Breakthrough of inorganic ions present in cattle slurry: Soil column trials

Column trials were used to characterize the downward movement of sodium, potassium, ammonium, orthophosphate and chloride (all typically present in cattle slurry) through the soil profile. The soil used was a pasture soil developed over amphibolite; trials were carried out with the < 2 mm fraction, each column being packed with soil from a single horizon. A feed solution containing known concentrations of the above ions was applied to the top of each column, and ion concentrations were determined in outflow samples. Chloride passed through the soil more rapidly than water. Sodium passed through at about the same rate as water (i.e. a retardation factor of about 1). Potassium and ammonium both showed a clear lag (retardation factors of about 1.5–2.5). Orthophosphate was almost totally retained. For all columns, sodium outflow exceeded sodium input, possibly as a result of displacement of soil sodium by other cations in the feed solution; in addition, the time-course of sodium outflow suggests a pulsatile pattern of sorption/release. Differences in the cation retention capacities of the three soil horizons studied appear to be largely attributable to differences in clay content. The retention of orthophosphate is probably attributable to reaction with iron and aluminium oxides, which are abundant in the soil studied.