ABSTRACT The implementation of integrated agricultural production systems is considered a promising strategy for sustainable agricultural intensification in Brazil. This study aimed to evaluate the effects of different monoculture and integrated production systems on the microbiological attributes and organic carbon of soil from the Cerrado region in Piauí, Brazil. Soil samples were collected from the 0.0-0.10-m layer in the following systems: no-tillage (PD), pasture (PAS), exclusive eucalyptus cultivation (CEE), integrated livestock-forest system (IPF) and a native Cerrado (CN) area, which was used as reference. Total organic carbon (TOC) and nitrogen (NT) contents, microbial biomass carbon (CMIC), microbial respiration (MR), microbial quotient (qMIC), metabolic quotient (qCO2), as well as the activities of the hydrolysis of fluorescein diacetate (FDA), acid phosphatase, β-glucosidase and urease enzymes were evaluated. High TOC contents were found in the CEE, IPF and PAS systems, and high CMIC and qMIC values were found in the CN and CEE systems. The variables MR, qCO2 and enzymatic activity varied as a function of the management systems. The IPF and CEE systems caused improvements in the soil attributes, with increases in organic carbon and microbial biomass. The IPF integrated production system promoted improvements in the microbiological indicators of soil quality and was considered an environmentally sustainable agricultural production system. The transition from CN to agricultural areas caused changes in the soil microbiological indicators, which were perceived several years after anthropogenic intervention, indicating that even with the adoption of conservation systems, it was not possible to reestablish the soil microbial biomass.

ABSTRACT The substitution of native vegetation by agricultural ecosystems can change the quantity and quality of soil organic matter (SOM), and the intensity of these changes depends on the soil type, climate, and land use. The objective of this study was to evaluate the quality of organic matter in chronosequences of Jatropha cultivation in contrasting soil and climatic conditions. Soil samples were evaluated at depths of 0.00-0.10, 0.20-0.30, and 0.80-1.00 m in chronosequences located in Planaltina, Distrito Federal (Cerrado-Pasture-Jatropha), Dourados, Mato Grosso do Sul (Atlantic Forest-Corn-Jatropha), and Araripina, Pernambuco (Caatinga-Jatropha). To assess SOM quality, we determined C contents in the SOM fractions, C stocks, the carbon management index (CMI), the SOM humification index (HLIF), and the C and N concentrations in the microbial biomass. The conversion of native vegetation to agropastoral systems changed the composition of SOM in the biomes evaluated, especially in the surface layers. The CMI and the C and N contents in the microbial biomass were the most responsive to land use changes in all the biomes studied. The pasture improved SOM quality by increasing the CMI (116) and the C content by 8, 21, and 6 % in the organic, mineral, and organomineral fractions, respectively, while maintaining the SOM humification index and the C and N contents in the microbial biomass in the 0-0.10 m layer. The lowest values of C in the SOM fractions, the CMI (52), and C microbial biomass (136 mg kg-1) were observed for annual crops. Jatropha cultivation increased C contents in the SOM fractions, C stocks, the CMI, and C and N in the microbial biomass with an increase in cultivation time, which demonstrates the potential of this long-term system for improving SOM quality.

Resumo No sistema plantio direto, o uso de plantas de cobertura é uma alternativa amplamente utilizada para aumentar a sustentabilidade do sistema agrícola. O objetivo deste trabalho foi avaliar a decomposição e liberação de nitrogênio (N), fósforo (P) e potássio (K) totais por resíduos culturais, provenientes do pousio e de culturas de cobertura (milheto e braquiária) solteiras e consorciadas, em Latossolo Amarelo no Cerrado Maranhense. O experimento foi conduzido em área sob plantio direto, após a colheita da cultura do milho, onde foram avaliadas a produção de fitomassa seca, decomposição dos resíduos em bolsas de polietileno (litterbags) e liberação de nutrientes (N, P e K), a cada 20 dias, até 100 dias após a dessecação. A braquiária e o milheto solteiros ou consorciados e a vegetação espontânea apresentaram decréscimos semelhantes na decomposição da matéria seca remanescente (MSR) nos primeiros 60 dias, com perdas de 10; 13; 16 e 12%, respectivamente. A maior e a menor taxa de liberação de N ocorreram no consórcio milheto + braquiária e no milheto, respectivamente. O K foi o nutriente liberado mais rapidamente do resíduo vegetal para o solo durante o processo de mineralização, em todos os tratamentos. A braquiária é a cobertura com maior resistência à decomposição, mantendo o resíduo sobre o solo por maior período de tempo em áreas do cerrado maranhense.

Abstract In the no-tillage system the use of cover crops is a widely adopted alternative to increase the sustainability of the agricultural system. This study aimed to evaluate the decomposition rate and total nitrogen (N), phosphorus (P) and potassium (K) release from the biomass of natural bush fallow and cover crops (Brachiaria sp., millet and Brachiaria sp. + millet intercrop), cultivated on a Yellow Latosol in the savanna of the Maranhão State. The experiment was carried out under no-tillage system after maize harvesting. Dry matter production, decomposition rate and nutrient release (N, P and K) at twenty-day intervals, until one hundred days after biomass cutting were evaluated. Millet or Brachiaria sp. mono or intercropped and natural bush fallow showed similar decreases in their decomposition in the first sixty days, with losses of 10; 13; 16 e 12% respectively. The highest and lowest rate of N release was observed on millet and Brachiaria sp. + millet intercrop, respectively. Among the nutrients, K was the earliest released in all treatments. The Braquiaria sp. is the cover crop with greater resistance to decompose, keeping the residue on the soil for longer periods in the Cerrado of Maranhão State.

Os estoques totais de carbono orgânico (C) e nitrogênio (N) e a produção de culturas são influenciados pelo preparo do solo, pelo aporte de resíduos e pela fertilização nitrogenada. Este trabalho teve como objetivo avaliar o efeito de diferentes sistemas de preparo associados às doses de nitrogênio sobre a produtividade do milho e os estoques de C e N de um Latossolo Vermelho-Amarelo no cerrado piauiense. O experimento foi realizado no Município de Baixa Grande do Ribeiro, sudeste do Estado do Piauí. O delineamento experimental foi em blocos ao acaso, em esquema fatorial 2 x 5, (dois sistemas de preparo: (plantio direto (PD) e convencional (PC) e; cinco doses de nitrogênio (0, 60, 120, 180 e 240kg N ha-1)), com seis repetições. Foram avaliados a produtividade de grãos (PG), os aportes de C e N, provenientes da cultura do milho, e os estoques de C e N no solo, nas camadas de 0-5, 5-10, 10-20 e 20-40cm. As doses de N ocasionaram resposta quadrática na produtividade de grãos e no aporte e estoque de C e N, tanto no PC, quanto no PD. As maiores produtividades de grãos foram obtidas com as doses de 138 e 134kg N ha-1 para PC e PD, respectivamente. Os maiores aportes de C e N no PC foram observados nas doses de 140 e 175kg ha-1 de N e no PD, nas doses de 139 e 100kg ha-1 de N, respectivamente. A adubação nitrogenada aumentou os estoques de C no solo, no sistema PD, em comparação ao PC, nas camadas de 0-5 e 5-10cm. A adoção do sistema plantio direto em combinação com aplicação balanceada de fertilizante nitrogenado é importante para construção da matéria orgânica em solos do cerrado piauiense.

Total soil organic carbon (C) and nitrogen (N) stocks and crop yield are influenced by tillage, biomass input from crop and nitrogen fertilization. This research aimed to evaluate the effect of different tillage systems associated to nitrogen doses on corn yield and C and N stocks in the Red Yellow Latosol in savanna of Piauí state, Brazil. The experiment was carried out in Baixa Grande do Ribeiro, south of Piauí state. The treatments were distributed in a randomized complete blocks and factor arrange 2x5, two tillage systems (no-tillage (NT) and conventional (CT)) and five nitrogen doses (0, 60, 120,180 and 240kg ha-1 N), respectively, with six replications. The corn grain yield (GY) and C and N inputs were measured and C and N soil stocks were evaluated in the 0-5, 5-10, 10-20 and 20-40cm. N doses caused a quadratic response in the grain yield, C and N inputs from maize crop and soil C stocks in both tillage systems. Higher GY were obtained by 138 and 134kg N ha-1 to CT and NT, respectively. Higher C and N inputs were obtained by 140 and 175kg N ha-1, in the CT and by 139 and 100kg N ha-1 in the NT system, respectively. Nitrogen fertilization increased soil C stocks in the NT comparing to CT in the 0-5 and 5-10 depths. No tillage adoption combined with balanced nitrogen fertilization can be important to soil organic matter production in soils under cerrado of Piauí state.