Occurrence of Azospirillum brasilense in soils amended with swine manure

Restriction analysis of amplified 16S rDNA from bacterial strains isolated from soil was used to evaluate the effects of swine manure and urea fertilisation on indigenous populations of the plant growth promoting bacterium, Azospirillum brasilense, in corncultivated experimental plots. Several operational taxonomic units (OTUs) were found among the isolates. One of them, identified as A. brasilense, was found only in the control and in the organically amended plots, while treatment with urea reduced the presence of this species to under the detection threshold. Neither the organic nor the chemical treatment reduced the general biodiversity of the sampled soils, which was defined by the number of different OTUs within each plot. The spreading of pig slurry seems to be a good management practice in corn-cultivated agrosystems, as it does not affect the presence of A. brasilense.