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Fate of Azolla spp. and urea nitrogen applied to wetland rice (Oryza sativa L.) (1989)

Watanabe, I. ; Ventura, W. ; Mascariña, G. ; [et al.]

Springer

Biology and fertility of soils 8 (1989), S. 102-110

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ISSN: 1432-0789

Keywords: Azolla microphylla ; N cycling ; 15N method ; Wetland rice ; Anabaena azollae

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Summary Using 15N, the fate of N applied to wetland rice either as Azolla or urea was studied in a field at the International Rice Research Institute (IRRI). In bigger plots nearby, yield response and N uptake were also determined with unlabelled N sources. Azolla microphylla was labelled by repeated application of labelled ammonium sulfate. Labelled and unlabelled N were used alternately in applications of Azolla or urea 0 and 42 days after transplanting, in order to determine the effect of the time of application on the availability of Azolla N. The quantities of Azolla N incorporated were 23% more than those of urea N (30 kg N ha−1) in the isotope plots or 7% less in the yield response plots. Grain yield and total N uptake by the rice plants in the yield-response plots were higher in the urea-treated plots than in the Azolla-treated plots, but the physiological effect of Azolla N (grain yield response/increase in N uptake) was higher than that of rea. The labelled N balance was studied after the first and second crops of rice. Losses of labelled N after the first crop were higher from urea (30%–32%) than from Azolla (0%–11 %). Losses in N applied as a side dressing 42 days after transplanting were less than those of N applied basally. No further losses of 15N occurred after the first crop. The recovery of Azolla 15N in the first crop of rice was 39% from the basal application and 63% from the side dressing. The recovery of urea 15N was 27% from the basal application and 48% from the side dressing. Recoveries of residual N from both Azolla and urea during the second rice crop were similar. Laboratory incubation of the Azolla used and the changes in labelled exchangeable N in the soil showed that at least 65% of Azolla N (4.7% N content) was mineralized within 10 days.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00257752

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2

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Evaluation of nitrogen fixation by different strains of theAzolla-Anabaena symbiosis in the presence of a high level of ammonium (1989)

Okoronkwo, N. ; Hovel, C. ; Eskew, D. L.

Springer

Biology and fertility of soils 7 (1989), S. 275-278

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ISSN: 1432-0789

Keywords: Ammonium assimilation ; Azolla spp. ; Dinitrogen fixation ; Productivity-N content ; N yield ; 15N dilution technique

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Summary The proportion of N derived from N2 fixation for 99 strains ofAzolla spp. (comprising all known species) in the presence of ammonium (40 mg/1) was assessed using a15N-dilution technique. The percentage of N derived from air varied from 29.5% to 79.9%. Although the N concentration ofAzolla spp. was not correlated with fertilizer N, it correlated fairly well with N2 fixation. Regression analysis suggests that the N yield ofAzolla spp. is more dependent on N2 fixation than on ammonium assimilation. The high correlation between N yield and isotopically determined, fixed N2 indicates that the N yield could be used as a parameter in the selection ofAzolla spp. strains that are capable of maintaining high N2 fixation in the presence of a high level of ammonium.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00709661

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3

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Evaluation of the availability ofAzolla-N and urea-N to rice using15N (1986)

Kumarasinghe, K. S. ; Zapata, F. ; Kovacs, G. ; [et al.]

Springer

Plant and soil 90 (1986), S. 293-299

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ISSN: 1573-5036

Keywords: Azolla caroliniana (Willd.) ; Isotope dilution ; Nitrogen fixation

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Summary The symbiotic association of the water fernAzolla with the blue-green algaAnabaena azollae can fix 30–60 kg N ha−1 per rice cropping season. The value of this fixed N for rice production, however, is only realized once the N is released from theAzolla biomass and taken up by the rice plants. The availability of N applied asAzolla or as urea was measured in field experiments by two15N methods. In the first,Azolla caroliniana (Willd.) was labelled with15N in nutrient solution and incorporated into the soil at a rate of 144 kg N ha−1. The recovery ofAzolla-N in the above ground parts of rice [Oryza sativa (L) cv. Nucleoryza] was found to be 32% vs. 26% for urea applied at a rate of 100 kg N/ha; there was no significant difference in recovery. In the second, 100 kg N/ha of15N-urea was applied separately or in combination with either 250 or 330 kg N ha−1 of unlabelledAzolla. At the higher rate, the recovery ofAzolla-N was significantly greater than that of urea. There was a significant interaction when both N sources were applied together, which resulted in a greater recovery of N from each source in comparison to that source applied separately. Increasing the combined urea andAzolla application rate from 350 kg N ha−1 to 430 kg N ha−1 increased the N yield but had no effect on the dry matter yield of rice plants. The additional N taken up at the higher level of N application accumulated to a greater extent in the straw compared to the panicles. Since no assumptions need to be made about the contribution of soil N in the method using15N-labelledAzolla, this method is preferable to the15N dilution technique for assessing the availability ofAzolla-N to rice. Pot trials usingAzolla stored at −20°C or following oven-drying showed that both treatments decreased the recovery of N by one third in comparison to freshAzolla.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02277404

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4

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Mineral N effects on cowpea and soybean crops in a Nigerian soil (1982)

Eaglesham, A. R. J. ; Ayanaba, A. ; Ranga Rao, V. ; [et al.]

Springer

Plant and soil 68 (1982), S. 183-192

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ISSN: 1573-5036

Keywords: ‘AN’-value ; Cowpea ; Difference method ; Fertilizer-N ; Glycine max ; Nitrogen-15 ; N-balance ; N2-fixation ; Soybean ; Vigna unguiculata

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Summary The amounts of N fixed in the field in Nigeria by four cowpea and two soybean cultivars were determined at different levels of available N by the difference and the ‘AN’-value methods using non-nodulating soybean, maize and celosia as non-fixing controls. No significant differences were found between the two methods or with different controls. Grain removal and return of residues to the soil were measured and net soil-N changes calculated. N-benefits accrued from two of the cowpea cultivars when grown at low mineral-N levels, but with higher mineral-N availability, no cultivar contributed N because of inhibition of nodulation and lowered N2-fixation. Although the soybeans fixed more N than the cowpeas they caused greater net N-depletions because they sequestered a greater fraction of N in the grain.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02373704

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5

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Studies on the availability of Azolla N and urea N for rice growth using 15N (1990)

Sisworo, E. L. ; Eskew, D. L. ; Sisworo, W. H. ; [et al.]

Springer

Plant and soil 128 (1990), S. 209-220

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ISSN: 1573-5036

Keywords: Azolla pinnata var. pinnata ; dry season ; 15N recovery ; residual effect ; rice ; succeeding crop ; wet season

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Field experiments (20 m2 plots) were conducted to compare Azolla and urea as N sources for rice (Oryza sativa L.) in both the wet and dry seasons. Parallel microplot (1 m2) experiments were conducted using 15N. A total of approximately 60 kg N ha-1 was applied as urea, Azolla, or urea plus Azolla. Urea or Azolla applied with equal applications of 30 kg N ha-1 at transplanting (T) and at maximum tillering (MT) were equally effective for increasing rice grain yields in both seasons. Urea at 30 kg N ha-1 at T and Azolla 30 kg N ha-1 at MT was also equally effective. Urea applied by the locally recommended best split (40 kg at T and 20 kg at MT) gave a higher yield in the wet season, but an equal yield in the dry season. The average yield increase was 23% in the wet season, and 95% in the dry season. The proportion of the N taken up by the rice plants which was derived from urea (%NdfU) or Azolla (%NdfAz) was essentially identical for the treatments receiving the same N split. Recovery of 15N in the grain plus straw was also very similar. Positive yield responses to residual N were observed in the succeeding rice crop following both the wet and dry seasons, but the increases were not always statistically significant. Recovery of residual 15N ranged from 5.5 to 8.9% for both crops in succeeding seasons. Residual recovery from the urea applications was significantly higher than from Azolla in the crop succeeding the dry season crop. Azolla was equally effective as urea as an N source for rice production on a per kg N basis.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00011111

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6

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Mineral N effects on cowpea and soybean crops in a Nigerian soil (1982)

Eaglesham, A. R. J. ; Ayanaba, A. ; Ranga Rao, V. ; [et al.]

Springer

Plant and soil 68 (1982), S. 171-181

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ISSN: 1573-5036

Keywords: Acetylene reduction ; Cowpea ; Fertilizer-N ; Glycine max ; Nitrogen-15 ; Nodule ; Soybean ; Vigna unguiculata ; Yield

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Summary In a Nigerian soil depleted in available N, fertilizer-N enriched in15N was applied at 25 and 100 kg N/ha to crops of four cowpea and two soybean cultivars. Soil-N availability was estimated with three non-fixing crops, non-nodulating soybean, maize and celosia. With sequential harvests we examined the development of the fixing crops, as well as their nodulation profiles and acetylene reduction activities, and the patterns obtained were correlated with uptake of mineral-N. At low levels of mineral-N, excellent nodulation (up to 580 mg dry weight/plant) and very high acetylene reduction activities (up to 208 μmoles/plant/h) were recorded. Although fertilizer-N utilizations were low, 12% and 28% at 25 and 100 kg N/ha respectively, the lower application had a transient adverse effect on nodule development and the higher application had a long-term adverse effect on nodule formation, nodule development and acetylene reduction activity. Cowpea nodule mass reached maximum levels at early pod-fill except at 100 kg N/ha at which it continued to increase into late podfill. In contrast, soybean nodulation did not peak at any level of N but increased into late pod-fill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02373703

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7

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DNA amplification fingerprinting of the Azolla-Anabaena symbiosis (1993)

Eskew, D. L. ; Caetano-Anollés, G. ; Bassam, B. J. ; [et al.]

Springer

Plant molecular biology 21 (1993), S. 363-373

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ISSN: 1573-5028

Keywords: eukaryotic ; arbitrary oligonucleotide primer ; PCR ; prokaryotic ; silver staining ; taxonomy

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The Azolla-Anabaena symbiosis has been used for centuries as a nitrogen biofertilizer in rice paddies. Genetic improvement of the symbiosis has been limited by the difficulty in identifying Azolla-Anabaena accessions and Anabaena azollae strains. The recently developed technique of DNA amplification fingerprinting (DAF) was applied to this problem. DAF uses single, short, oligonucleotide primers of arbitrary sequence to direct amplification of a characteristic set of DNA products by a thermostable DNA polymerase in a thermocycling reaction. The products are separated in polyacrylamide gels and detected by silver staining. DAF could easily distinguish and positively identify accessions of Azolla-Anabaena with DNA extracted from the intact symbioses. The contribution of prokaryotic Anabaena sequences to the fingerprint of the intact symbioses, however, ranged from 0 to 77%, depending on the primer sequence. Therefore, DNA extracted from the intact symbioses would not be suitable for Azolla taxonomy studies. The fingerprints of Anabaena strains isolated by sucrose gradient centrifugation from different species of Azolla could be easily distinguished, and DAF patterns were used to confirm the maternal pattern of transmission of Anabaena in a sexual hybrid. Template DNA extracted from roots was used to produce fingerprints for Azolla without interference from the microsymbiont. Comparison of the patterns from the parents and a hybrid gave strong evidence confirming sexual hybridization.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00019951

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