Leaching Characteristics of a Layered Field Soil

Abstract

Two ponded flow experiments were conducted to study the leaching characteristics of a layered field soil, fine sandy loam over coarse sand, with a water table at a depth of 1.8 m.In the first experiment a steel cylinder 1.8 m in diameter was driven into a soil to a depth of 3.6 m. Infiltrations of water and dye provided the means for direct observation of the effect of air entrapment upon the rates of infiltration as well as the primary pattern of water flow through the coarse subsoil. The rate of infiltration was observed to increase by nearly twofold when the entrapped air between the saturated surface layer and the shallow ground‐water table was vented directly to the atmosphere. Removal of the soil layers following infiltration of a dye solution showed that most of the infiltrating water moved through fingers ranging from 5 to 20 cm in diameter.In the second experiment, chloride distributions at six depths were measured following the application of a pulse of 0.3N CaCl₂ solution to the soil surface. Chloride movement for the 20− to 60−cm soil depths averaged about 50% slower than that determined from the average pore‐water velocity at the soil surface. In contrast to this relatively low rate of chloride movement, several salt pulses reached the 120− and 180−cm depths soon after or before reaching the 60−cm depth. This greatly increased flow rate corresponds to the observations in the first experiment where flow became unstable and the solute moved in fingers of flow below the 60−cm depth.