RESUMO. Objetivou-se estudar a viabilidade de uma pastagem com alta capacidade produtiva e o potencial para produção de silagem de capim, utilizando fontes e doses de nitrogênio (N), quantificando-se a produtividade de matéria seca (PMS), algumas características bromatológicas, o custo total de produção (CT) e o custo operacional total (COT) da produção de silagem. O delineamento experimental foi em blocos casualizados, adotando um esquema fatorial com quatro repetições, sendo duas fontes de nitrogênio: ureia, e nitrato de amônio, e cinco doses de N (0, 50, 100, 150 e 200 kg ha-1 por corte). O incremento de N propiciou maior PMS e teor de proteína bruta, além de diminuir os teores de fibra em detergente neutro. As fontes de N, não influenciaram na composição química, e desta forma recomenda-se utilizar a ureia em função da facilidade de aquisição e maior retorno econômico. A produção de silagem de capim-Mombaça pode ser economicamente viável em função da elevada PMS e proteína bruta, aliado ao baixo custo de produção. O menor CT e COT foi obtido na ausência da adubação nitrogenada, entretanto, o manejo adequado de N garante boa produtividade e rendimento na alimentação do rebanho, com maior lucro total obtido na utilização de 100 kg ha-1 de N por corte com a fonte nitrato de amônio.

ABSTRACT. The objective of this study was to evaluate the viability of pasture with high production capacity and the potential for production of silage using different sources and doses of nitrogen (N) by quantifying the productivity of dry matter (DM), some qualitative characteristics, the total cost of production (TC) and total operating cost (TOC) of silage production. The experimental design was randomized block in a factorial scheme with four replications including two sources of nitrogen (urea and ammonium nitrate) and five N doses (0, 50, 100, 150, and 200 kg ha-1 by cutting). The increase in N provided greater DM and crude protein content and reduced the fiber content in neutral detergent. The source of N did not affect the chemical composition, and therefore, it is recommended to use urea due to the ease of acquisition and higher economic return. The production of Mombasa silage can be economically viable due to high DM and crude protein content combined with low production costs. The smallest TC and TOC were obtained in the absence of nitrogen fertilization; however, the proper management of N ensures high productivity in cattle feed with higher total profit when using 100 kg ha-1 N by cutting with ammonium nitrate.

Resumo: O objetivo deste trabalho foi avaliar o efeito da inoculação com Azospirillum brasilense, associada a doses e fontes de N, em solo de Cerrado, sobre a produtividade de grãos de trigo (Triticum aestivum) irrigado. O experimento foi desenvolvido em sistema plantio direto, em Latossolo Vermelho distrófico. Utilizou-se o delineamento experimental de blocos ao acaso, com quatro repetições, em arranjo fatorial 2x5x2: duas fontes de N (ureia e ureia com inibidor da urease NBPT); cinco doses de N em cobertura (0, 50, 100, 150 e 200 kg ha-1); e com ou sem inoculação das sementes com A.brasilense. O aumento nas doses de N apresentou efeito positivo no comprimento de espiga, número de espiguetas e de grãos por espiga, número de espigas por metro, acúmulo de N na palha, conteúdo de clorofila na folha e produtividade de grãos de trigo irrigado, independentemente do uso de inibidor de urease NBPT com ureia. Isoladamente, a inoculação com A.brasilense não afeta os componentes de produção e a produtividade de grãos, apesar de incrementar o N na palhada de trigo. A inoculação com A.brasilense, associada à aplicação de 140 kg ha-1 de N, propicia as maiores produtividades de grãos de trigo irrigado, cultivado após milho em Cerrado de baixa altitude.

Abstract: The objective of this work was to evaluate the effect of inoculation with Azospirillum brasilense, associated with N rates and sources, in soil of the Cerrado (Brazilian savanna), on the grain yield of irrigated wheat (Triticum aestivum). The experiment was carried out under a no-tillage system in a Typic Haplustox. The experimental design was randomized complete blocks with four replicates, in a 2x5x2 factorial arrangement: two N sources (urea and urea with NBPT urease inhibitor); five N rates applied as topdressing (0, 50, 100, 150, and 200 kg ha-1); and with or without seed inoculation with A.brasilense. The increase in the N rates positively affected spike length, number of spikelets and of grains per spike, number of spikes per meter, N accumulation in the straw, leaf chlorophyll content, and grain yield of irrigated wheat, regardless of the use of NBPT urease inhibitor with conventional urea. Singly, inoculation with A.brasilense does not affect production components and grain yield, despite the increase in N content in wheat straw. The inoculation with A.brasilense, associated with the application of 140 kg ha-1 N, provides the highest grain yield of irrigated wheat cropped after corn in low-altitude Cerrado.

ABSTRACT The biological nitrogen fixation (BNF) process in grasses is caused by diazotrophic bacteria, particularly Azospirillum brasilense. However, studies are lacking on BNF efficiency to define how much mineral nitrogen (N) can be applied to achieve more sustainable high yields. Furthermore, there should be an analysis of whether urea with the urease enzyme inhibitor NBPT is less harmful, benefiting BNF in grasses. The objective of this study was to evaluate the effect of N sources and N rates associated with inoculation with Azospirillum brasilense regarding foliar diagnosis and leaf chlorophyll index (LCI), agronomic efficiency (AE), and corn grain yield in the Cerrado (Brazilian tropical savanna) region. The experiment was conducted in a no-tillage system in a Latossolo Vermelho Distroférrico (Oxisol). A randomized block experimental design was used with four replications in a 2 × 5 × 2 factorial arrangement as follows: two N sources - urea and Super N, urea with urease enzyme inhibitor NBPT [N - (n-butyl thiophosphoric triamide)]; five N rates (0, 50, 100, 150, and 200 kg ha-1) applied in topdressing; and two seed inoculation treatments, one with and one without A. brasilense. N rate positively influenced the LCI and concentrations of N, S, and Mn in leaves, and may increase the concentrations of P, Cu, and Fe; however, higher N rates can reduce AE. The N sources had similar effects, and therefore urea is recommended for N fertilization. Inoculation with A. brasilense decreased leaf concentration of Fe and increased LCI, leaf concentration of P, AE, and corn grain yield; the use of this diazotrophic bacterium is therefore viable even when high rates of N are applied.