Developments in cyanobacterial biofertilizer

Abstract

Rice is the world's most important food crop as more than 40% of the world's population depends on rice as a major source of calories. Rice yield in India is about 1990 kg/ha against a maximum of 3346 kg/ha in Punjab. Though the rice yields in Punjab is highest in the country, it is quite low compared to China (5807 kg/ha). Such diversity in yields is due to insufficient use of fertilizer nitrogen. Nitrogen is present as elemental nitrogen in the atmosphere and constitutes more than 79 per cent of total gases. However, crop plants cannot utilize nitrogen in elemental form. On global level, out of 180 million tonnes of nitrogen added annually on the earth's surface, 2/3 is through biological processes, largely microbial activities. Cyanobacteria colonize rice fields and provide biologically fixed nitrogen to the rice crop to the extent of 25-30 kg nitrogen per hectare. In India, on an average, cyanobacteria accounts to about 33% of total algal flora of Indian rice field soils [66], whereas in some of the southern and eastern states this reaches up to 50%. Virtually all the dominant cyanobacteria in rice fields are nitrogen fixing. Apart from increase in yield and saving of fertilizer nitrogen, cyanobacterial inoculation improves the physico-chemical properties of soil, gradual build-up of residual soil nitrogen and carbon, improvement in soil pH and electrical conductivity. The grain quality in terms of protein content was improved. Our recent studies have shown that the cyanobacteria (Nostoc and Anabaena) were capable of forming associations with wheat roots grown in liquid culture. Probably, such cyanobacteria contribute nitrogen and growth promoting substances to plants in the rhizosphere. © Printed in India.