Soil is a harbor of microorganisms like algae, fungi, bacteria and some other organisms. The blue green alga is the most common type algae which are found in the soil. They are the chief organism that fixes the nitrogen in the rice field. They are capable of fixing the atmospheric nitrogen into their bodies. It increases the soil fertility and improves the growth of the crop plants thereby increases the output of agriculture.
Some important algae are oscillatoria, Nostoc, Anabaena, Aulosira and Spirulina. Some of the algae are applied to the field with the nitrogen fixing species which will increase the nitrogen content of the soil. The blue green algae is also used in the reclamation of barren land, alkaline soil there by it can be brought into productive land. The successive application will reduce the intensity of alkalinity and will increase the fertility of the soil. Large members of brown algae and red algae are used as organic fertilizers. Commonly in India Turbinaria is used as a fertilizer around palm trees.