OPTIMUM CONDITIONS FOR GROWING AZOLLA
English
Carrapiço and Pereira (2009) found that the IRRI2 medium, created by the International Rice Research Institute (IRRI), is the most effective for growing Azolla. Table 1 shows the nutrient concentrations in the IRRI2 medium, as reported by Francisco Carrapiço from the University of Lisbon.
Water acidity (pH)
Azolla thrives in water with a pH between 4 and 7. This range supports optimal growth and nitrogen fixation. Water that is too acidic or too alkaline can hinder Azolla’s development, affecting its efficiency as a biofertilizer. Maintaining the ideal pH is crucial for healthy Azolla cultivation.
Temperature
Azolla can tolerate a wide range of temperatures, with some species surviving as low as -5°C. However, growth diminishes above 35°C, and no species can endure temperatures above 45°C for extended periods. Optimal temperatures for most Azolla species are between 18°C and 28°C, though species like A. pinnata, A. mexicana, and A. caroliniana can thrive up to 30°C.
Light
Light influences both photosynthesis and nitrogenase activity in Azolla and Anabaena. Azolla species generally thrive in partial sunlight rather than full sun, except at high latitudes during spring. Experimental results can vary based on the latitude where they are conducted. Under intense sunlight, Azolla fronds turn brick red, while low light conditions, such as those under dense rice growth, can cause Azolla to suffer or die.
Photoperiod
Azolla generally requires a photoperiod of around 12 to 14 hours of light daily for optimal growth. This duration supports effective photosynthesis and nitrogen fixation. While Azolla can adapt to varying light conditions, consistent photoperiods ensure healthy development. Insufficient light or extended periods of darkness can hinder growth and reduce the efficiency of nitrogen fixation.
Minerals
Azolla needs all the essential elements required by other plants, along with molybdenum, which is crucial for nitrogenase activity, and cobalt, necessary for Anabaena's nitrogen fixation. Typically, nutrients should be available in the water, though Azolla can absorb some from the soil in very shallow water. Maintaining adequate nutrient levels throughout the growth period is essential for optimal development.
Nitrogen
Azolla relies on nitrogen fixation to thrive, using its symbiotic relationship with the blue-green alga Anabaena to convert atmospheric nitrogen into a usable form. This process provides Azolla with the nitrogen it needs for growth. Adequate nitrogen levels are crucial for healthy Azolla development, and maintaining optimal conditions ensures effective nitrogen fixation and overall plant health.
Phosphorus
Phosphorus is the most critical and often limiting nutrient for Azolla growth. Deficiency typically results in smaller, less vigorous plants, which may turn pink to deep red and become fragile, with excessively long roots. Adequate phosphorus levels are essential to ensure robust and healthy Azolla development.
Iron
Iron is a key limiting element in Azolla’s growth, as it is crucial for nitrogenase function. Plants deficient in iron turn yellow due to a lack of chlorophyll, and their roots become thin and whitish. Adequate iron is essential for maintaining healthy Azolla and effective nitrogen fixation.
Calcium
Calcium deficiency in Azolla leads to intense reddening of the dorsal lobes, with fragmented fronds. The roots become short, thin, and lighter in color. Ensuring adequate calcium is crucial for maintaining healthy Azolla growth and preventing these symptoms.
Potassium
In potassium-deficient Azolla, the fronds turn yellowish-brown, the roots become dark brown, and growth is stunted. Adequate potassium is essential for preventing these symptoms and ensuring healthy Azolla development.
Optimum threshold nutrients levels
Optimum nutrient levels for Azolla include adequate phosphorus, iron, calcium, and potassium. Phosphorus promotes vigorous growth, iron supports nitrogenase function, calcium prevents reddening and fragmentation, and potassium ensures healthy frond color and root development.
Threshold macronutrients levels for azolla growth.
P: 0.03 mmol 1-1
K: 0.4 mmol 1-1
Mg: 0.4 mmol 1-1
Ca: 0.5 mmol 1-1
Threshold macronutrients levels for full nitrogenase activity:
P: 0.03 mmol 1-1
K: 0.6 mmol 1-1
Mg: 0.5 mmol 1-1
Ca: 0.5 mmol 1-1
Threshold levels of the micronutrients for azolla growth:
Fe: 50 g1-1
Mn: 20g1-1
Mo: 0.3g1-1
B: 30g1-1
Pests
Azolla is vulnerable to pests like lepidopterous and dipterous insects, as well as fungal diseases, especially during hot, humid conditions. Snails are also a common pest affecting Azolla, particularly in rice fields.
Pesticides
When managing pests in Azolla, it is essential to use appropriate pesticides carefully to avoid harming the plants. Commonly used options include insecticides targeting specific pests like snails and caterpillars, and fungicides for fungal diseases. Always follow application guidelines to minimize environmental impact and ensure the health of Azolla and surrounding ecosystems.