Resumo -O objetivo deste trabalho foi avaliar o efeito da adubação nitrogenada no nitrogênio da biomassa microbiana do solo (N BMS ), em diferentes profundidades, em um Latossolo Vermelho-Amarelo cultivado com cevada. O experimento foi instalado em junho de 2004, em área experimental de primeiro ano de plantio direto, anteriormente cultivada com milheto por três anos e posteriormente com soja por duas safras. Foram utilizados os seguintes tratamentos: quatro doses de nitrogênio (30, 60, 90 e 120 kg ha
Microbial biomass nitrogen in cerrado soil with nitrogen fertilizer applicationAbstract -The objective of this work was to evaluate the effect of different nitrogen doses and soil depths on soil microbial biomass nitrogen (N SMB ) in a sandy textured Oxisol, cultivated with barley. The experiment was established in June, 2004, in an area which had been cultivated with millet for three years and subsequently with soya beans for two seasons. The treatments were four doses of nitrogen (30, 60, 90 e 120 kg ha -1 ) and a control without any dose. Soil samples were collected in four depths: 0-5, 5-10, 10-20 e 20-30 cm, comprising three replicates and three sampling periods: tillering, flowering and right after the harvest. The N SMB and N SMB :N total decreased according to depth. Higher doses of nitrogen did not increase the N SMB . The N total was not altered with the application of nitrogen, but it decreased with depth. There were negative correlations between the N SMB and soil pH for all the doses, except for the treatment without nitrogen. There were also positive correlations between the N SMB :N total and N SMB , but not between N SMB :N total and N total .