Inoculation methods of Rhizobium tropici and Azospirillum brasilense on common bean crop: root growth, biological nitrogen fixation and grain yield

• Grant number: 18/15930-7
• Support type: Scholarships in Brazil - Doctorate
• Effective date (Start): June 01, 2019
• Effective date (End): July 28, 2021
• Field of knowledge: Agronomical Sciences - Agronomy - Crop Science
• Principal researcher: Rogério Peres Soratto
• Grantee: Amanda Prado Gilabel
• Home Institution: Faculdade de Ciências Agronômicas (FCA). Universidade Estadual Paulista (UNESP). Campus de Botucatu. Botucatu , SP, Brazil

Abstract

Among the nutrients required by common bean (Phaseolus vulgaris L.), nitrogen (N) is the most taken up. Nitrogen fertilizers, a major source of N for crop, have high economic and energetic costs, low efficiency of use by plants and environmental risk. Thus, there is a great interest in strategies that aimed at reducing the use of fertilizers and consequently improvements in sustainability in agricultural areas. In that sense, a technique that is beginning to be explored in the bean crop is co-inoculation, which is the association of Azospirillum with the Rhizobium. It is possible that some bacteria, among which those of the genus Azospirillum, benefit plant growth by a combination of several mechanisms. However, inoculation/co-inoculation can be carried out in different ways, generating different responses in the growth, development and production of the crops. The aim of this study is to evaluate the inoculation of symbiotic bacteria (Rhizobium) and associative bacteria (Azospirillum), in isolated or combined way, in growth, nodulation, biological nitrogen fixation, mineral nutrition and grain yield of common bean. The research will be conducted at the Experimental Farm Lageado (Site 1) in Botucatu-SP, during the growing seasons 2018/2019 and 2019/2020, and in commercial bean production area (Site 2) in Paranapanema-SP, during the growing season 2019/2020. The experiments will be conducted in the design of randomized blocks with four replications. The treatments will consist of three methods of inoculation with R. tropici, combined or not with four methods of inoculation with A. brasilense, plus one control with N, in factorial scheme 3x4 + 1, totaling 13 treatments. In two experiments, two additional treatments will be included relating to mineral N supplying (40 and 80 kg ha-1 of N). In the phenological stages V4, R6 and R8 the bean plants will be evaluated for the nodule number and dry weigh, root growth, roots and shoot dry matter, N content and accumulation in the shoot and ureides content in the petioles. In the R6 stage, evaluations related to chlorophyll relative index, foliar diagnosis and Biological Nitrogen Fixation (BNF) estimation by the 15N natural abundance technique. On the occasion of the plant cycle closure will be evaluated the production components, grain yield, protein content in grains and protein yield. The results will be submitted to analysis of variance by the test F. The means of the factorial's treatments will be compared by Tukey's Test at 5% probability. Using the Dunnett's Test (Pd0.05), the orthogonal contrasts of the factorial's treatments will be compared with the control. With this study we will know if the co-inoculation stimulates the root surface growth and consequently increases the soil volume explored by the same, and also if this technique potentiates the BNF by Rhizobium through increased nodulation and/or nodule activity. It will also be possible to define a solid positioning on the method(s) of inoculation which provide greater bacteria's efficiency. (AU)