bragg and Elf. Correlation matrices of the measured parameters revealed highly significant correlations among the indices of nodulation and N2 fixation and poor correlation between those measurements and plant growth-seed yield. The levels of NO 3 − tolerance, displayed by the four Korean lines, may prove useful in breeding programs which aim to enhance N2 fixation by soybean in high-NO 3 − soils.
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  • 5
    ISSN: 1573-5036
    Keywords: intercropping ; N2 fixation ; natural15N abundance ; ureides ; Vigna umbellata ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The yield of N in maize (Zea mays L.) and ricebean (Vigna umbellata [Thumb.] Ohwi and Ohashi) were compared on a Tropoqualf soil in North Thailand in 1984 and 1985. Both species were grown in field plots in monoculture or as intercrops at a constant planting density equivalent to 8 maize or 16 ricebean plants per m2. The contribution of symbiotic N2 fixation to ricebean growth was estimated from measurements of the natural abundance of15N (δ15N) in shoot nitrogen and from analysis of ureides in xylem sap vacuumextracted from detached stems. The natural abundance of15N in the intercropped ricebean was found to be considerably less than that in monoculture in both growing seasons. Using maize and a weed (Ageratum conyzoides L.) as non-fixing15N reference plants the proportions (P 15N) of ricebean shoot N derived from N2 fixation ranged from 0.27 to 0.36 in monoculture ricebean up to 0.86 when grown in a 75% maize: 25% ricebean intercrop. When glasshouse-derived calibration curves were used to calculate plant proportional N2 fixation (Pur) from the relative ureide contents of field collected xylem exudates, the contribution of N2 fixation to ricebean N yields throughout the 1985 growing season were greater in intercrop than in monocrop even at the lowest maize:legume ratio (25∶75). Seasonal patterns of sap ureide abundance indicated that N2 fixation was greatest at the time of ricebean podset. The averagePur andP 15N in ricebean during the first 90 days of growth showed identical rankings of monocrop and intercrop treatments in terms of N2 fixation, although the two sets ofP values were different. Nonetheless, seasonal estimates of N2 fixation during the entire 147 days of legume growth determined from ureide analyses indicated that equivalent amounts of N could be fixed by ricebean in a 75∶25 intercrop and in monoculture despite the former being planted at one-quarter the density.
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  • 6
    ISSN: 1573-5036
    Keywords: legumes ; N2 fixation ; 15N analysis ; ureides ; xylem exudate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Methods for partitioning the nitrogen assimilated by nodulated legumes, between nitrogen derived from soil sources and from N2 fixation, are described as applied in peninsular Malaysia. The analysis of nitrogenous components translocated from the roots to the shoots of nodulated plants in the xylem sap is outlined, with some precautions to be observed for applications in the tropics. Some examples of the use of the technique in surverying apparent N2 fixation by tropical legumes, in studying interrow cropping in plantation systems and in assessing effects of experimental treatments on N2 fixation by food legumes, are described. Techniques for assesing N2 fixation by means of15N abundance have been used to show that applications of nitrogenous fertilizers commonly used in Malaysia for soybeans depress N2 fixation, that similar results are obtained with natural abundance and15N-enrichment methods and that, in at least two locations in Malaysia, differences between the natural abundance of15N in plant-available soil nitrogen and in atmospheric N2 are great enough to permit application to measurement of N2 fixation by leguminous crops.
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  • 7
    ISSN: 1573-5036
    Keywords: Azolla ; Casuarina ; legume ; nitrogen fertilizer ; rhizobia ; symbiotic N2 fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A fundamental shift has taken place in agricultural research and world food production. In the past, the principal driving force was to increase the yield potential of food crops and to maximize productivity. Today, the drive for productivity is increasingly combined with a desire for sustainability. For farming systems to remain productive, and to be sustainable in the long-term, it will be necessary to replenish the reserves of nutrients which are removed or lost from the soil. In the case of nitrogen (N), inputs into agricultural systems may be in the form of N-fertilizer, or be derived from atmospheric N2 via biological N2 fixation (BNF). Although BNF has long been a component of many farming systems throughout the world, its importance as a primary source of N for agriculture has diminished in recent decades as increasing amounts of fertilizer-N are used for the production of food and cash crops. However, international emphasis on environmentally sustainable development with the use of renewable resources is likely to focus attention on the potential role of BNF in supplying N for agriculture. This paper documents inputs of N via symbiotic N2 fixation measured in experimental plots and in farmers' fields in tropical and temperate regions. It considers contributions of fixed N from legumes (crop, pasture, green manures and trees), Casuarina, and Azolla, and compares the relative utilization of N derived from these sources with fertilizer N.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 174 (1995), S. 51-82 
    ISSN: 1573-5036
    Keywords: breeding ; crop legume ; heritability ; nitrate tolerance ; nodulation ; N2 fixation ; rhizobia ; yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Legume N2 fixation is variable, but nonetheless is a valuable process in world agriculture. There is great potential to increase the contribution by the crop legumes to the world's supply of soil.N. This will be achieved by (i) increasing the area of legumes sown by farmers; (ii) improved management of the crops in order that the major determinants of productivity, e.g. land area, water availability, are converted to harvested product with maximum efficiency; and (iii) genetic modification of the commonly-grown species to ensure high dependence of the legume crop on N2 fixation at all levels of productivity. Currently-used methods for measuring N2 fixation and for assessing heritability and repeatability of N2 fixation in breeding and selection programs are reviewed. Results from research programs to define genetic variation in N2 fixation and to enhance N2 fixation through selection and breeding are presented with particular emphasis on common bean (Phaseolus vulgaris) and soybean (Glycine max).
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 40 (1974), S. 441-444 
    ISSN: 1573-5036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Pelleting inoculated seed of Vigna sinensis, Glycine wightii cv. Clarence, Lupinus albus, Desmodium uncinatum cv. Silverleaf and Glycine max with neutral rock phosphate rather than lime did not improve the survival of their non-acid producing rhizobia. The rhizobia survived equally well when applied in a 15% w/v gum arabic slurry and not pelleted. re]19730706
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  • 10
    ISSN: 1573-5036
    Keywords: humid tropics ; N balance ; N2 fixation ; N fertilizer ; nodulation ; rice ; rotation ; soybean
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We report a study in northern Thailand to examine the effects of fertilizer N, applied both to paddy rice and to a subsequent soybean crop on symbiotic and yield characteristics of soybean and on the differences between inputs of fixed N2 and the removal of N as harvested product. Treatments were a factorial arrangement of 0, 100 and 300 kg N ha-1 applied to the rice (designated R0, R100 and R300, respectively), and 0,25 and 50 kg N ha-1, applied as ‘starter’ fertilizer to the soybean (S0, S25 and S50, respectively). Nitrogen applied to the rice increased rice yields by up to 74% but proportions recovered by the rice were low (45% [R100] and 14% [R300]). The rice N treatments had only marginal effects on soybean nodulation (up to 17% reduction in early growth) and above-ground dry matter (up to 9% increase). Effects on soybean seed yield and total N2 fixed were insignificant. Starter N, applied to the soybean at sowing, also marginally reduced nodulation and enhanced above-ground dry matter. Total N2 fixed was unaffected but seed yield was increased by up to 6%. For all treatments, total above-ground N ranged from 145 to 179 kg ha-1 with 72 to 85% (122 and 140 kg ha-1) derived from N2 fixation. When harvested product consisted of seed only, differences between inputs of fixed N2 and removals of seed N were close to zero (-10 to+9 kg N ha-1) with little effect of fertilizer N. The N balances were reduced by an average of 18 kg N ha-1 when straw was included as harvested product. We concluded that N applied to the rice and to the following soybean was inefficiently used by those crops and had only marginal effects of symbiotic activity of the soybean. Furthermore, the benefit of the N2 fixing soybean in this system was to slow the decline of, rather than enhance, the N fertility of the soil
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