This study investigated the effectiveness of several microorganisms, such as a Bacillus megaterium strain and/or an autochthonous consortium of arbuscular mycorrhizal fungi (AMF) on plant growth and drought tolerance in a natural semiarid soil. The effect of treated Aspergillus niger residue from sugar beet was also evaluated in non-inoculated and inoculated plants. Results from three successive harvests allowed us to determine the persistence along the time of beneficial effects of these treatments under natural drought conditions. Biomass production and nutrition were more increased by the transformed residue than concomitantly decreased antioxidant enzymatic activities under drought. The microbial inoculants assayed contributed to plant drought tolerance through strategies such as increased nutrition (particularly K+), hydric content and by decreasing stomatal conductance and antioxidant enzymatic activities. Similar microbial-mediated effects were confirmed at each harvest. The effectiveness of bacterial inoculation under drought conditions in natural soil has been almost unexplored. Here, the interactive effect of these bacteria with an AMF consortium maximized plant growth, water content and C, K, Ca and Mg content. A relevant result is the greater effectiveness of the bacteria when inoculated in residue amended soil that promoted plant growth and hydric content and decreased most antioxidant activities to a greater extent than AMF inoculation. B. megaterium (without compost) also affected root growth, physiological and biochemical plant values involved in the adaptative plant drought response. The ability of B. megaterium in axenic medium to maintain indole acetic acid (IAA) like molecules and to increase proline production under osmotic stress conditions indicated the drought tolerance of this strain. In this study the management of natural resources, such as selected and drought adapted soil microorganisms and A. niger treated agrowaste resulted determinant for enhancing plant performance in an arid degraded soil. E. Armada was financed by Ministerio de Ciencia e Innovación. This work was carried out in the framework of the project reference AGL2009-12530-C02-02. Peer reviewed