Variabilidade espacial da salinidade de um solo aluvial no semiárido paraibano.

Abstract

The problem of salinity in the semi-arid area of the Brazilian northeast requires the accomplishment of studies with relationship to its space characterization, seeking to propose reclamation alternatives and management forms of the affected areas. Therefore, a critical analysis of the data referring to the variables that characterize the salinity constitutes an aspect of fundamental importance. In this context, this work was conducted with the objective to study the variability of the pH of the saturation paste, electrical conductivity of saturation extract (ECe) and exchangeable sodium percentage (ESP), in an alluvial salt affected soil, seeking to get map and to define management strategies for the studied area. The study was conducted in an area of 14.700 m2 of Irrigation Project Capoeira, located in the São José do Bonfim - PB. Soil samples were collected at depths of 0-20; 20-40 and 40-60 cm, following a systematic outline of sampling in 10 x 15 m mesh, obtaining 120 points of observation. The chemical analyses were made according to recommendations of EMBRAPA. The behavior of the data was evaluated by measures of the descriptive statistics and of geostatistical analysis through the semivariograms making and of isolines maps obtained by interpolação methods. Low variability was observed for the pH (CV <12%) and elevated for ECe and ESP (CV>60%), what is usually found for chemical variables of the soil. The spatial descriptive analysis provided the sub-division of the area in two subareas: one normal and other affected. Spherical and gaussian models were adjusted to the experimental semivariograms that presented structure of spatial dependence in the sub-areas and studied depths, and the study of the semivariograms revealed of weak the moderate structure of spatial dependence of the analyzed data, with reaches varying of 20 to 40 m. The maps of isolines of the studied variables, obtained through by kriging and inverse of the square of the distance, allowed to visualize the variability of the properties studied, constituting an important tool for the definition of management strategies, rationalizing costs and facilitating better interpretation of experimental data. On the basis of isolines map of the combination of the variables ECe and ESP, an increase of the salinity levels and sodicity was found with the depth.