Various methodologies for soil solution sampling are available, but the proportion between gravitational and capilar water is usually unknown. In this study, a sequential extraction system of soil water for determining its chemical composition as a function of the soil porosity is presented. Soil columns were filled by air-dried clay-loam Ultisol. The columns were saturated with distilled water for 24 h, and then the soil solution was sampled at the base of the column by applying the suction equivalent to 0, 13.3, 26.7, 40.0, 53.3 and 66.6 kPa. Volume, pH, electrical conductivity, Na+, K+ and NO3- were measured in the solution. The high correlation (non linear; r² = 0.998) between applied suction and soil matrix potencial, which was assessed by a tensiometer within the soil column, validated the proposed method for sequential soil solution extraction. Ionic concentrations were highly variable in different soil pore sizes, with low concentrations in the soil macroporosity, except for K+, which demonstrated the necessity of standardizing the sampling methodology to avoid incorrect estimation of concentration of solute in soil.
soil column; soil solution; porosity; sodium; nitrate
