Hidropedologia de solos arenosos do agreste de Pernambuco

Abstract

The Neossolos Regolíticos (Regosols) soils are considered very fragile because retain little water, are susceptible to erosion, and are therefore difficult to be managed. In the Northeast of Brazil, these soils are found in highest concentration in the state of Pernambuco. It is important the study of their physical attributes, to indicate the best type of management to be applied. This study aimed to characterize the physical and hydric behavior of four Neossolos Regolíticos located in the Agreste region of Pernambuco, identifying the attributes that can better characterize them. Four profiles were selected in the municipalities of São Caetano (Profile 1), Lagoa do Ouro (Profile 2), Caetés (Profile 3) and São João (Profile 4). In each profile samples were collected at 0-20 cm, 20-40 cm, 40-60 and 100-120 cm, with three replications. Disturbed soil samples were collected and prepared according to EMBRAPA (1997), to perform physical analysis (particle size, bulk density, particle density, aggregate stability). Undisturbed samples were collected to determine soil density and water indicators (water available - WA, saturated hydraulic conductivity – Ksat, Curve Water Retention Feature Ground - CCRAS; pore size distribution, porosity, macroporosity, mesoporosity and microporosity). Also undisturbed samples were collected using the volumetric Kopeck ring, witch 5 cm in diameter and 2.5 cm high, according to EMBRAPA (1997), which were prepared and saturated to perform subsequent analysis. The CCRAS were built linking the data of potential with their volumetric moisture contents obtained. Adjustments were made of CCRAS using procedures according to Van Genuchten (1980), making the use of software "Retention Curve" – RetC (Van Genuchten et al., 1994) to determine the equation parameters. Data were submitted to analysis of variance (ANOVA) and the means were compared by Tukey test at 5% probability using SAS statistical software, version 2.0 student. The soils have in some depths, significant quantities of the finer fractions of sand, silt and clay, enabling the available water remains in the soil for longer. The largest amounts of fractions fine sand, very fine sand and mostly silt and clay of Neossolos Regolíticos studied, guided physical-hydric behavior of these soils, and these fractions account for the largest soil water retention. The moisture retention by profile, due to the deflection between -10 kPa and -33 kPa points, had the following sequence: profile 2 < profile 1 < profile 3 < profile 4.