Biofertilizers in Fruit Crops - a Review

BiofertiJizers are microbial preparations containing living cells of different microorganisms which have the ability to mobilize plant nutrients in soil from unusable to usable form through biological process. They are environmental friendly and play significant role in crop production. Previollsly it is mainly used for field crops but now-a-days it is used for fruit crops also. Biofertilizers are able to fix 20-200 kg Nlha/year, solubilize P in the range of 30-50 kg Pprfhalyear and mobilizes P, Zn, Fe, Mo to varying extent. Biofertilizers are use in live formulation of beneficial microorganism which on application to seed, root or soil, mobilize the availability of nutrients particularly by their biological activity and help to build up the lost microflora and in turn improve the soil health in.general. Thus the use of biofertiltzer is increasing day by day due to increase in the price of chemical fertilizers, its beneficial effect on soil health and increase in production of crop. Biofertilizer playa very significant role in improving soil fertility by fixing atmospheric nitrogen both in association with plant roots and without it. It solubilizes insoluble soil phosphate and produces plant growth substances in the soil. They are environmented friendly playing a significant role in crop production. The soil lose its biological dynamism owing to repeated and indiscriminate use of inorganic source of fertilizer. The global mendate (Dorrel and Besson, 1996) today is to use organic source of plant nutrients to restore the soil health. The fertilizers are not only short in supply but costly too and produced at the cost of irreparable loss of non-renewable energy. Biof~rtilizers are able to fix atmospheric nitrogen in the range of 20200 kg/ha,lyear, solubilize P in the range of 3050 kg PpJha,lyear; mobilize p"Zn, Fe, Mo to varying extent. They also help host plants to resist diseases and withstand stress conditions by different mechanism which vary depending upon the type of biofertilizer agent involved. Nitrogen fixing bacteria and phosphate solubilizer are the main biofertilizers for horticultural crops. These micro-organisms are either free living in soil or symbiotic with plants and contribute directly or indirectly towards nitrogen and phosphorus nutrition of the plants. According to Subba Rao (1998), bioferlllizers are otherwise called microbial inoculants, are the carrier based preparation containing beneficial microorganisms designed to improve the soil fertility and help the plant growth by their increased number and biological activity in the rhizosphere. Motsara et aJ. (1995) reported that inoculation of Azospiril1um and Azotobacter exerted beneficial effect on yield with varying physiological activities, including synthesis of plant growth promoting substances. Bioferdlizer is a cost effective renewable energy source and plays a crucial role in reducing the inorganic fertilizer application and at the same time increasing the crop yield besides maintaining soil fertility. In other words, biofertilizers are based on renewable energy sources and are ecofrienclly compared to commercial fertilizers (Verma and Bhattacharyya, 1994). In the recent years, there is an urgent need to supplement the fossil fuel based inorganic fertilizers not only due to the hike in prices of chemical fertilizers but also a ne.ed is felt to maintain long term soil productivity and ecological sustainability. MECHANISM OF BIOFERTILIZERS The mechanism involved in the plant growth promotion by biological inoculants was given by (Okon, 1985). 70 AGRICULTURAL REVIEWS i) Increased availability and uptake of nutrients Through biological nitrogen fixation, solubilization of insoluble phosphates and mobilization of plant nutrients in more quantities are made available for crop plants by the root associated organisms. Increased nitrogen, phosphorous and potassium content of inoculated plants at different stages of crop growth have been found resulting in significant increase in grain yield. ii) Production of plant growth promoting