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Azolla Benefits, Uses, Role, Importance in Rice Production

Azolla Benefits, Uses, Role, Importance in Rice Production

Azolla Benefits for Paddy Cultivation:

We know Azolla is a great feed for livestock such as poultry, pigs, dairy, fish, goat, and sheep. However, today, let us talk about Azolla Benefits and its role as biofertilizer in paddy cultivation which finally results in reduced cultivation cost of rice, and increased yield of paddy.

Introduction of Azolla in Paddy fields:

In recent years the use of biofertilizers in is gaining importance. In this aspect, attracted the attention of agricultural scientists. The importance of Azolla as organic manure in rice was first demonstrated in North Vietnam in the year 1957 and subsequently introduced in U.S.A, Indonesia, Japan, Philippines, China, and India. The potential of Azolla as a green manure crop for rice has since been stressed. Azolla is a genus of water fern that assimilates nitrogen in association with a nitrogen-fixing blue-green alga Anabaena Azolla that lives symbiotically in the cavities of the upper leaf lobes of Azolla.

Azolla can be grown abundantly in N-deficient medium also because of the infixing activity of the endo-cyanophyte Anabaena azollae. Biological nitrogen fixation through Azolla Anabaena complex is a potential biological system for increasing rice yields, at comparatively low cost. Azolla possesses the desired qualities of a green manure crop, like quick growth, large biomass production, higher nitrogen content and easy decomposability in the soil. It has been further demonstrated that Azolla is a good source of potassium when applied to soils.

However, Azolla cultivation is a labor-intensive technology and it is, therefore, suitable for adoption in locations where farm labor is affordable. The main constraints in the use of Azolla fertilization to rice are moisture, temperature stress, P status in the soil, salinity, pests, and diseases. Since water is a pre-requisite for the growth of Azolla, it can be grown in higher rainfall areas where water is adequate and as such, it is not suitable under dryland conditions.

Read Azolla Farming Project Report, Cost, profits.

Suitable climate to grow Azolla:

Azolla is reported to grow and multiply well from July to February in India but dies rapidly at higher temperature. In many agro-climatic regions of India, maintenance of Azolla is a serious problem because of high temperatures. Hence, it is necessary to screen and select a suitable Azolla strain which is temperature tolerant and adaptable to particular climatic condition. This is of the paramount importance of introducing Azolla bio-fertilizer technology in rice production. Under less favorable conditions, application of P fertilizer is necessary to produce Azolla biomass. If P deficient conditions occur, the growth of Azolla will stop. Since most of the rice soils are deficient in P, it is necessary to apply P for Azolla and is considered as a costly input. Thus, cheaper sources of supplying the required P have to be investigated. Salinity is a major problem confronting rice cultivation in several parts of India. Therefore, salt-tolerant Azolla species are to be identified, that can be used as green manure in saline soils.

Azolla Production.
Azolla Production.

The beneficial effect of Azolla as green manure has been well documented. There are only a limited number of studies on the decomposition and availability to rice of nitrogen fixed by Azolla. For the effective use of Azolla, it is important to study the fate of Azolla nitrogen and its availability to the rice plant. With the increasing cost of fertilizer, the cost of this input in rice cultivation is becoming prohibitive as fertilizers alone are reported to cost 40 to 50 percent of the total input. In order to decrease the cost of fertilizer, organic fertilizers like Azolla can be substituted for chemical fertilizers. Use of organic fertilizer mobilizes cheap resources for productive purpose replacing high-cost chemical fertilizers. Azolla, which has attracted the attention of biological 3 scientists, since the past three decades is considered to have a high potential for replacing inorganic N fertilizers because it can fix N from the atmosphere. Besides increasing the organic carbon content and N availability in soil, Azolla is a good source of other nutrients and possess the other agronomic qualities associated with the other green manure crops. The economic potential of Azolla is also reported to be considerable. The economic return due to the adoption of bio-fertilizer technology, in terms of saving on the cost of chemical fertilizer and weedicides is always more than 10 percent provided the environmental conditions for growth and multiplication of Azolla are properly met.

Therefore, once Azolla is introduced into a rice field, it can sustain and act as a renewable biofertilizer. Principally there are two methods of using Azolla, as dual cropping and growing in the nursery and using prior to transplanting. An increase in paddy yields, due to inoculation of Azolla has been reported by several investigators in India and abroad

How Does it work: 

Azolla is a genus of fresh small aquatic ferns that are native to Asia, Africa, and the Americas, Three Azolla species are native to parts of the United States, They live naturally in lakes, swamps, streams, and other bodies of water, Some have been spread by man or natural means to various parts of the world. Some are strictly tropical or subtropical in nature, while others grow and thrive in either temperate or tropical climates. Azolla has been of interest to botanists and agriculturists for years because of its symbiotic relationship with a nitrogen-fixing, blue-green alga, Anabaena

What Are the Benefits of Using Azolla?

Azolla as a Nitrogen Fertilizer for increasing Crop Yields: Azolla plants are described by the Chinese and Vietnamese as being miniature nitrogen fertilizer factories. The Vietnamese use them as nitrogen fertilizer since Azolla continued to produce nitrogen fertilizer for Vietnamese rice paddies. The nitrogen fertilizer fixed by Azolla becomes available to the rice after the Azolla mat is incorporated into the soil and its nitrogen begins to be released through decomposition. For Azolla, it takes 25 to 35 days to provide enough nitrogen for a 4 to 6 ton/ha rice crop during the rainy season, or a 5 to 8 ton/ha crop under irrigation during the dry season.

Maintaining Soil Fertility: As a green manure, Azolla’s influence on soil fertility is due to its organic matter and nitrogen. Incorporation and decomposition of Azolla will form a humus compound. Humus increases the water holding capacity of soil and promotes aeration, drainage, and the aggregation essential for highly productive soils, Organic matter can bind together soil particles and makes clayey soils more friable. Apart from its influence on soil physical properties, Azolla is important in the cycling of nutrients, while Azolla is growing in the paddy, it fixes nitrogen and absorbs nutrients out of the water that might otherwise be washed away. When the Azolla is composed with the soil and humus is formed, and these nutrients are slowly released into the soil as decomposition progresses.

Controlling the Growth of Aquatic Weeds: Agricultural economists have calculated that the Asian farmers, particularly women, pay longer time on weeding than on any other activity required for rice production. Although research is insufficient, it is commonly believed that Azolla suppresses the growth of certain aquatic weeds. Weed growth is suppressed once Azolla forms a thick, light-proof mat. There are mainly two mechanisms for this suppression, the most effective mechanism is the light-starvation of young weed seedlings by the blockage of sunlight. And the other is the physical resistance to weed seedling is exposed in a heavy, interlocking Azolla mat. In the case of weed-infested rice fields, the benefit from Azolla weed suppression may even surpass its benefit as a nitrogen source. Rice seedlings are not affected by Azolla’s weed suppression effect because, when transplanted, they stand above the Azolla mat.

Read: Kitchen Garden Tips, Ideas, Benefits, Design.

How Azolla Is Used as a Green Manure: Azolla can be used as a green manure by growing it as a monocrop and then incorporating it as a basal manure before the rice is transplanted; or transported to another site for use on upland crops; growing it as an intercrop and incorporating it as a top dressing manure after the rice is transplanted; or by growing it both as a monocrop and an intercrop. All these systems can be successful, but, and is common in agriculture, use of the green manure crop requires some adjustments in the management of both the green manure and the main crop. Monocrop Azolla is used in China and Vietnam during the winter and spring to produce nitrogen for the spring rice crop. The same technique is used to produce nitrogen for the early summer rice crop, but this is less common since the growth of Azolla pinnata is affected by high temperature and heavy pest attack during mid to late summer. Intercropped Azolla is usually grown with the rice in places where there is no time available in the cropping system for the monocropping of Azolla. Azolla as an intercrop Azolla will be initially introduced by hand or rotary rice weeder and then later killed by heavy shading and/or high temperatures, along with subsequent decomposition and release of nitrogen to the crop, which maximizes the grain production.

Environmental Requirements For Azolla: The ecology of Azolla in nature is still obscure.  The gross environmental requirements of Azolla are so interrelated that it is often difficult to single out any one or a combination of factors:

Moisture: Moisture is the fundamental requirement for an occurrence of Azolla. At a relative humidity of less than 60 percent, Azolla becomes dry and fragile and complete drying kills the fern. Although Azolla can grow on wet mud surfaces or moist peat litter, it prefers to grow in a free-floating state on the water surface. In shallow water, Azolla plant may touch the soil surface with its roots, but it can also grow in much deeper water where nutrients are absorbed completely from the aquatic environment while being afloat.

Light: Like all green plants, Azolla requires light for photosynthesis and production of organic carbon skeletons needed for cell synthesis. The acetylene reduction activity (ARA} of Azolla is considerably reduced when light intensities of 80,000 – 90,000 lx are reached at noon. The growth rate increases with increasing light intensity.

A temperature for Growth of Azolla: From traditional agricultural practices with Azolla, where it is grown as green manure in rice fields, the most favorable period for vegetative growth of Azolla was found to be August to February, during which period the mean daily temperature around 16° – 17°C. For optimum growth, A. caroliniana and A. Filiculoides prefer a lower temperature range of 5° – 20°c. Although Azolla pinnata is widely distributed in the tropics, it grows better only in cooler seasons. In India, Azolla pinnata grew well from July to December but it disappeared from the ponds in hot summer months (April – June}. In southern parts of China, Azolla grows most abundantly from February to May. In India, to be a typical winter annual plant. Its growth in ponds started from July and reached a peak maximum in November – December. From April to June, Azolla was completely absent. Thus, Azolla grows over a wide range of temperatures of 14° to 40°c. However, the optimum temperature for growth is around 20°-30°c.

Effect of pH:  The optimum pH range of Azolla is slightly on the acidic side of 4. 5 _ 7. 0. Maximum growth and biomass production are possible at pH 6.5, pH 5.5 was optimum for the growth of Azolla.

How Azolla Increases Yield of  Paddy

For growing paddy crop, less than 5% of the nitrogen delivered by Azolla immediately. The remaining 95% nitrogen remains in the Azolla’s biomass will be utilized until the plants die. Once the Azolla plant decomposes, its organic nitrogen will be mineralized and released as ammonia, which is readily available as a biofertilizer for the growing rice plants.

There are methods available to maximize Azolla’s nitrogen fertilization, with the result that Azolla now has enormous potential to increase rice production worldwide.

When you cultivate paddy with the chemical fertilizers, we spend approximately Rs.1,500 per acre. And with Azolla, the cost of cultivation can come down to 25%. Azolla can increase the paddy yield by 30-40%.

Farmers can create their own nursery for growing this fern. The field for growing Azolla should be ploughed, levelled, irrigated, and we should form small ponds. And it needs 15-20 cm of standing water in the fields. And the farmer may need green Azolla at the rate of 20 kg per hectare, and it should be mixed with fresh cow dung and then released into the pond.

Read: Soil pH Importance in Agriculture.

Last Updated: February 4, 2019
Author: Jagdish

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