Inoculação de Azospirillum brasilense, adubação nitrogenada e ecologia molecular microbiana em sistema plantio direto

Abstract

Food security is the priority challenge of the 21st century and accompanying the growing population. Grain production must be based on increasing crop yield and not on expanding agricultural land. In this sense, adjustments on cultivation technologies are necessary to ensure better use of fertilizers, preserve soil fertility and reduce the environment's impact. Plant growth-promoting bacteria is a promising technology because it is a low cost, contributing to the cycling of essential nutrients such as nitrogen and phosphorus, protecting plants against pathogens, and increasing the development of the root and uptake water, among other advantages. The present research aimed to evaluate the impact of the application of commercial inoculants and the use of nitrogen fertilization, in a long-term no-till system, on the composition of the soil bacterial community, on the abundance of nitrogen cycle genes, and the yield of five crops (black oat, maize, wheat, soybean and rye). The results were divided into three chapters. In chapter 1 was approached the detection of Azospirillum brasilense by qPCR performed in maize inoculated seeds; the results showed that after radicle emergency, inoculated bacteria anchored in the root being detected only in roots until 75 days after sowing, in a concentration in the order of 104 CFU g-1 of fresh roots. Chapter 2 analyzed the impact of A. brasilense inoculation and three doses of nitrogen on structure and composition of the bacterial community using the partial gene sequencing of the 16S rRNA gene on the Illumina MiSeq platform. It was observed that there was no difference in the main phylum in both black oat and maize; the results confirm that no-till practices with crop rotation are fundamental for the stability of the bacterial community and fertility of agricultural soils. Finally, in chapter 3, qPCR's nitrogen gene cycle was quantified in bulk soil of black oat, maize, wheat, soybean, and rye. The abundance of gene responded differently to nitrogen fertilization and bacterial inoculation. In maize, nitrogen and bacterial inoculation decreased nifH amounts, but in wheat increased. nosZ abundance had a residual soybean effect on black oat and rye. The results confirm the importance of crop rotation under no-till for the stability of nifH and nosZ.