Selection of dominant bacteria for phosphate liberation in calcareous soil

B2 and 1367 were identified as two best bacteria to promote phosphate liberation from crops rhizos phere．During incubation in culture media with B2 and 1367，the phosphate dissolved circles in plate culture，i．e．D／d values ，are 5．1 and 3．8 respectively for B2 and 1367．More than one kind of organic acids，including malic acid，malonic acid，oxalic acid and lactic acid，are produced and the total amount of acid is 28．25 and 19．78 times of control，respectively．Further the pH of culture media decline 2．3 and 1．1 units，respectively．W hen four soil samples，collected from different areas，are incubated with the above culture med ia for 20 days under the conditions of constant temperature and humidity，available phosphate in four soil samples is enhanced by B2 and 1367．Available phosphate contents are 2．64，3．04，1．71 and 2．20 times of four control samples ，respectively when the abo ve four soil samples are incubated with B2；whereas available phosphate contents are 2．12，1．90，1．35 and 1．78 times of four control samples ，respectively when the abo ve four soil samples are incubatedwith 1367．Also it is found that phosphate lyolysis is positively related to the available number of bacteria an d phosphatase activity in soil．