Potassium Solubilizing Microorganisms (KSMs) and Its Effect on Plant Growth Improvement
All the crops require nitrogen, phosphorus, and potassium macronutrients for proper plant growth, and addition of mineral fertilizers leads to impressive crop yield increases. Excessive application of chemical fertilizers increases the cost of crop production and causes environmental pollution. Many microorganisms inhabiting soil/rhizosphere play an important role in solubilization of bound form of soil minerals and enhance the availability of nutrients in the soil for plant growth and development. These plant growth promoting rhizobacteria, including N2 fixing, phosphate /potassium solubilizing bacteria, are being used as biofertilizers to minimize health hazards caused by the use of chemical fertilizers. About 90 98 of total potassium in soil exists in unavailable mineral form. Silicate minerals such as K feldspars and biotite are the most common minerals in the Earth's crust and are a source of inorganic nutrients in soils to provide optimal nutrition for crops. Recently, K solubilizing bacteria/fungi have been isolated from rhizosphere soil of different crops, which cause potassium solubilization by production of organic/inorganic acids or by production of polysaccharides. Efficient K solubilizing bacteria have been reported to enhance potassium uptake in plants leading to plant growth stimulation under pothouse and field conditions. These K solubilizing bacteria (KSB) could be applied as potential biofertilizers along with application of rock K materials to provide a continuous supply of available potassium for increasing the crop yield.