Condutividade hidráulica não saturada de um Argissolo Amarelo Distrocoeso: método do perfil instantâneo

Abstract

Hydraulic conductivity is an important attribute for irrigation, drainage, and soil and water conservation, as it expresses the ease with which a soil conducts water in depth, being strongly influenced by the presence of densified subsurface layers, reducing the water dynamic in the soil profile. The objective of this work was to determine the hydraulic conductivity in a saturated and unsaturated condition of an Argissolo Amarelo Distrocoeso (Densic Acrisol; Ultisol) located in the Coastal Table region in the county of Cruz das Almas, Bahia, Brazil. Was used the instantaneous profile method, in order to identify the soil layers that limit water conduction and to determine the functions K(θ) for each depth. The experiment was conducted at the Federal University of the Recôncavo of Bahia, in an area under pasture. Experimental plot was installed with ten mercury tensiometers installed at 0.1; 0.2; 0.3; 0.4; 0.5; 0.6; 0.7; 0.8; 0.9; and 1.0 m depths for monitoring the soil matric potential and the total potential gradient of water at these same depths. The moisture corresponding to each matric potential was estimated by soil water retention curves adjusted for such depths. Saturated hydraulic conductivity was lower in the 0.30 and 0.80 m depths of the evaluated Argissolo Amarelo Distrocoeso (Densic Acrisol; Ultisol). The presence of thickened layers at the 0.30 and 0.80 m depths, typical of coastal table soils, slowed the conduction and movement of soil water. The determination of unsaturated hydraulic conductivity by the instantaneous profile method allowed to evaluate the differences and possible changes that occur in the soil profile structure. The instantaneous field profile method did not allow to correctly evaluate the K(θ) function for soil moisture close to saturation, since the internal water drainage process occurred quickly. The slope of the ln K versus θ curve was lower at the 0.70 m depth, indicating a smaller K decrease with the θ reduction. In increased scale were located the depths of 0.60, 0.80, 0.50, 0.20, 0.30, 0.90, and 0.40 m, the latter presenting the largest K decrease with the θ reduction.