Permeabilidade de solos irrigados com águas salinas em função do teor e tipo de argila

Abstract

Soils are natural bodies with individual behaviors, which respond differently to external stimuli imposed by nature and man. The quality of the water affects the soil, which can lead to degradation by the accumulation of salts. In order to evaluate changes in soil permeability with the application of water with increasing levels of electrical conductivity (EC) and sodium adsorption ratio (SAR), vertical column and constant load permeameters were assembled. Horizons of nine soils from Pernambuco State were selected, and chemically, physically and mineralogically characterized. The soils were accommodated in PVC columns and the Ca: Na ratio was adjusted. Then, waters with increasing levels of salts were applied to determine the saturated hydraulic conductivity (Ksat), with water with five EC values (128, 718, 1709, 2865 and 4671 μS cm-1) and five SAR values [0, 5, 12, 20 and 30 (mmolc L-1)1/2]. The data obtained were adjusted to multiple regression equations for Ksat as a function of EC and SAR of the waters. This study also determined the critical SAR value at each EC level, where Ksat was minimal; and the threshold electrolyte concentration (CTH), with 20% reduction of maximum Ksat. The Ksat of the Ferralsol, Nitosol and Lixisol was not altered with the different treatments. In Regosol, Vertisol, Planosol, Luvisol, Cambisol and Fluvisol, Ksat increased with the eraise in EC and decreased with the increment of SAR. CTH was easily reached in soils with higher content of high activity clay. In sandy soils, CTH was only reached with higher values of SAR, indicating greater resistance of these soils to salinization and sodification. The soils of Agreste and Sertão were the most affected by the treatments, indicating serious risks of physical and chemical degradation. The importance of monitoring the quality of the water to be used for irrigation is demonstrated, especially in less weathered, more clayey soils with high activity clay, so that the accumulation of salts in the soil does not intensify further in the semiarid.