<P> Other types of bacteria, so - called phosphate - solubilizing bacteria, such as Pantoea agglomerans strain P5 or Pseudomonas putida strain P13, are able to solubilize the insoluble phosphate from organic and inorganic phosphate sources . In fact, due to immobilization of phosphate by mineral ions such as Fe, Al and Ca or organic acids, the rate of available phosphate (P) in soil is well below plant needs . In addition, chemical P fertilizers are also immobilized in the soil, immediately, so that less than 20 percent of added fertilizer is absorbed by plants . Therefore, reduction in P resources, on one hand, and environmental pollutions resulting from both production and applications of chemical P fertilizer, on the other hand, have already demanded the use of phosphate - solubilizing bacteria or phosphate bio-fertilizers . </P> <P> Benefits of bio-fertilizers are: </P> <Ol> <Li> These are means of fixing the nutrient availability in the soil . </Li> <Li> Since a bio-fertilizer is technically living, it can symbiotically associate with plant roots . Involved microorganisms could readily and safely convert complex organic material into simple compounds, so that they are easily taken up by the plants . Microorganism function is in long duration, causing improvement of the soil fertility . It maintains the natural habitat of the soil . It increases crop yield by 20 - 30%, replaces chemical nitrogen and phosphorus by 30%, and stimulates plant growth . It can also provide protection against drought and some soil - borne diseases . </Li> <Li> Bio-fertilizers are cost - effective relative to chemical fertilizers . They have lower manufacturing costs, especially regarding nitrogen and phosphorus use . </Li> </Ol> <Li> These are means of fixing the nutrient availability in the soil . </Li>

Azotobacter is a useful biofertilizer in which crop