Quantificação da contribuição de bactérias diazotróficas na absorção de nitrogênio pela cultura do milho

Abstract

The endophytic diazotrophic bacteria associated with grasses have great potential for use as biofertilizers, being that the efficient use of nitrogen is an essential factor for a sustainable agriculture and to the global agribusiness. Given the above, the objective of this thesis was to quantify the contribution of diazotrophic bacteria in nitrogen uptake by corn culture in a distroférrico Red Latosol, evaluating the effects of inoculation of diazotrophic bacteria associated to nitrogen fertilization on productivity of maize grains, nitrogen uptake by corn, the accumulation of nutrients by culture, nitrogen use efficiency and the contribution of biological nitrogen fixation. The first study was carried out in the experimental field of Embrapa Agropecuária Oeste, in Dourados-MS. the experimental design used was randomized blocks, with nine treatments and six replications. The parameters evaluated were: height of the plants, culm diameter, height of insertion of cob, cob mass, spike length, number of rows of grains per spike, number of grains per spike, spike base diameter, mass of thousand grains, dry mass of the aerial part, productivity, chlorophyll content, content of nutrients in leaves and grains of maize, amount of N accumulated in plant, percentage of N in the plant from the fertilizer, quantity of N in the plant from the fertilizer, efficiency of utilization of the N applied as fertilizer and the percentage of biological fixation of N. The second study was conducted in a greenhouse at the Faculty of agricultural sciences of the University Federal of Great Dourados, in Dourados-MS. the experimental design used was the completely randomized design in factorial scheme 3 x 2 x 2, and three hybrids of corn: Maximus, P3646H and BRS3035; inoculated and non-inoculated plants and two doses of nitrogen: 0.0 and 80 kg ha-1, with four replicates. To 35 days after emergence, plant height was determined, the culm diameter, the chlorophyll content, root length, root volume, the concentration of N in the shoot and root, as well as the efficiency of absorption and use of N. The third survey was conducted in the experimental area of the Faculty of agricultural sciences of the University Federal of Great Dourados, in Dourados-MS. the experimental design used was randomized blocks with five repetitions. Treatments were arranged in factorial arrangement 2 x 5, namely the absence and presence of Herbaspirillum seropedicae and inoculation with five nitrogen doses (0, 48, 72, 96 and 120 kg ha-1). The parameters evaluated were: height of insertion of cob, culm diameter, masss of spike, spike length, number of rows of grains per spike, number of grains per spike, spike base diameter, mass of thousand grains, dry mass of the aerial part, productivity, chlorophyll content and N content in the leaves of corn. The obtained results allowed concluding that the nitrogen fertilization associated with inoculation with Azospirillum brasilense and Herbaspirillum seropedicae positively influenced the mass of cob, COB diameter, number of grain per Spike, aerial dry mass, productivity and chlorophyll content of corn plants.The levels of N, P, K, and Zn in the leaves of maize increased by nitrogen fertilization and inoculation with Azospirillum brasilense and 14 Herbaspirillum seropedicae. The inoculation with Azospirillum brasilense without nitrogen fertilization promoted greater accumulation of N, K, Ca and Mg in grains in relation to the treatments inoculated with Azospirillum brasilense and Herbaspirillum seropedicae and composted with 30 and 120 kg ha-1 of N. The inoculation of Azospirillum brasilense and Herbaspirillum seropedicae or associated with nitrogen fertilization can provide a reduction in use of synthetic nitrogen fertilizers on maize culture. The technique of natural abundance of 15N, inoculation with Azospirillum brasilense and Herbaspirillum seropedicae contributes on average with 19.40% and 9.49%, respectively, of the N needed for the development of the culture of corn. The hybrid BRS 3035 stands out for most of the variables analyzed, producing greater amount of dry mass of aerial part, plants with greater height, root volume and highest rates of N use efficiency. Inoculation with strain Z-94 of Herbaspirillum seropedicae promoted increase in the volume of roots, root length, dry mass of the aerial part, chlorophyll content, content of N in aboveground, absorption efficiency of N and N utilization efficiency by corn plants. Inoculation of strain Z-94 of H. seropedicae plus 80 kg ha-1 of N increased the concentration of N in the aerial part of plants of corn by as much as 25% in the evaluated genotypes. There is no distinction between maize genotypes for dry matter production of aerial part and percentage of N in aboveground from fertilizer. The P3646H and BRS3035 hybrid hybrid showed 34.3% increases and 64.4%, respectively, in the efficiency of use of Herbaspirillum seropedicae N when inoculated with no added N. Corn plants, even in fertile soil, responded to nitrogen application for the different components of production, and under such conditions, inoculation with Herbaspirillum seropedicae did not influence any of the variables studied.