Shelf-life of Biofertilizers: An Accord between Formulations and Genetics

Abstract

To meet the steady demand of food supply, application of fertilizer is indispensable in modern agriculture. Role of fertilizers has already been proven by many countries with green revolution and by attaining food self-sufficiency within short period of time. Actually, application of synthetic/chemical fertilizers not only supplies essential nutrients to food crops but also provides them in an easily available manner. Therefore, these fertilizers can quickly enhance the growth and productivity of food crops and are quick to gain popularity. However, extensive use of such fertilizer leads to serious environmental concerns. Nitrate leaching and surface/ground water pollution due to increased use of fertilizer is directly related to human health problems. Similarly, freshwater contamination by chemical fertilizer/fertilizer residue is one of the major causes of eutrophication. Likewise, increased greenhouse gas emission as well as heavy metal uptake and accumulation by food crop could be considered as other environmental problems emerged due to synthetic fertilizers [1]. Moreover, chemical fertilizer could eliminate the beneficial microbial as well as insect community of soil. Alternatively, many of these problems can be surmounted by utilization of biofertilizers. It may not be a realistic idea to completely replace the chemical fertilizers by biofertilizer; however, biofertilizers have the potential to supplement the synthetic fertilizers and to significantly reduce its use. In general, biofertilizers are living microorganisms, unlike chemical fertilizers; they themselves are not the source of nutrients but can help the plants in accessing the nutrient available in its surrounding environment. The microorganisms commonly used as biofertilizers may be nitrogen fixing soil bacteria ( Rhizobium, Azotobacter), nitrogen-fixing cyanobacteria ( Anabaena), phosphate solubilizing bacteria (Pseudomonas putida) and arbuscular mycorrhizal fungi. Similarly, phyto-hormone (auxin) producing bacteria and cellulolytic microorganisms could also be part of biofertilizer formulation. When applied to the field, the activities (nitrogen fixation, phosphate solubilization, production of phytohormones) of the plants are benefited resulting in improved growth and productivity. Therefore, viability of these organisms during production, formulation, storage, transportation/distribution and field application is directly related to plant growth promoting potential of a biofertilizer formulation. The complaint from farmers regarding the efficiency of biofertilizer is not uncommon and improper storage and longer duration between production and field application could be the best explanation for such incidents. This limits their use due to compatibility, stability and survival issues under different soil conditions. Hence, improved shelf life could be the key for further popularization of biofertilizer application. Presently, a range of commercial biofertilizer formulations are available and different strategies have been applied to ensure maximum viability of the microorganisms used in such formulations. These strategies comprise: (i) optimization of biofertilizer formulation, (ii) application of thermo-tolerant/drought-tolerant/genetically modified strains and, (iii) application of liquid biofertilizer. For convenience of application, a carrier material is used as a vehicle for the microorganisms to be used as biofertilizer. Moreover, such materials may have a role in maintaining the viability (shelf-life) of the microorganisms prior