ResumoO objetivo deste trabalho foi avaliar o potencial de plantas de cobertura semeadas em diferentes sistemas de cultivo quanto à produção de fitomassa e acúmulo de nutrientes, no cerrado piauiense. O experimento foi instalado no ano agrícola 2010/2011, na Serra do Quilombo, município de Bom Jesus (Piauí). O arranjo utilizado foi em parcelas subdivididas, com os seguintes sistemas de manejo do solo: preparo convencional e plantio direto avaliados nas parcelas e, nas subparcelas, os sistemas de produção: S 1 -Soja no verão em monocultura; S 2 -Soja no verão e Penissetum glaucum na safrinha; S 3 -P. glaucum pré-soja de verão e sobressemeadura de Urochloa ruziziensis na soja no estádio R 5.5 ; S 4 -Soja de verão e sobressemeadura de P. glaucum na soja no estádio R 5.5 ; S 5 -Milho verão + U. ruziziensis simultâneo. Utilizou-se o delineamento em blocos casualizados, com quatro repetições. Os sistemas com a sobressemeadura do P. glaucum e do U. ruziziensis na soja e o consórcio de milho + U. ruziziensis destacaram-se na produção de fitomassa seca, cobertura do solo e acúmulo de nutrientes durante a entressafra no cerrado piauiense. Os nutrientes com maior taxa de acúmulo pelas plantas de cobertura foram o nitrogênio e o potássio.Palavras-chave: Braquiária, milheto, decomposição, crotalária, plantio direto. Biomass production and nutrient accumulation by cover crops in the Brazilian Cerrado of Piauí State AbstractThe objective of this work was to evaluate the biomass production and nutrient accumulation in potential cover crops sown in different cropping systems in the Brazilian Cerrado of Piauí State. The experiment was conducted in the crop season 2010/2011 in the Serra do Quilombo, county of Bom Jesus, Piauí, Brazil. This study was arranged in split plot scheme, with soil management systems (conventional tillage and no-tillage) evaluated in plots and crop systems in subplots: S 1 -Soybean monoculture in the crop-season; S 2 -Soybean in crop-season and Pennisetum glaucum for off-season; S 3 -P. glaucum before soybean crop-season and Urochloa ruziziensis oversown on soybean in the phenological stage R 5.5 ; S 4 -Soybean crop-season and P. glaucum oversown on soybean in R 5.5 ; S 5 -Maize + U. ruziziensis simultaneously in crop-season. The experimental design was in randomized blocks, with four replications. The crop systems with oversown of P. glaucum and U. ruziziensis on soybean and the consortium maize + U. ruziziensis improved the biomass production, soil coverage and nutrient accumulation during the off-season in the Cerrado from Piauí State, Brazil. The nutrients with greater accumulation rate by cover crops were nitrogen and potassium.

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The Cerrado biome has outstanding territorial relevance in the state of Piauí, in which weather conditions, relief and favorable soil has made this region one reference in food production. This study focused to evaluate the effects of different land uses, management systems and their respective terms on organic carbon content and physical properties of a Latossolo Amarelo (Oxisol) in the Southwestern Piauí state. The study was performed in the city of Uruçuí, situated in the southwestern Piauí state. We assessed nine farming areas with different backgrounds regarding land-use, management system and run time. The treatments consisted of areas under no-till for 3 and 6 years (NT3 and NT6), under pasture for 2 and 5 years (PA2 and PA6), under eucalyptus plantation for six and twelve years (EU6 and EU12), under conventional tillage for two and 8 years (CT2 and CT8) and under native Cerrado (NC), which represented a reference condition. Conversion of the native Cerrado into no-till and grazing areas increased soil organic carbon content over time.

Sandspur grass has hindered the integrated weed management in the Brazilian crop systems. This study aimed at evaluating the efficiency of biomass levels of different cover crops on the soil surface to control the sandspur grass. A complete randomized blocks design with four replications, in a 6 x 5 + 1 factorial arrangement, was used. The first factor consisted of six cover crops (Pennisetum glaucum-ADR 7010 and ADR 300 cultivars, Crotalaria ochroleuca, Urochloa ruziziensis, Fagopyrum tataricum and Crambe abyssinica) and the second one consisted of five biomass levels of each species (2 t ha-1, 4 t ha-1, 8 t ha-1, 12 t ha-1 and 16 t ha-1), plus a control treatment without soil cover. The variables analyzed were the total number of emerged plants, germination speed index, leaf area, root volume and shoot and root dry biomass. U. ruziziensis excelled in the suppression of C. echinatus growth by reducing the number of emerged plants, emergence speed index, shoot and root dry biomass, root volume and leaf area.

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The Cerrado biome is of notable territorial relevance in the state of Piaui, Brazil. This region is an area of reference for food production. The aim of this work was to evaluate the stability of soil aggregates in water, in function of different soil use and management systems, as well as of the time since adopting these systems in Cerrado areas in the southwest region of Piaui. In this study, nine soil use and management systems were evaluated, arranged in the following manner: no-tillage system of three and six years of use, pasture of two and six years, eucalypt of six and twelve years, conventional tillage of two and eight years, and native Cerrado (Savana). The analyzed variables were: organic carbon, mean geometric diameter, mean weight diameter, aggregate stability index and aggregate diameter classes. Aggregation in Ferralsol is favored by clay and organic carbon contents. The longer adoption time in the no-till, pasture and eucalypt systems favored soil aggregation, while in conventional tillage there was a reduction of the aggregates.

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