Azospirillum brasilense is a bacterium known for its biological nitrogen fixation (BNF) in corn crops. However, there is a lack of comprehensive research defining how much mineral N should be applied to maximize the efficiency of BNF and attain high, economically sustainable yields. Moreover, it would be interesting to investigate whether adding urea with NBPT urease inhibitor might increase BNF in grasses. Therefore, the aim of this study was to determine the effect of inoculation with Azospirillum brasilense associated with N sources and doses in a Cerrado biome soil by evaluating the grain yield of irrigated corn in economic terms. The experiment was conducted in Selvíria, MS, Brazil under a no-till system on a Latossolo Vermelho distrófico (Oxisol). The experiment was set up as a randomized block design with four replications in a 2 × 5 × 2 factorial arrangement consisting of two sources of N (urea and urea with NBPT urease enzyme inhibitor) and five N doses applied as top-dressing (0, 50, 100, 150, and 200 kg ha -1 ), with and without the inoculation of seeds with A. brasilense. Inoculation with Azospirillum brasilense makes corn growth much more profitable, irrespective of the dose and source of N. Addition of 200 kg ha -1 N in the form of conventional urea coupled with inoculation with Azospirillum brasilense increases grain yield; however, the highest economic return is obtained with N applied at 100 kg ha -1 with conventional urea and inoculation. Key words: Fertilizer with improved efficiency. Nitrogen fertilization. No-tillage system. Total operational cost. Urea. Zea mays.
ResumoO Azospirillum brasilense se destaca na fixação biológica de nitrogênio (FBN) em cultivo de milho. Contudo, faltam maiores pesquisas para definição do quanto se pode aplicar de N mineral quanto à eficiência da FBN, para alcançar altas produtividades economicamente sustentáveis. Além disso, seria interessante analisar se a ureia com inibidor da enzima urease NBPT pode ser menos prejudicial, beneficiando a FBN em gramíneas. Sendo assim, objetivou-se estudar o efeito da inoculação com Azospirillum brasilense, associado às doses e fontes de N, em solo de Cerrado, avaliando economicamente a produtividade de grãos de milho irrigado. O experimento foi desenvolvido em Selvíria -MS, em sistema plantio direto, em Latossolo Vermelho distrófico. O delineamento experimental foi em blocos