Crescimento e metabolismo de nitrogênio em milho inoculado com Herbaspirillum seropedicae e Azospirillum brasilense

Abstract

In order for the corn crop to reach high yields, it is necessary a high fertility of the soil, since this grass is highly demanding in nutrients, mainly nitrogen. In order to reduce this demand for nitrogen fertilizers, some lines of research have been developed. One of the alternatives is the use of diazotrophic nitrogen-fixing bacteria. Thus, different bacteria are being used, among them, stand out Herbaspirillum seropedicae and Azospirillum brasilense. The objective of the study was to evaluate the effect of the inoculation of two diazotrophic bacteria, strain ZAE94, of Herbaspirillum seropedicae, and strain Sp245, from Azospirillum brasilense, on maize plants, on the ability to alter nitrogen growth and absorption at during the development of the crop, as well as to evaluate its productivity and yield in the weight of a thousand grains of the plants. In addition, the objective was to evaluate the effect of these bacteria on N metabolism of maize plants when grown in a hydroponic system with nutrient solution with high and low concentration of this element. For this, the thesis was divided in two chapters, where in the first one was realized two field experiments, where the first one was cultivated in the summer crop of 2015/2016 and the second one in the harvest of winter 2016. In both experiments, (Hs - Herbaspirillum seropedicae and Ab - Azospirillum brasilense), with four different replications (0 - 50, 100 and 150 kg N ha-1), with different inoculations. For the second chapter, a single greenhouse experiment was carried out using hydroponic cultivation with intermittent aeration. A factorial arrangement composed of two levels of fertilization (3.0 mM and 0.3 mM N), with different inoculations (NI - uninoculated, Hs - Herbaspirillum seropedicae and Ab - Azospirillum brasilense) was used in eight replications. It was observed that the environmental conditions influenced directly the response of the plant / bacteria interaction, where the period of higher temperature and humidity (summer harvest) promoted more expressive responses of both bacteria. Considering the plant growth and grain yield of maize plants, it was possible to show the potential of the use of diazotrophic bacteria as a biological input, mainly of the species Hesbaspirillum seropedicae, since the association of these bacteria allows the reduction of costs with fertilization, consequently, causing less environmental impact, besides promoting higher productivity and better yield and quality of maize grains. The evaluation of plant growth showed that the bacteria exerted a beneficial effect on the growth of maize plants, especially Hesbaspirillum seropedica, making them more efficient in the production of grains and in the uptake and assimilation of nitrogen by plants.