On soils with low available phosphorus, such as the Amazonian upland, the ability of rhizobium strains to solubilize inorganic phosphates is of extreme importance. The objective of this work was to determine the ability of rhizobium isolates from Amazonian soil to solubilize calcium and aluminum phosphate in laboratory, and their symbiotic efficiency to increase N and P contents in cowpea. The rhizobium isolates were evaluated on specific growth media during a period of 15 days, when solubilizing indexes (S.I.) were obtained. From the 205 isolates, 68 solubilized P-Ca and 47 solubilized P-Al, and 32 solubilized P-Ca as well as P-Al. Among the 14 isolates with highest solubilizing activities, eight isolates (INPA R820, INPA R825, INPA R843, INPA R894, INPA R914, INPA R917, INPA R969 and INPA R982) provided higher shoot P and N contents and dry matter.
phosphorus; Amazon; microbial ecology