Influence of Bacillus megaterium and pH on the solubility of Sokoto rock phosphate in soil

A research was carried out to determine the role of Bacillus megaterium and soil pH in relation to phosphorus availability in soil using Sokoto Rock Phosphate. The experiment was laid out in completely randomized design (CRD) in the laboratory using three (3) treatments 0, 5 and 10ml of Bacillus megaterium replicated three times. The results obtained shows that there is no significance difference at (p<0.05) in phosphorus concentration in relation to inoculants and uninoculated treatments at 0ml, 5ml and 10ml using Phosphorus solubilizing bacteria, significant difference was only observed in relation to soil pH at 4, 5 and 6 weeks after inoculation with the highest available phosphorus of 0.8gkg at 4 week with a mean pH of 7.5. The study suggest that although, the trend and relative effectiveness of microorganisms in the soil are very complicated and unpredictable, the B. megaterium is not always effective at phosphorus solubilization as was observed in so many research elsewhere which may be affected by many factors, such as Phoshate Solubilizing Bacteria (PSB) used, nutritional status of soil and environmental factors. Therefore it was concluded that pH is important in improving the activities of phosphate solubilizing organisms. More research is needed to identify, screen and characterize more PSB for their ultimate application under field conditions. INTRODUCTION Phosphorus (P) is second only to nitrogen as the most essential macro-nutrient required by plants (Srinivasan et al., 2012). It is a key nutrient for sustainable agricultural productivitywhich limits plant growth in many soils (Scevino et al., 2011). Despite the considerable addition of phosphorus to soil, the amount available for plant is usually low because, the availability of this nutrient for plants is limited by different chemical reactions especially in arid and semiarid soils (El-Gizawy and Mehasen 2009). Phosphorus is important in plants, especially in photosynthesis, membrane formation, carbon metabolism, energy generation, glycolysis, nucleic acid synthesis, respiration, enzyme activation and nitrogen fixation (Leidi and Rodriguez-Navarro, 2000; Wu et al., 2005). Low phosphorus availability of many tropical and subtropical soils in combination with insufficient P fertilizer applicationhas been identified as one of the major factors responsible for low yields. (Kretzchmar et al., 1991). Its deficiency affects root architecture, seed development and normal crop maturity (Borch et al., 1999, Williamson et al., 2001). It is a vital component of ATP, the "energy unit" of plants and of DNA, the genetic "memory unit" of all living things (Griffith, 1999). Phosphorus (P) is an essential macronutrient, being required by plants in relatively large quantities (approximately 0.2 to 0.8%) (Mengel and Kirkby, 1987; Mills and Jones, 1996). Therefore, many soils throughout the world are deficient in P because P-concentrations available to plants are generally low even at pH 6.5 where it is most soluble (Gyaneshwar et al., 2002). Thus P availability to crops in adequate amounts is a global issue and 30– 40% crop yield of the world’s arable land is limited by P availability (Vance et al., 2003). Inorganic forms of P are solubilized by a group of heterotrophic microorganisms by excreting organic acids that dissolves phosphatic minerals directly, releasing P into soil solution (He et al., 2002). Phosphate solubilizing bacteria (PSB) are being used as biofertilizers since 1950s in order to released phosphorus availability in soil (Krasilinikov, 1957). Rock phosphate is being considered as another source of phosphorus for reversing soil fertility depletion (Ghosal et al., 1998; White et al., 1999). Although, on one hand, insoluble organic compounds of phosphorus are largely unavailable to plants and many microorganisms can bring the phosphate into solution (Prosenjit et al., 1999; GuangLong et al., 1999). Therefore, the P-content in average soils is about 0.5% but only 0.1% of the total P is available to plants (Zou et al., 1992). It is recognized that the availability of phosphate in soils is a major factor limiting the productivity of many ecosystems (Daniels et al., 2009). There are various mechanisms by which microorganisms solubilize inorganic phosphate. It can be by secretion of organic acids (Goldstein, 1995) or by production of siderophores (Vassilev et al., 2006). Fortunately, various kinds of bacteria (Harris et al., 2006; Zaidi et al., 2009; Khan et al., 2010) and fungi (Whitelaw, 2000; Wakelin et al., 2007) have been http://dx.doi. org/10.4314/bajopas.v8i2. 1