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Azolla: A potential bio-fertilizer for terrace rice cultivation

Dimapur (Agencies)
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Published on 27 Feb. 2013 1:04 AM IST
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Repeated cultivation of the same crop each year on the same piece of land robs soil of the essential nutrients leading to reduced and erratic yields.

Imtilemla, SMS (Soil Conservation), KVK, Tuensang stated that in the context of depleting soil fertility and high prices of chemical fertilizers/ no use of fertilizers, use of biofertilizer- a cheaper and renewable source of low cost plant nutrient is important for cultivators to combat the aforesaid problem.

For terraced rice cultivation, use of azolla fern is advocated which is a good organic fertilizer and can also limit problems of weeds and insect pest such as leaf rollers. Azolla is a fresh water fern which can be seen in many flooded rice fields.

But farmers fail to realize its importance in contributing soil fertility especially in nitrogen supply. It is associated with a blue-green algae that fixes nitrogen from the atmosphere.

As such it supplements nitrogen to rice crop for better crop growth, crop production and maintains soil fertility. It is known to contribute 40-60 kg N/ha (86-129 kg Urea) per rice crop.

Their nitrogen fixing ability has led to it being widely used as a biofertilizer, especially in parts of south east Asia.

Azolla is a genus of seven species of aquatic ferns, the only genus in the family Azollaceae. They are extremely reduced in form and specialized, looking nothing like conventional ferns.

Azolla caroliniana, native to the Americas, a cold tolerant species has shown good adaptability in diverse locations of Tuensang district.

It is reported to survive well even at very low winter temperature of 5° C during the months of December to February in mid hills of Meghalaya too.

Azolla floats on the surface of water by means of numerous, small, closely-overlapping scale-like leaves, with their roots hanging in the water.

It readily colonizes areas of fresh water, and grows at great speed-doubling its biomass every two to three days.

When it dies and decays in the soil, nitrogen becomes available to rice plant. It can be applied in two ways: green manure form- cultivated in special fields or ponds and latter added as compost to the rice or other crops and dual crop form-cultivation of azolla in rice field and incorporation into the paddy soil during intervals.

In rice fields it can be applied in both ways. But the application of green azolla form produces better result than dry form.

One week after transplanting rice seedlings fresh azolla @ 200-300 gms/sq.m can be applied in the standing crop.

Azolla biomass quickly multiplies in 3-4 weeks. Water is drained out from the field and the azolla is ploughed to mix with the soil.

This should be done at least twice during the cropping season. Hence the decomposition of azolla enriches soil organic matter and supplies nitrogen to rice plant and increases rice yield upto 20-30%.

Because of its high protein content azolla can be used for feeding milking cattle, pigs, ducks and chickens.

It has also been reported that their manure contains higher nutrients compared to those on regular diets. Besides, green azolla is also a good feed for fishes.

Since azolla decomposes easily within 7-10 days, it can be raised and multiplied by any ordinary farmer for making good quality compost.

For this, a pit size of 2m X 1m X 20cm lined with poly/silpaulin sheet is to be constructed, water level should be maintained at about 10 cm.

Then introduce 400 gm azolla/pit and since azolla is very responsive to Phosphorus, apply 10 gms SSP for rapid growth.

It should be harvested when it forms a dense mat on the water surface and kept in gunny bags to allow the water to drain.

 
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