Some isolated rhizobias, besides fixing N2, are also able to solubilize low soluble phosphates, making the P available both for plants and for themselves. Some factors like toxic Al and acidity, as in some Amazonian soils, may decrease the population of these microorganisms. The present study evaluated the nodulation ability, tolerance to acidity and toxic aluminum, as well as the ability to solubilize Ca and Al phosphates of rhizobia isolated from agricultural soils the municipality of from Presidente Figueiredo, AM. Samples of soil under agricultural cultivation were collected and used as a source of inoculum for the cowpea bean. Some rhizobia isolates were tested for tolerance to acidity and toxic Al, as well as to verify their abilities to solubilize phosphates. The soil samples contained rhizobia populations capable of inducing the nodulation and improving the aerial biomass of cowpea bean under acidity (pH 4,5) and alic (2 cmol c Al.L-1) conditions. The rhizobia population from the soil samples idnetified as INPA-PF2, INPA-PF3, INPA-PF4, INPA-PF5, INPA-PF13, INPA-PF15, INPA-PF22 and INPA-PF24 promoted increases of aerial biomass when compared to the control tratment (absence of inoculum). Twenty-five percent of the isolates were tolerant to acidity and 23% to Al. The Ca phosphate was solubilized by 39% of the isolated rhizobia. However, just one isolate presented high solubilization index. The Al phosphate solubilization ability was identified in 67% of the isolates. The majority of the isolates that solubilized Ca phosphate (76.5% of the lineages) also solubilized the Al phosphate.
Leguminosae; nitrogen; acidity; aluminum and phophate solubilization
