Azolla and rice cultivation

The skill of Azolla’s symbiont, Anabaena, to sequester atmospheric nitrogen has been used for thousands of years in the Far East, where Azolla is extensively grown in rice paddies to increase rice production by way of more than 50%.

Rice is a vastly important staple in many tropical and temperate areas of the arena. Billions of folks depend on the crop to survive and hundreds of thousands at the moment are threatened by meals shortages which might be expanding each and every 12 months.

World rice production was approximately 645 million tonnes in 2007. At least 114 nations grow rice and greater than 50 have an annual manufacturing of 100,000 tonnes or extra. Asian farmers produce about 90% of the full, with two countries, China and India, growing more than half the total crop.

Nitrogen is the only maximum proscribing factor in rice cultivation, strongly affecting the crop yield. Azolla substantially will increase the volume of nitrogen fertilizer available to rising rice and it has been used for hundreds of years as a ‘green’ nitrogen fertilizer to increase rice manufacturing.

Research into Azolla’s use in rice production has subsequently grown during the last years, together with the advance of recent hybrids.

Azolla’s Build up in Rice Productivity:

Less than 5% of the nitrogen sequestered by means of Azolla is available immediately to the growing rice crops. The ultimate 95% stays in the Azolla’s biomass till the plant dies. As the plant decomposes, its organic nitrogen is hastily mineralized and launched as ammonia, which then becomes available as a biofertilizer for the rising rice crops.

Various ways have subsequently been advanced to maximize Azolla’s nitrogen fertilization, with the outcome that Azolla now has a monumental task to increase rice manufacturing worldwide and therefore alleviate meals shortages.

These come with learn how to building up the provision of the nitrogen assimilated through Azolla-Anabaena to the rising rice plants.

In Tanzania, Wagner (1996) carried out Azolla nilotica in various trials as an intercrop and bought increases of as much as 103% in rice grain yield.

Experiments at the University of California at Davis confirmed that Azolla larger rice yields via 112% over unfertilized controls when implemented as a monocrop right through the fallow season, by just 23% when applied as an intercrop with rice. However, the quantity higher via 216% when Azolla was implemented each as a monocrop and an intercrop (Peters, 1978).

Azolla’s Nitrogen Unlock into Water:

Most of the nitrogen fastened turns into available to rice handiest after the Azolla has decomposed, even supposing a small amount of ammonium is released into the water by Azolla right through expansion (Watanabe, 1984)

This was once confirmed by means of Chung-Chu (1984), who determined that most effective 3 to four% of the overall nitrogen fastened via Azolla is excreted into the water medium right through its expansion.

During decomposition, natural nitrogen is mineralized abruptly all the way through the first two weeks and then at an extra slow fee (Watanabe, 1984). Nitrogen is released mainly in the form of ammonium. Ammonium-nitrogen launched used to be discovered to stabilize at about 1 mg ammonium-N g-1 of fresh Azolla, which used to be 26-28% of the entire nitrogen content material of Azolla (Tung & Shen, 1985).

Azolla’s Incorporation of Nitrogen into Soil:

Incorporation of Azolla into the soil improves the release of nitrogen (Tung & Shen, 1985). If Azolla is grown as a monocrop and the sector will have to be drained a number of days upfront of incorporation. The remaining mat will have to be incorporated and the field stored tired for four or five days earlier than transplanting rice so as to pace decomposition (Lumpkin, 1987a).

Azolla’s Use as an Intercrop:

Azolla integrated 78 days after transplanting rice was once proven to contribute a better quantity of nitrogen to rice grain than used to be contributed by way of earlier incorporation (30-53 days after transplanting) (Ito & Watanabe, 1985). Since it has been discovered that the optimum stocking density for Azolla, with recognize to area-specific nitrogenase process, is roughly 50 to 100 g dry weight m-2 (Hechler & Dawson, 1995), nitrogen inputs may be very best maximized by means of widespread but partial incorporations of Azolla.

Other Advantages of Incorporating Azolla in Rice Cultivation:

As smartly as its nitrogen biofertilization, Azolla provides quite a lot of advantages for rice production and grows in a way this is complementary to rice cultivation:

The thick Azolla mat in rice fields suppresses weeds.

Since Azolla floats at the water floor, it does compete with rice for gentle and house.

In most climates, Azolla grows best under a partial shade of vegetation which is supplied by the rice canopy during early and intermediate phases of growth

When the rice approaches adulthood, Azolla begins to die and decompose because of low mild intensities underneath the cover and a depletion of vitamins, thus freeing its nutrients into the water.

Because Azolla decomposes rapidly, its nitrogen, phosphorus and different nutrients are hastily launched into the water and made available for uptake through rice all over grain development.

Azolla has a better talent than rice to acquire potassium in its tissues in low-potassium environments, offering rice with potassium after Azolla’s decomposition

In contrast with chemical nitrogenous fertilizers, Azolla has more than a few certain long-term effects, together with the improvement of soil fertility by increasing overall nitrogen, natural carbon, plus phosphorus, potassium, different nutrients and natural topic.

If chemical nitrogenous fertilizers are applied, the presence of an Azolla mat reduces ammonia volatilization that might normally occur.

When grown in a rice field, Azolla reduces the ammonia volatilization that happens following the appliance of inorganic nitrogen fertilizers by 20% to 50%. This is because of the truth that the Azolla duvet reduces mild penetration into the floodwater, thus hindering the rise of pH which in most cases stimulates ammonia volatilization in an Azolla-free rice box (Watanabe & Liu, 1992).