Abstract

REYES, Isbelia  and  VALERY, Alexis. Effect of soil fertility on microbiota and corn (Zea mays L.) growth promotion with Azotobacter spp.. Bioagro [online]. 2007, vol.19, n.3, pp.117-126. ISSN 1316-3361.

The study of microbial populations allows the evaluation of a soil fertility and its ecological condition. In this paper, the total and calcium phosphate solublizing culturable bacteria and fungi population densities were evaluated in the rhizosphere of wild and crop plants from five different soils of Táchira State. By changing the soil fertility with several chemical fertilizer treatments two Azotobacter strains were evaluated for the growth promotion of corn (Zea mays L.). The dilution plate and culture method were used for soil microbial determinations. The dry weight of corn plants was quantified in the assays using the Azotobacter strains MF1b and MF5, alone and in mixed culture with the chemical treatments of K, NK, PK, RK, NPK and NRK (R is phosphoric rock). It was found that the total microbial and phosphate solubilizing population densities showed changes according to the physical and chemicals conditions of the soil and to the type of each vegetal species. After the microbial densities of the soils, a low ratio rhizosphere/soil (R/S) was showed by one with good nutritional conditions in contraposition with other with high physical and chemical deterioration due to mine explotation. The Azotobacter strain MF1b increased significantly the dry weight of corn in a greenhouse assay with the chemical treatments NK and RK. It is concluded that this strain has a potential use in the sustainable agriculture.

Keywords : Microbial populations; phosphate solubilization; rhizosphere.