Abstract The Cerrado/Caatinga transition region in Piauí State has a high potential for production of food, fiber and energy, representing about 19% of the total area of the State. This work aimed to evaluate physical and hydraulic attributes under different crops in Latossolo Amarelo Distrófico (Oxisol) in cerrado/caatinga transition areas, in the Southwest of Piauí. In this study five areas with different crops were evaluated as follows: areas under pasture crop with Andropogon gayanus grass with three and six years of crop, area under intensive crop of Pennisetum purpureum grass, area under orchard of Annona squamosa L., area under intensive crop irrigated with central pivot and area under native vegetation of cerrado/caatinga ecotone representing a condition of equilibrium. Soil attributes evaluated were: soil density, total porosity, macroporosity, microporosity, unsaturated pores, blocked pores, saturation humidity, effective saturation, water readily available, void index, mechanical resistance of soil and saturated field hydraulic conductivity. The intensive crop of napier grass for five consecutive years and the pivot irrigated area under intensive crop for four years presented the greatest negative impacts on soil density, total porosity, macroporosity, saturation humidity, effective saturation, water readily available and index of voids.

Abstract Soil quality is essential for maintaining the sustainability of agro-ecosystems and ecosystem services provided by this natural resource. The present study aimed to assess the physical quality of soil through the characterization of the physical properties in grain production systems in the Southwest region of Piauí State, Brazil. The study was carried out in the Cerrado region of Piauí in four cities in areas of expansion of the agricultural frontier of the state: Baixa Grande do Ribeiro, Sebastião Leal, Uruçuí and Bom Jesus. Soil samples were collected in April 2012, in areas of grain production under conventional and no-tillage systems. Adjacent areas with native vegetation were also sampled as reference. Bulk density, effective saturation, hydraulic conductivity, penetration resistance, porosity and aggregation were measured. Regardless of the type of soil management used, agricultural systems degrade soil physical quality. No-tillage showed higher bulk density, penetration resistance and aggregation, with lower total porosity, macroporosity and hydraulic conductivity. The physical quality of soil in the agricultural areas of the Cerrado region of Piauí was dependent on the soil texture, while silt, clay and organic matter were determinant for soil aggregation, mechanical resistance, total porosity and microporosity.

A fixação biológica de azoto é uma importante alternativa para o fornecimento de azoto (N) às leguminosas. O presente trabalho objetivou avaliar a qualidade de mudas de Enterolobium contortisiliquum (Vell.) Morong em função da inoculação e da nodulação natural em solos do Sudoeste do Piauí. O delineamento experimental foi inteiramente casualizado, com cinco repetições, e os tratamentos arranjados em esquema fatorial (5 x 4), constituídos por cinco classes de solo e quatro tratamentos de N (a-inoculação com a estirpe BR 4406, b-adubação com N mineral, c-adubação com N mineral e inoculação com a estirpe BR 4406, d-sem N mineral e sem inoculação). Aos 75 dias após a semeadura foram avaliados: nodulação, eficiência da fixação de N2, acúmulo de azoto na massa seca da parte aérea e parâmetros morfológicos das mudas. As mudas de E. contortisiliquum apresentaram nodulação natural apenas quando cultivadas no Organossolo e Neossolo Flúvico. A estirpe inoculante BR 4406 mostrou-se pouco adaptada aos solos do Sudoeste piauiense constituintes dos substratos de cultivo. As mudas cultivadas no Neossolo Quartzarênico, Organossolo e Neossolo Flúvico apresentam melhor qualidade em relação às cultivadas no Latossolo Amarelo e Neossolo Litólico.

Biological nitrogen fixation is an important alternative to provide nitrogen (N) to legumes. This study aimed to evaluate the quality of Enterolobium contortisiliquum (Vell.) Morong seedlings depending on the inoculation and natural nodulation in soils from southwest of Piauí, Brazil. The experimental design was completely randomized with five replications and treatments arranged in a (5 x 4) factorial design, consisting of five soil classes and four N treatments (a-inoculation with strain BR 4406, b- with application of mineral N, c- with mineral N and inoculation with BR 4406, d- without mineral N or inoculation). Seventy five days after sowing number and fresh weight of nodules, N2 fixation efficiency, nitrogen concentration in shoot and morphological parameters of seedlings were evaluated. The seedlings of E. contortisiliquum presented natural nodulation only when grown on Organosol and Fluvic Neossol. The inoculant strain BR 4406 showed a very low adaptation to the soils from Southwest of Piauí. Seedlings grown in Quartzarenic Neosol, Organosol and Fluvic Neossol have better quality compared to those grown in Oxisol and Litolic Neosol.