Azolla As An Alternative NITROGEN Source For Rice Crop Production

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Posted by: nantha, on 10/7/2007, in category "Organic cultivation Techniques for Various crops"
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Location: Thanjavur, Tamilnadu, India

Abstract: Azolla live in symbiosis with a Cyanobacteria which is able to fix N2-air.

Lowland rice is one of the main sources of the staple diet in the east, south,south-east Asia. The main constrain of this lowland is the soil fertility that is  unsustainable. This is very important due to the fact that currently and in the future the lowland rice production will have to be accelerated, to meet the needs of the growing population in this region. It is observed that at lowland soils, the soil organic matter (SOM) and the soil nitrogen content are limited if not in deficiency. One effort needed to meet this limitation is to apply chemical fertilizers especially Nfertilizer, at high rates. But the risk of using N-fertilizers at high rates is its low efficiency and the potential pollution of ground water caused by nitrate.

To solve this problem is to decrease the rates of the chemical fertilizers and to replace a part of the chemical fertilizers by an alternative N source. One of the alternatives N source is biofertilizers. One of the biofertilizers which have a great potential as a nitrogen source and to build SOM is green manure. From years of study done by BATAN, Azolla is a suitable green manure as an alternative nitrogen source and a source of organic matter.

Azolla is a water fern plant. What has been studied by BATAN is the mini Azolla with a size of 3 – 4 cm. Azolla live in symbiosis with a Cyanobacteria which is able to fix N2-air. The Cyanobacteria is Anabaena Azollae. This symbiosis makes Azolla to have a quite high N content. Azolla is indigenous in Asia, America, Europe and Africa. It has been widely used for centuries in China and Vietnam as nitrogen source for lowland rice.

Nutrients content of Azolla

It was found that Azolla, which symbiosis with Anabaena Azollae, could fix N2 at a rate of 70 – 90%. The N2-fix, which accumulated in the Azolla’s body, is used as altternative N-source for lowland rice.

Several studies showed that the growth rate of Azolla is 0.355 – 0.390 gram per day in the laboratorium and 0.144 – 0.860 gram per day in the field. Generally in the field Azolla reach maximum biomass after 14 –28 days after its inoculation. Studies done by BATAN showed 3–4 weeks after inoculation at rate of 200 g fresh Azolla per m2 the whole field at the water surface would be covered. When the whole field is covered by Azolla it could be expected that it could contribute 30 -45 kg N per ha or equal to 100 kg urea. It was found that Azolla grow better in the rainy season as long as water is available.

The benefit of Azolla

• Source of N which could replace urea up to 100 kg
• Feed for fish and small animals,especially chickens and ducks
• Suppress growth of weeds
• As an ornamental water plant
• Control of mosquitos
• After using of Azolla for four seasons or more in lowland rice it could replace P-fertilizer up to 50% from the usual rate applied.

Promising Technology
Azolla is one of green manure sources, because they are (1) easily mineralized (21 – 24 days after inoculation), (2) capable of supplying enough N needed by plants (30 kg N/ha) and (3) capable of reducing the loss of N from urea and (4) could be grown by farmers going to use it. Due to the high capability of Azolla to fix N2 in water, Azolla can be a promising source of green manure for wetland rice.