Ebook: Isotopic Studies of Azolla and Nitrogen Fertilization of Rice: Report of an FAO/IAEA/SIDA Co-ordinated Research Programme on Isotopic Studies of Nitrogen Fixation and Nitrogen Cycling by Blue-Green Algae and Azolla

Nitrogen is the most limiting element for crop production. Traditionally, expensive commercial fertilizers are used to correct soil nitrogen deficiencies. Indeed, 50% of the increase in rice yields after World War II can be attributed to increased fertilizer nitrogen use. Although an increased rate of fertilizer nitrogen application has been advocated to meet the growing demand for food, it is unrealistic to advise the farmers to apply fertilizers they could hardly afford, and whose prices are likely to escalate in the years ahead. In addition, when they are not applied judiciously there are problems of environmental pollution as plants are capable of taking up only a relatively small portion of the applied nitrogen, a substantial amount being lost through various chemical and biological processes. The exploitation of cheaper alternatives or supplements to fertilizers have therefore gained much interest in recent years.
Our increased interest in biological nitrogen fixation as a supplement or alternative to nitrogen fertilizers led to the convening of a consultants' meeting on `The Role of Isotopes in Studies on Nitrogen Fixation and Nitrogen Cycling by Blue-Green Algae and the Azolla-Anabaena azollae Association', in Vienna from 11--15 October 1982. The consultants' group recommended that the Joint FAI/IAEA Division of Nuclear Techniques in Food and Agriculture embark on a coordinated research programme in this field and that initial emphasis should be placed on Azolla-Anabaena symbiosis. As a result, such a programme was initiated in 1984, which was concluded in 1989. The results and conclusions reported here are those that were generated during the five years of its operation.

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Content:
Front Matter....Pages i-xi
Introduction....Pages 1-2
Assessment of nitrogen fixation in Azolla using the 15N isotope dilution technique....Pages 3-15
Comparison of the direct and indirect 15N methods for evaluation of N uptake by rice from Azolla....Pages 16-22
Use of 15N labelled ammonium sulphate and 15N-labelled urea as a source for labelling Azolla with 15N....Pages 23-31
Effects of urea and Azolla on N uptake and yield of rice....Pages 32-41
Co-ordinated field evaluation of Azolla N uptake and yield response of rice in Bangladesh, China, Indonesia, Pakistan, The Philippines, Sri Lanka and Thailand....Pages 42-54
Residual effects of Azolla N to a second crop of rice or wheat....Pages 55-60
A comparative study of the effects of Azolla species and strain on availability of N to rice....Pages 61-65
Comparison of the availability of N from fresh vs dried Azolla ....Pages 66-70
Effects of phosphorus fertilization on growth and N accumulation in Azolla....Pages 71-78
Nitrogen balance studies in Azolla/rice cropping systems....Pages 79-86
Increasing fertilizer use efficiency of urea using Azolla ....Pages 87-97
Summary and conclusions....Pages 98-102
References....Pages 103-107
Back Matter....Pages 109-147

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Content:
Front Matter....Pages i-xi
Introduction....Pages 1-2
Assessment of nitrogen fixation in Azolla using the 15N isotope dilution technique....Pages 3-15
Comparison of the direct and indirect 15N methods for evaluation of N uptake by rice from Azolla....Pages 16-22
Use of 15N labelled ammonium sulphate and 15N-labelled urea as a source for labelling Azolla with 15N....Pages 23-31
Effects of urea and Azolla on N uptake and yield of rice....Pages 32-41
Co-ordinated field evaluation of Azolla N uptake and yield response of rice in Bangladesh, China, Indonesia, Pakistan, The Philippines, Sri Lanka and Thailand....Pages 42-54
Residual effects of Azolla N to a second crop of rice or wheat....Pages 55-60
A comparative study of the effects of Azolla species and strain on availability of N to rice....Pages 61-65
Comparison of the availability of N from fresh vs dried Azolla ....Pages 66-70
Effects of phosphorus fertilization on growth and N accumulation in Azolla....Pages 71-78
Nitrogen balance studies in Azolla/rice cropping systems....Pages 79-86
Increasing fertilizer use efficiency of urea using Azolla ....Pages 87-97
Summary and conclusions....Pages 98-102
References....Pages 103-107
Back Matter....Pages 109-147
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