Effect of water flow and sampling volume on the functional characterization of pores in an Ultisol

Abstract

The porous system controls the movement of fluids and its description must consider its volume, distribution and functionality. The aim of this work was to evaluate the functional heterogeneity of the pore system of a volcanic ash soil, considering both the sampling volume and the changes in soil structure under conditions of saturated flow. The pore system of an Ultisol (Cudico soil Series) was characterized using non-disturbed samples collected in cylinders of 110 and 250 cm³. The water retention curve, air filled-porosity (ԑa ), air permeability (ka ), saturated hydraulic conductivity (kf), pore continuity and the volume of blocked pores (ԑb ) were determined. Besides, it was evaluated how the amount and functionality of the porous system is affected by a constant flow of water for 24 h. When comparing both sampling volumes, statistical differences were found in the capacity of the soil to retain water and in ԑa at water tension lower than 60 hPa. The saturated flow of water generated a loss in the drainage pores, a decrease of ka and an increase in the number of blocked pores and the continuity index k2 . Therefore, the conditions of saturated water flow alter the soil structure affecting the functionality of the pore system, being this factor more relevant than the volume of the sample when characterizing the pore functionality of the soil.