Análisis del valor agronómico de biofertilizantes basados en rizobios, en cultivos extensivos de cereal

Abstract

In the present times, the scientist focus the study of the soil ecosystem in the transformations and interactions leaded by the microorganisms. Moreover, recent studies have shown that such microorganisms can improve the nutrients absorption by plants, and therefore they enhance the fertilizers use efficiency. As efficient plant nutrition depends on the capacity of soil to supply nutrients in the form and quantity required by the crops, whenever the soil cannot efficiently provide the nutrients to the crop, an external application of mineral fertilizers is needed. In this research, we have analyzed the use of biofertilizers based in rhizosphere microorganisms, along with conventional fertilizers in winter cereals, in order to optimize the production of crops and minimize losses of fertilizer to the environment. The aim of this study was to analyze the agronomic value of the designed biofertilizers in extensive cereal crops. The research plan was the following: Four strains were selected from a Rhizobium leguminosarum strains collection, isolated from soils located in Castilla and León. The criteria for selection was the degree of expression of several Plant Growth Promoting activities, analyzed in vitro. Formulations with such strains were tested firstly in microcosm and thereafter in field. At the same time, we analyzed if the symbiosis between the root plant and the bacteria was established at the rizospheric or endophytic level. Finally, we studied the economic and environmental impact of the designed biofertilizers. The selection of microorganisms was based on the following Plant Growth Promoting (PGP) activities, evaluated in vitro: indoleacetic acid production, solubilization of mineral phosphorus, siderophore production and ACC deaminase activity. Four strains namely B4, C4, A7 and D7 were selected. The microcosm tests in wheat and barley plants, using the selected strains as inoculants, showed a plant growth promotion effect of the inoculation in the plants, because the inoculated treatments produced higher fresh and dry aerial biomass (weight), and also higher N concentration and total N content in the aerial biomass, compared to a non-inoculated control. The highest dry aerial biomass was produced by the strain A7, which was selected on the basis of its ACC deaminase activity, and the higher N concentration was produced by C4, selected for the level of IAA production. The same trial revealed that the best result were obtained with intermediate microorganisms dose. As a whole, the field trials confirmed the microcosm results, demonstrating that treatments inoculated with rhizobia improved the aerial biomass production and the crop yield, in wheat and barley crops. Moreover the symbiotic relation between the rhizobia strains and the barley root was elucidated using microscopy techniques with rhizobia marked with the green fluorescent protein GFP. We arrived to the conclusion that the colonization of barley roots by Rhizobium leguminosarum was established at the rhizosphere level. Finally, the economic and environmental analysis showed that the biofertilization of cereals with rhizobia improved the gross margin of the farmer between 63 and 127 € per ha. Moreover, there is a slight reduction of the carbon footprint in the global process of cereal production