Sustainable production of alfalfa

Management of rhizospheric microorganisms

Context of the story

In Argentina, 6 million hectares of alfalfa are cultivated, placing this country as the world’s second-largest producer, after the US. In Chile and Uruguay, the cultivated areas are 250,000 and 100,000 ha respectively, which represents approximately 30% of the potential arable area of these countries. The improper handling of alfalfa can cause a rapid and constant loss of the nitrogen fertility of the soil, if there is no partial nitrogen recycling system coupled with an efficient system of biological nitrogen fixation by association with specific rhizobia. Therefore, the property of alfalfa to maintain soil fertility largely depends on its ability to incorporate nitrogen from the atmosphere.

The Implemented Initiative

The objectives of the project were: 1) To quantify the relative efficiency in nitrogen fixation of nodular systems formed by introduced strains and by native or naturalized strains, with different degrees of nodular occupation. 2) Study the biodiversity in populations of native or naturalized rhizobia and select the best strains in different regions of the countries that make up the Project. 3) Characterize and select PGPR and NPR bacteria that, alone or co-inoculated with rhizobia, improve the productivity of alfalfa. 4) Generate normative criteria for the use of rhizospheric microorganisms that participate in the sustainability of the alfalfa crop.

"Compared with other species, alfalfa forage has a higher protein content and, consequently, high nitrogen requirements."

— Roberto W. Racca.

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Type of project

Agronomic Practices

Sustainable intensification

Strategy 1. Resilient farms

Applied

Technological

Cattle raising, Natural resources

Family agriculture

Results

It was concluded that the differences in forage production between the inoculated and non-inoculated crop are evidenced only when: 1) the pre-existing population of rhizobia in the soil is low, 2) there is low availability of organic matter in the soil or 3) there is no other limiting factor. Regarding the goal of collection of strains, it was observed that of 100 isolates from Argentina, 74 from Chile and 23 from Uruguay, and after the infectivity and efficiency tests, 8 of those from Argentina were more efficient than the control strain; 10 of those from Chile also outperformed their respective control, while two were shown to be inefficient or parasitic. Regarding the PGPR strains, it was observed that in Uruguay and Chile the solubilizers of P prevail, while the predominant ones in Argentina are those of biocontroller action.