Contribution to a Sustainable Production of Alfalfa through the Management of Rhizospheric Microorganisms in Argentina, Chile and Uruguay

In the agricultural-livestock systems of Argentina, Chile and Uruguay, alfalfa occupies a high percentage of the cultivation area. It has been repeatedly cited that this species can maintain and even recover the nitrogen level of the soils where it grows. However, this statement could be true only if alfalfa is correctly associated with specific strains of high-efficiency rhizobia, capable of supplying the high nitrogen demand that the species requires due to its protein content. Currently, the alfalfa seed available in the participating countries of the Project is imported in a large percentage and much of it comes pre-inoculated with rhizobia strains whose efficiency and adaptation to local conditions is not always known. Even though inoculation is fairly widespread, the relative efficiency of biological nitrogen fixation (BNF) provided by nodular systems formed from introduced strains compared to native or naturalized strains is currently unknown.

Furthermore, although there are more or less complete collections of native rhizobia in the countries participating in the Project, the accessions do not represent all cultivation areas, nor are they characterized according to their ability to fix nitrogen in areas with and without soil restrictions. There are also no isolates from other rhizospheric microorganisms capable of improving biological fixation and/or plant growth (PGPB and NPR bacteria and phosphorus solubilizers). The objectives of this project were: a) quantify the relative efficiency in nitrogen fixation of nodular systems formed with different degrees of nodular occupation by introduced and native or naturalized strains, b) study the biodiversity in populations of native or naturalized rhizobia and select the better strains in different regions of the countries that make up the Project, c) characterize and select PGPR, NPR and P-solubilizing bacteria, which alone or co-inoculated with rhizobia improve alfalfa productivity, and d) generate normative criteria for the use of rhizospheric microorganisms that participate in the sustainability of alfalfa cultivation.