The coming decades will be the challenge for agriculture to meet the world’s increasing demand for food in a sustainable way. Due to declining soil fertility and mismanagement of plant nutrients the task has become more difficult. Moreover, limited availability of additional land for crop production along with declining yield for major food crops have concerned the agriculturist to feed the world’s bursting population which will exceed 12.5 billion by the year 2030. Therefore, future strategies for increasing agricultural productivity have to be focused on using available nutrient resources more effectively, judiciously and efficiently.
Here Integrated Nutrient Management (INM) will play an important role in increasing agricultural production and also safeguarding the environment for future generation. INM is a strategy that incorporates both synthetic and biological plant nutrient in a judicious manner for attaining higher crop productivity as well as sustaining soil health for years to come.

 Azolla Bio-fertilizer for flooded rice: One of the most important bio-fertilizers for wetland rice is the water fern Azolla and the blue green algae also known as floating nitrogen fertilizer factories. Both can grow alongside paddy. Azolla can also be used for green manuring, which could contribute from 20 to 60 kg per hectare N. Azolla is considered an efficient scavenger for potassium and serves as a source of K for rice crops.

Azolla:- Azolla is a free floating water fern that floats in water. It is regarded as the “Soybean plant in rice fields” because it can fix and assimilate nitrogen owing to association for Cyanobacteria- Anabaena azollae in the dorsal cavities of Azolla leaf (Moore, 1969). Azolla is found in ponds, ditches and wetlands of warm-temperate and tropical regions throughout the world. The Azolla plant is triangular or polygonal in shape and floats in water surface individually or in mats. The plant has alternately arranged branches and adventitious roots remaining hanging in standing water. Azolla multiples vegetatively a sexually by producing spores. Vegetative reproduction is most common and continues at all times. Presently, six species of Azolla have been recognized worldwide. These are: Azolla filiculoides; A. caroliniana; A. Mexicana; A. microphylla; A. pinnata and A. nilotica. Each individual species has distinct geographic origin. For example- A. pinnata is native to South East Asia, Oceania and Coastal Africa.

Importance of Azolla: Cultivation of Azolla as biofertilizer input for rice has been recognized in many Asian countries like China, Vietnam, Phillippines, Sri Lanka and sporadically in India. Rice growing areas of these countries has been evincing increased interest in the use of Azolla as an alternate N source or as a supplement to commercial nitrogen fertilizers. Potentialities of Azolla as alternate green manure can contribute 40-60 kg N/ha per rice crop with significant increase in yield and productivity. Moreover, due its rapid  decomposition nature, Azolla can add considerable amount of organic matter in the soil subsequently releasing other essential nutrients like K, Ca and Mg for better utilization by rice crop. Some multiple benefits of Azolla are-

1. It acts as biological herbicide depressing germination of weeds.

2. Accumulate nutrients from flood water and release to rice crop after decomposition.

3. Due to its high protein content (20-30% on dry weight basis) it can be used as organic feed substitute for livestock.

4. Due to its rapid decomposing nature, Azolla can be used as manure for dryland crops, vegetable and ornamental plants.

5. On dry weight basis Azolla contains Nitrogen (5%); Phosphorus (0.5%); Potassium (2-4.5%); Calcium (0.1-1%); Magnesium (0.65%); Manganese (0.16%); Iron (0.26%); Crude fat (3-3.3%) Sugar (3.4-3.5%); Ash (10%).

Methods of Azolla cultivation

a). Homestead method: Maintenance of fresh Azolla inoculums and off-season starter dose is very essential prior to mass multiplication in the field. In this regard, a low cost method for round the year maintenance of Azolla (A. caroliniana) under homested condition has been developed by Assam Agricultural University. The method involves preparation of pit size of 2 m length, 1 m wide and 20 cm depth and covering with plastic gunnies followed by lining with 0.5 mm polythene sheet. Rise the surrounding by mud plastering and pour water up to 10 cm. Mix ingredients (SSP 10 gm + MOP 10 gm + 100 gm dry sieved cow dung) and apply to each pit. Inoculate fresh Azolla @ 400 gm/pit and allow multiplying for at least 15 days and harvest.

b). Field method: Prepare and level the field uniformly. Divide the field into 20 m x 5 m providing suitable bund and irrigation channel. Maintain water up to 10 cm gm SSP in each plot. Harvest Azolla at 15-20 days after inoculation.
INM package for rice with Azolla
By growing  Azolla in separate plot: 1/10 of a hectare is needed to produce 20 tons/ha Azolla manure for incorporation in the rice field.

Dual culturing of Azolla with rice: This method is most feasible practice under controlled irrigation system. In this method, fresh Azolla multiplied elsewhere is applied @ 500 kg/ha as basal at 7-10 days after transplanting of rice and allowed to grow for 15-20 days and thereafter incorporated. The remaining Azolla again multiplies and grow to full bloom in another 15-20 days which needs to be incorporated again.

Benefits:

  •    Basal application of Azolla manure @ 10 tons/ha increase soil nitrogen by 50-60 kg/ha and reduce 30-35 kg fertilizer nitrogen required by rice.
  •   Dual cropping with rice enrich soil nitrogen by 50 kg/ha and reduce N requirement by 20-30 kg/ha.
  •    Use of Azolla increase rice yield by 20 to 30%.
  •    The nitrogen obtained from Azolla is enough to support yield of 3 to 3.5 tons paddy/ha.