Adsorption and desorption of phosphorus in subtropical soils as affected by management system and mineralogy

Abstract

Phosphorus added to soil is only partly available to crops because it is sorbed to some extent by various soil components. The aim of this study was to assess the influence of mineralogy and soil management (either conventional tillage, CT, or no-tillage, NT) on the maximum P adsorption capacity (Pmax), remaining P (Prem), and maximum desorbable P (β) in a Rhodic Paleudult, a Rhodic Hapludox and a Humic Hapludox, all from southern Brazil. Pmax was estimated from the Langmuir equation describing the sorption curve for soil samples and β from a first-order kinetic equation describing successive P extraction with an anion-exchange resin following incubation of the soils with an amount of P equivalent to 30% of Pmax (Padded). Pmax and Prem were significantly correlated with the content of iron oxides (mainly in goethite, Gt). Pmax was lower under NT than under CT in the Rhodic Paleudult and Rhodic Hapludox. On the other hand, Prem was lower under CT than under NT, and exhibited significant differences between the 0–5 and 5–10cm layers under NT. Parameter β peaked in the soil with the highest Pmax but the β/Padded ratio was highest in the Rhodic Paleudult, which was the soil with the lowest content in iron oxides. These results suggest that the soil with the highest Pmax and Gt content (viz., the Humic Hapludox) supplies plants with P at a lower rate than the other two despite its high P desorption potential.