The objective of this work was to study the effect of grazing systems: rotational, continuous and the absence of cattle, in pastures of Brachiaria brizantha on microbial activity (respiratory, potential nitrification, solubilizing, and enzymatic) and on the chemical attributes (contents of organic carbon, total nitrogen, organic phosphorus, and moisture) of Eutrustox soil over one year. Eight Canchim breed animals were used. The samples were collected in the four seasons from 2005 to 2006. The average of organic C, organic P, and moisture contents, as well as potential nitrification and solubilizing activity and urease and acid phosphatase activities were significantly higher in the spring and/or summer than in autumn and/or winter. The total nitrogen amounts did not vary among seasons. While the respiratory activity was larger during winter and summer, cellulase activity was smaller during spring than in the other seasons. Except for organic P, higher values of the variables studied were observed in the rotational grazing. The results indicate that the hot and rainy season and the rotational grazing system cause increases in the soil microbiological and chemical attributes.

Os efeitos da lotação de animais na produção de ovinos têm sido bastante estudados. No entanto, informações sobre seus efeitos na biomassa e nas atividades microbianas e, em conseqüência, na fertilidade do solo de pastagens são escassas. Neste trabalho, os efeitos da lotação de ovinos (LO) na biomassa e nas atividades microbianas responsáveis pela transformação dos compostos do C e N em solo de clima subtropical foram avaliados. As amostras de solo foram coletadas nas camadas de 0-10 e 10-20 cm de pastos com baixa LO (5 animais ha-1), alta LO (40-50 animais ha-1) e com ausência de animais, em um delineamento inteiramente casualizado em parcelas subdivididas, com seis repetições. Os maiores valores de biomassa microbiana e das atividades respiratória, nitrificante e enzimática (urease e protease) foram encontrados nos solos dos pastos com baixa LO. Estes pastos também acumularam as maiores quantidades de matéria orgânica e N total. Essas variáveis foram reduzidas nos pastos sem animais ou com alta LO. Vegetação descontínua e intensa mineralização podem ter acarretado a diminuição dessas variáveis nos pastos com alta LO. Alta correlação foi obtida entre matéria orgânica, C orgânico e N total com as quantidades de biomassa microbiana e a atividade enzimática. A camada de 0-10 cm apresentou valores maiores das variáveis estudadas do que os encontrados na camada de 10-20 cm.

The effect of grazing pressure in sheep production has been studied, but not in relation to soil microbiological parameters or the consequences on soil fertility. The effect of grazing pressure (GP) by sheep on biomass and microbial activity related to C and N compounds cycling in subtropical region soil was studied. Soil samples were collected from the 0-10 cm and 10-20 cm layers in pastures with low GP (5 animals ha-1), high GP (40-50 animals ha-1) and in absence of animals, in a completely randomized design with 6 replicates. The highest values of microbial biomass and respiratory, nitrifying and enzymatic (urease and protease) activities were found in pasture soil with low GP. This pasture also accumulated highest amounts of organic matter and total N. These variables decreased in pastures without animals or with high GP. Discontinuous vegetation and intense mineralization may have caused this reduction in the soils with pastures under high GP. It was observed a high correlation between organic matter, organic C and total N with the amounts of microbial biomass and enzymatic activity. The values of the variables under study were higher in the 0-10 cm than in the 10-20 cm layer.

O objetivo deste trabalho foi quantificar variáveis microbiológicas e produtividade do feijoeiro em razão do manejo do solo e da calagem. Parte de uma área cultivada há 20 anos em plantio direto (PD) foi submetida ao cultivo mínimo (CM), com escarificação a 0,25 m de profundidade, para incorporação do calcário. Os tratamentos consistiram de manejo do solo (PD e CM) e 0 e 2 t ha-1 de calcário dolomítico aplicadas na superfície, com quatro repetições. Os maiores valores de C da biomassa microbiana foram verificados no CM e os de C de CO2 liberado no PD sem calagem. A menor colonização micorrízica e a maior esporulação foram observadas no CM sem calagem. Não foram detectadas diferenças entre os tratamentos em relação à produção de matéria seca, enquanto na produtividade de grãos, o maior valor foi verificado no CM com calagem. É possível evitar a interrupção do PD com aplicação de calcário na superfície, visto que a incorporação do material de cobertura e a calagem pouco alteraram a estabilidade do sistema, conforme comprovado pelos valores estatísticos semelhantes de C do CO2 liberado e pelas pequenas diferenças observadas nas demais variáveis entre manejos.

The objective of this study was to quantify the microbial variables and the productivity of bean under different soil managements and limestone application. Part of a site under no-tillage (NT) system for 20 years was submitted to minimum tillage (MT), with limestone incorporation at 0.25 m depth and chisel plowing. The treatments were soil managements (NT and MT) and surface limestone application (0 and 2 t ha-1), with four replicates. Carbon of microbial biomass higher values were found on the MT and CO2 evoluted, on the NT without limestone application. The smallest mycorrhizal colonization and the highest number of spores were observed on the MT without limestone application. No significant differences among treatments were detected for dry matter production. For grain yield, the higher values were found on the MT with limestone application. It is possible to avoid interruptions on the NT by the surface application of limestone, once the incorporation of organic material and limestone induced little changes on the system stability, which was confirmed by the similarity among statistical values for the C-CO2 evoluted and the slight differences for the other variables studied between soil managements.