Ureia revestida e aplicação foliar de Azospirillum brasilense no capim marandu

Abstract

The pasture environment cultivated with tropical forages requires the addition of nitrogen, as this nutrient increases the crude protein content in the forage available to the animals. And as nitrogen has loss pathways such as volatilization and/or leaching, its absorption, maintenance or permanence in this environment is possible with the association of microorganisms with mineral fertilization. Thus, the objective was to evaluate the association between the bacterium Azospirillum brasilense and urea use strategies on morphological characteristics, nutrient accumulation, bromatological composition, efficiency and recovery of N applied to Marandu grass. To this end, a field experiment was installed in the Amazon biome in an experimental design in randomized blocks in a 2x3 factorial scheme, with treatments coming from the association of with and without A. brasilense and two sources of nitrogen (common urea; coated urea) and a fertilizer factor level without nitrogen application with four replications. At each growth cycle, 40 kg of N ha−1 and a dose of 300mL ha−1 of Azospirillum brasilense foliar inoculant were applied. The variables evaluated were: accumulated shoot dry mass production (ASM), accumulated leaf blade production (LB), increase in accumulated height (IA), tiller population density (PD), accumulation of N, P, K, Ca, Mg, S of the aerial part (ANAP), bromatological composition [contents of crude protein (CP), mineral matter (MM), neutral detergent fiber (NDF), acid detergent fiber (ADF), indigestible neutral detergent fiber (iNDF)], the nitrogen-use efficiency (NUE) and nitrogen recovery from Marandu grass (NRA). Leaf inoculation of A. brasilense associated with nitrogen fertilization promotes improvements in morphological characteristics such as increased AMS, LB and IA, and higher NUE in the Amazon environment. Inoculation with A. brasilense promoted greater Ca accumulation in the aerial part of plants fertilized with urea. Regarding sources, coated urea promotes an increase in AMS, LB, IA and the absorption of N, Ca and Mg, and decreased the iNDF of Marandu grass compared to the treatment common urea. Regardless of the inoculation, Marandu grass fertilized with coated urea recovered more N and had higher NUE when compared to common urea. It is concluded that the association of A. brasilense and coated urea showed synergism, therefore, it becomes an essential and promising tool in established pasture, as it promotes increases in morphological characteristics, accumulation of macronutrients, NUE and increases in production of CP ha−1.