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The use of living mulch with legumes is increasing but the impact of this management technique on the soil microbial pool is not well known. In this work, the effect of different live mulches was evaluated in relation to the C, N and P pools of the microbial biomass, in a Typic Alfisol of Seropédica, RJ, Brazil. The field experiment was divided in two parts: the first, consisted of treatments set in a 2 x 2 x 4 factorial combination of the following factors: live mulch species (Arachis pintoi and Macroptilium atropurpureum), vegetation management after cutting (leaving residue as a mulch or residue remotion from the plots) and four soil depths. The second part had treatments set in a 4 x 2 x 2 factorial combination of the following factors: absence of live mulch, A. pintoi, Pueraria phaseoloides, and M. atropurpureum, P levels (0 and 88 kg ha -1) and vegetation management after cutting. Variation of microbial C was not observed in relation to soil depth. However, the amount of microbial P and N, water soluble C, available C, and mineralizable C decreased with soil depth. Among the tested legumes, Arachis pintoi promoted an increase of microbial C and available C content of the soil, when compared to the other legume species ( Pueraria phaseoloides and Macroptilium atropurpureum ). Keeping the shoot as a mulch promoted an increase on soil content of microbial C and N, total organic C and N, and organic C fractions, indicating the importance of this practice to improve soil fertility. ) e manejo dos resíduos da parte aérea das plantas. Não houve variação do C microbiano com a profundidade do solo. Porém, para o P e N microbianos, C orgânico do solo, C solúvel em água, disponível e mineralizável, o aumento da profundidade proporcionou diminuição destas características. As leguminosas usadas influenciaram de maneira diferenciada as variáveis analisadas. O A. pintoi promoveu elevação nos teores de C microbiano e disponível, comparativamente as demais espécies utilizadas ( P. phaseoloides e M. atropurpureum). A manutenção dos resíduos das leguminosas após cada corte promoveu aumentos nos teores de C e N microbianos, C orgânico e N total e frações de C orgânico do solo enfatizando a importância de utilização desta prática para melhorar a fertilidade do solo. Palavras-chave: fósforo microbiano, adubo verde, ciclagem de nutrientes

-An experiment was carried out under field conditions to assess the effects of soil management (no-tillage-NT and conventional tillage-CT) and crop rotation systems on microbial biomass-C (C mic ), basal soil respiration (BSR), metabolic quotient (qCO 2 ), soil organic carbon content (C org ) and microbial carbon to organic carbon ratio (C mic /C org ). Soil samples were collected on an area cultivated with wheat as winter crop and soybean as summer crop, both in rotation with vetch, maize and oats. Samples were also collected in a secondary forest used as reference. Data of each management system (NT and CT) were compared to forest area by "t" test (p<0.05) and crop rotations were compared by Tukey test (p<0.05). All data were submitted to multivariate analysis (Principal Component Analysis -PCA). There were observed significant differences ("t" test; p<0.05) for C mic , BSR, qCO 2 and C mic /C org between NT and CT, by which NT values resemble those for forest area. For crop rotations significant differences (Tukey test; p<0.05) were found only for BSR and qCO 2 . The sum of the two first principal components on the PCA explained about 75% of the data variation. PCA showed NT closest to forest area than CT, especially treatments with soybean and vetch as consecutive crops. The forest area-NT clustering was mostly due to C mic and C mic /C org relationship. Results indicate that the NT system is more sustainable than the CT system and can contribute for the accumulation a greater quantity of carbon in soil.Key words -Microbial biomass. Microbial respiration. Organic matter. Soil management.Resumo -Foi conduzido um experimento sob condições de campo para avaliar o efeito da forma de manejo do solo (Plantio direto -PD e plantio convencional -PC) e dos sistemas de rotação de culturas sobre o carbono da biomassa microbiana (C mic ), respiração basal do solo (RBS), quociente metabólico (qCO 2 ), carbono orgânico total (C org ) e relação carbono da biomassa microbiana: carbono orgânico total (C mic /C org ). As amostras de solo foram coletadas em uma área cultivada com trigo como cultura de inverno e soja como cultura de verão, ambas em rotação com ervilhaca, milho e aveia preta. Amostras de solo também foram coletadas em uma floresta secundária usada com referência. Os dados de cada sistema de manejo do solo (PD e PC) foram comparados com a floresta secundária pelo teste "t" (p<0.05) e as rotações de culturas foram comparadas pelo teste de Tukey (p<0.05). Todos os dados foram submetidos a uma análise multivariada (Análise de Componentes Principais -ACP). Foram observadas diferenças significativas (teste "t"; p<0.05) para C mic , RBS, qCO 2 e C mic /C org entre PD e PC, em que estes valores foram semelhantes àqueles encontrados na floresta. Entre as rotações de culturas foram observadas diferenças significativas (teste de Tukey; p<0.05) apenas para RBS e qCO 2 . A análise de componentes principais mostrou que o PD aproximou-se mais da floresta do que o PC, especialmente nos tratamentos em que soja e ervilhac...

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