Abstract: One of the most serious problems in areas indicated for irrigation projects in the Brazilian Northeast region is the occurrence of sandy soils, known to have low moisture retention, but occurring in strategic locations in terms of water supply and geographical situation, and which can be used for agricultural purposes. The objective of this study was to evaluate the influence of particle size distribution and porosity on the water retention capacity of sandy soils in the semiarid area of the Northeast region. Soil bulk and particle densities, total porosity (macro, meso and microporosity), field capacity, permanent wilting point and soil-water retention curve were determined in samples of surface (A) and subsurface (C or Bw) horizons of ten sandy soil profiles. Particle size was determined subdividing the sand fraction into five classes. Higher amounts of the medium and fine sand fractions of the studied soils oriented their physical and hydric characteristics, being responsible for their great water retention. The arrangement of the fine silt, clay, fine sand and very fine sand particles may have provided a diversity of pore sizes and a good pore distribution, being responsible for the large proportion of micropores in the soils, allowing great water retention capacities.

RESUMO A bacia do rio Natuba é um importante polo de produção de hortaliças para o abastecimento, sobretudo, da zona metropolitana do Recife. O planejamento racional do uso das terras nesta bacia se faz necessário para assegurar a conservação deste recurso. Este trabalho objetivou realizar o zoneamento da aptidão agrícola das terras do médio curso da bacia do rio Natuba - PE, considerando o emprego da média (manejo B) e alta (manejo C) tecnologias. A análise baseou-se nos critérios: deficiência de fertilidade, deficiência de água, excesso de água, suscetibilidade à erosão e impedimentos à mecanização. Os resultados indicaram que as formas de uso conservacionistas, mais recomendados são a pastagem plantada e lavouras, de forma restrita, no manejo B. A possibilidade de utilização do solo no manejo C se restringe à unidade dos Latossolos, posicionada em áreas de topo, e dos Gleissolos no ambiente de várzea. O uso atual praticado na área de estudo, somente, em parte está em conformidade com a aptidão agrícola das terras. Nas encostas íngremes, o uso intensivo com agricultura irrigada, está em desacordo com o potencial de uso agrícola. Técnicas de manejo que visam à utilização do solo de modo conservacionista devem ser implantadas em toda área.

ABSTRACT The basin of the river Natuba is an important vegetable production polo for supplies, especially to the metropolitan area of Recife. Rational planning of the land use in the basin is needed to ensure the conservation of this resource. This study aimed to carry out the zoning of the agricultural potential of the land in the middle course of the river Natuba basin - PE, considering the average (management B) and high (management C) technologies application. The analysis was based on the criteria: fertility deficiency, water deficiency, excessive water, susceptibility to erosion and impediments to mechanization. The results indicated that the most recommended conservationist ways of land use are planted crops and pasture, narrowly, in the management B. The possibility of land use in management C is limited to the unit of Latosols located in top areas, and Gleysols in the environment of floodplain. The current use practiced in the studied area complies only partly with the agricultural potential of the land. On the steep slopes, the intensive irrigated agriculture doesn't combine to the agricultural potential use. Management techniques related to conservationist ways of soil use should be deployed throughout the area.