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

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 (P-max). remaining P (P-rem), and maximum desorbable P (beta) in a Rhodic Paleudult, a Rhodic Hapludox and a Humic Hapludox, all from southern Brazil. P-max was estimated from the Langmuir equation describing the sorption curve for soil samples and beta 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 P-max (P-added). P-max and P-rem were significantly correlated with the content of iron oxides (mainly in goethite, Gt). P-max was lower under NT than under CT in the Rhodic Paleudult and Rhodic Hapludox. On the other hand, P-rem was lower under CT than under NT, and exhibited significant differences between the 0-5 and 5-10 cm layers under NT. Parameter beta peaked in the soil with the highest P-max but the beta/P-added 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 P-max 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. (C) 2015 Elsevier B.V. All rights reserved.