Microbial Biofertilizers: Types and Applications

Abstract

The increased dependency of modern agriculture on excessive synthetic input of chemical fertilizers has caused several environmental problems related to greenhouse effect, soil deterioration, and air and water pollution. Furthermore, there is an imperative need for viable agricultural practices on a global level with reduced energy and environmental problems, for adequate cost-efficient production of food for the increasing human population. Consequently, biofertilizers containing microorganisms like bacteria, fungi, and algae have been suggested as viable solutions for large-scale agricultural practices which not only are natural, ecofriendly, and economical but also maintain soil structure as well as biodiversity of agricultural land. Besides providing nutrient enrichment to the soil, microbial biofertilizers promote plant growth by increasing efficient uptake or availability of nutrients for the plants and by suppressing soilborne diseases. Biofertilizers supplement nutrients mainly by fixation of atmospheric nitrogen, by phosphorus solubilization, and by synthesizing plant growth-promoting substances. The nitrogen-fixing bacteria of the rhizobia and other groups are used for growth promotion of legumes and additional crops. In addition, blue-green algae (BGA) as well as Azolla subsidize in the nitrogen budget of practicable agriculture. Arbuscular mycorrhizal fungi are important for the uptake of phosphorus and several other minerals in many plants. Phosphorus-solubilizing bacteria like Azotobacter and Azospirillum that fix atmospheric nitrogen can increase the solubility and availability of phosphorus to plants and, thus, crop yield. Further, Azospirillum provides additional benefits such as the production of growth-promoting substances, disease resistance, and drought tolerance. Thus, application of microbial biofertilizers is an effective approach in increasing and maintaining the nutrient economy of soil, thereby reducing the use of chemical fertilizers, for a proficient and sustainable agriculture.