Effect of Aluminum and Iron Oxides on Hydraulic Conductivity of Sandy Loam Soil

Abstract

Iron and Al oxides and hydroxides have been shown to stabilize pure clay systems from the effect of high exchangeable sodium percentage (ESP). This study examined the effect of Fe and Al additions on the stability of a California Alfisol with serious crusting problems. Changes in saturated hydraulic conductivity were used as a measure of treatment effectiveness. Saturated hydraulic conductivity (HC) of a sandy loam equilibrated with sodium adsorption ratio (SAR) 20 CaCl₂-NaCl solution and leached with distilled water was faster for samples treated with 20 and 40 mmol kg⁻¹ of FeCl₃ or AlCl₃ compared with untreated and 10 mmol kg⁻¹ treatments. The FeCl₃ treatments were more effective than AlCl₃ treatments in maintaining HC. Analysis of the column effluent showed that more Al than Fe was removed during leaching. Much of the Fe added to the soils is recovered in oxalate and citrate-bicarbonate-dithionite (CBD) extracts, but little Al is recovered because the added Al is removed with the effluent. The stabilizing effect of hydroxy-Fe polymers against the deleterious effect of exchangeable Na was related to the charge on the polymers and not with the total amount extracted.