Dear Dr. Naresh,

Nitrogen and Phosphorus stress conditions encourage the growth of blue-green algae. Heterocystous blue-green algae like Nostoc, Anabaena, Cylindrospermum etc. contribute in nitrogen fixation in rice fields.

Dr Rama Kant thank you for your contribution to the discussion

Cyanobacteria (Blue-Green Algae) are one of the major components of the nitrogen fixing biomass in paddy fields. The agricultural importance of cyanobacteria in rice cultivation is directly related with their ability to fix nitrogen and other positive effects for plants and soil. Besides pH, phosphorus availability is an important factor determining growth of BGA. In submerged soils and noted that BGA growth was closely related to the available P content of the soil. BGA are nutritious natural products rich in essential amino acids, γ-linolenic acid (GLA), fibers, B vitamins, calcium, phosphorous, iron, pigments such as β-carotene, xanthophylls, and chlorophyll, and other bioactive compounds. Nostoc, Anabaena, and Oscillatoria are nitrogen- fixing algae. All these are blue- green algae of group prokaryotes. Nowadays blue- green algae are called cyanobacteria because they are a type of bacteria that normally look green and sometimes turn bluish when scums are drying. Nitrogen and phosphorus are released in the environment by many human activities, including wastewater municipal plants, agriculture, and several industrial processes. These nutrients are a main limiting factor for algal growth in many water bodies. Besides CO2 and light, algae require nutrients to grow, nitrogen (N) and phosphorus (P) being the most important ones. These can be supplied in the form of agricultural fertilizer, which is simple, easily available but can be a significant cost factor. Algae require 10 to 40 times as much nitrogen as phosphorus to thrive and grow. In general, when the ratio of nitrogen to phosphorus is low, the microorganisms' growth is limited by nitrogen, and when the ratio is high, phosphorus controls the growth rate. Fertilizers’ can leach into fresh water, adding extra, unwanted nitrates. This will increase algal populations which can cause algal blooms. Excess nitrogen and phosphorus cause an overgrowth of algae in a short period of time, also called algae blooms. The overgrowth of algae consumes oxygen and blocks sunlight from underwater plants. When the algae eventually die, the oxygen in the water is consumed.