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Azolla and Blue-green Algae as Alternative Sources of Nitrogen for Rice and Their Mineralization in Soils of Bangladesh

AMINUL ISLAM
Professor
University of Dhaka, Dhaka 2, Bangladesh

ABDUL LATIF MOLLA
Research Fellow
University of Dhaka, Dhaka 2, Bangladesh

SIRAJUL HOQUE
Lecturer
Department of Soil Science, University of Dhaka, Dhaka 2, Bangladesh

Abstract/ Executive Summary:

Application of Azolla @ 60 kg N/ha and a blue-green algae mixture of Nostoc and Anabaena @ 90 kg N/ha, either alone or in combination with urea, significantly increased the straw and grain yields and N content of straw and grain of 'BR3', rice (Oryza sativa Linn.). Azolla and blue-green algae were as effective as urea in encouraging vegetative growth and in increasing the assimilation of N by rice, Urea was completely mineralized within 7 days, while Azolla and blue-green algae released a significant amount of ammonium only after 7 days, with complete mineralization within 8 weeks. Any saving in the consumption of chemical nitrogen fertilizer without affecting the soil productivity will not only be an economic but also a strategic necessity (Venkataraman, 1977). Hence a study was conducted to find out the effect of Azolla and blue-green algae as alternative sources of nitrogen for 'BR3' rice (Oryza sativa Linn.) in Bangladesh.

Keywords: Azolla, Blue-green algae,Nitrogen, Mineralization, Rice

Location: Dhaka University

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Bio fertilizer

Objectives:

To find out the effect of Azolla and blue-green algae as alternative sources of nitrogen for 'BR3' rice (Oryza sativa Linn.) in Bangladesh.

Methodology:

Greenhouse experiments were conducted with Azolla (green Azolla with 4.2% N. C:N ratio 7.8, and red Azolla with 2.55% N, C:N ratio 15) and a blue-green algae mixture of Nostoc and Anabaena spp (with 3.81%N, C:N ratio 7.3) to investigate their effects on rice Naraibag silty loam (pH 6.7, C:N ratio 9 and total N 015% and Kalma silty clay (pH 7.7, C:N ratio 9 and total N 0.08%) were used for the experiment with Azolla and only Naraibag silty loam was used for the experiment with blue-green algae. The treatments consisted of 30 and 60 kg N/ha from dried Azolla, urea and Azolla + urea in the Azolla experiment, and 60 and 90 kg N/ha from dried blue-green algae, urea and blue –green algae + urea in the blue-green algae experiment. There were 18 treatments (11 for Azolla and 7 for blue-green algae experiments) including the control (no fertilizer) replicated thrice in a completely randomized design. In the Azolla experiment 5-week-old seedlings were planted 1 seedling/pot, and in the blue-green algae experiment 4-week-old seedlings were planted 1 seedling/hill and 3 hills/pot. The water level in each pot was maintained to a depth of 2-3 cm until the grain matured. Plant samples were collected at maximum tillering and harvesting stages of rice in the Azolla experiment, and at tillering, flowering and harvesting stages of rice in the blue-green algae experiment. After harvest, the dry weights of straw and grain were recorded, and the grains were analysed for total N by the Kjeldahl rnethod (Jackson, 1958). A separate laboratory incubation experiment (at 30⁰C ± l⁰C) was conducted to study the release of available N (NH₄N and NO₃N) from Azolla and bluegreen algae, the soil and treatments being the same. The ammonia released at 1,2,4 and 8 weeks of incubation was measured (Bremner and Shaw, 1955).

Source of Information: Indian J. agric. Sci. 54 (12): 1056-61,December 1984

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Application of Azolla @ 60 kg N/ha either alone or in combination with urea significantly increased the tiller number of rice in both the soils but did not affect plant height. Blue-green algae applied @ 90 kg N/ha increased the plant height and blue-green algae + urea applied @ 90 kg N/ha increased the tiller number significantly at both stages of growth. Azolla @ 6o kg N/ha either alone or in combination with urea significantly increased the straw and grain yields, which were not significantly different from the yield obtained with urea alone @ 90 kg /ha ( except straw yield from Azolla in Naraibag soil). Application of blue-green algae @ 90 kg N/ha significantly increased the straw and grain yields and blue-green algae + urea applied @ 90 kg N/ha gave the highest yield. A combination of urea with Azolla or blue-green algae enhanced the mineralization.ve the highest yield.

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