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Abstract:

Water flow in soil is a complex environmental process, which is very important not only for soil formation conditions in the nature, but also for plant development and leaching of nutrients and pollutants toward groundwater. The purpose of this work is to develop a research device intermediary between small-sized soil columns and lysimeters, as well as an adequate research method, to determine soil water permeability and flow conditions in undisturbed soil columns aiming to find out the maximum steady-state water flow values under continuous water supply in order to help investigate the movement of pollutants and fertilizers toward groundwater. The study was carried out in undisturbed soil columns, 0.3 m in diameter and 1 m length, in various environments: loamy Cambic Chernozem (CZca), a loamy-clayey chernic-argic phaeozem (FZce-ar) and a sandy textured eutric psamosol (PSeu). Water was applied according to the soil infiltration rates, and it was found that the steady-state effluent rate (Vef, mm h-1) under continuous water application, as a product of hydraulic conductivity and gradient, and existing in nature after long rainy periods, is generally lower than the saturated hydraulic conductivity (Ks, mm h-1) of all soil horizons, including the most compacted or clayey horizons, due to the different flow type, the unsaturated type for the columns’ Vef and the saturated one for small cylinders’ Ks, respectively. In the case of high clay-content, swell-shrink compacted soils (FZce-ar), there is water infiltration until the soils get wet to values higher than field capacity, then the flow ceases due to clay swelling. The steady-state Vef, achieved after important amounts of continuous water application and practically equal to the steady-state infiltration rate, is the maximum value of soil water flow in the column, because it occurs under submersion conditions at the soil surface, but in unsaturated soil conditions deeply in the column. After cessation of water application, redistribution between the soil horizons occurs for a longer period, and Vef slowly decreases and finally ends after 3-10 days, depending on soil texture and porosity. This flow type is specific for wet and cold seasons when there is a predominantly descendent water movement. Normally, in the other seasons with high evapotranspiration, lower rainfall, and when water infiltration occurs occasionally in the field, Vef would present lower values. The experiments could also involve plants grown under controlled atmospheric conditions. Leaching of soluble nutrients and pollutants depends on the magnitude of Vef, because the movement of these substances cannot exceed the steady-state Vef for all soil columns, and also for subsoil and the underlying geological deposits, simply because the water is their transport agent. Thus, Vef might be an important variable in modeling the leaching of some substances from the soil.