Variabilidade espacial de parâmetros físico-hídricos num solo aluvial da microbacia hidrográfica do riacho São Pedro - Paraíba - Brasil.

Abstract

The objectives of present work was to study the spatial variability of physical-hydrological parameters of an alluvial soil of the hydrological microbasin of the 'Riacho Sao Pedro' in "Paus Branco" Rural Community, located in "Regiao Fisiografica Borborema Oriental" of Cariri Paraibano homogeneous microregion, Campina Grande - PB and try to solve problems on irrigation water management. The alluvial class embraces soils characterized by depositional process and sedimentation of fluvial materials; they consist of alternate layers of stratified sediments without any sequence and pedogenetic evolution. Consequently, they usually form superposed layers of different texture, in agreement with the deposition cycle. Aiming the study of the spatial variability of some physical-hydrological parameters, in a first stage, samples were obtained in "transeto", spaced 50 meters, in equidistant points totalizing 63 samples along a line of 3.15 km. In a second stage, samples were obtained on two 40 x 40 meters grids, spaced 10 meters, in the widest direction of the land. The data was interpreted by the classical statistics and geoestatistics, for general and spatial analysis, for the sampling system in transeto and sampling system in the grids A and B. The variables sand, silt, clay, real and global density, total porosity, field capacity, permanent wilting point and available water for the plants are of bimodal and/or multimodal form with small asymmetry and kurtoses. The variografic analysis of the variables sand, silte, clay, real density, total porosity, field capacity, wilting point permanent and available water, reveal presence of variografic structure in the study area. The spatial correlation and spacial variance, stands out better in the transeto, due the largest number of samples, and also, due to extension of the area, than in the grids A and B, where the area and the number of samples were limited. The textural properties of the soil (sand, silt and clay) presented space dependence in transeto and in the grids A and B. For casual samplings in the transeto and in the grids A and B, must be considered the distance of space dependence for real density and total porosity. The global density showed pure nugget effect in the transeto and in the grid B. Among the hydrological properties of the soil, the field capacity was the most heterogeneous, with a variation coefficient of the order of 44,8%. The field capacity, the permanent wilting point, and the available water for the plants showed a range of space dependence, in the transeto and in the meshes A and B. Considering the limits established by Warrick & Nielsen (1980) and Gomes (1984), the variability of the global density, real density and total porosity were very small in the transeto, as well as in the grids A and B. An small variability was observed for the real and global density and for the total porosity in the transeto and in the grids A and B. The range or areas of influences obtained through the semivariogramas can be used in future samplings with the objective of elaboration of irrigation projects. The ranges obtained for the field capacity, permanent wilting point and available water, are important to decide which irrigation method should be implanted.