Mixed-species plantations of <I>Eucalyptus</I> and <I>Acacia mangium</I> increase labile carbon and phosphorus levels in Ferralsol soils in the Cerrado biome, Brazil

Abstract

In order to clarify the effect of mixed planting in the dynamics of phosporus (P), we assessed the fractions of this element in mixed plantings of Eucalyptus urophylla × E. grandis (Urograndis) and Acacia mangium in a tropical soil clay, analysing changes in the fractions of P and examining the correlation of these changes with the fractions of soil organic matter. Pure stands of Urograndis (E) and A. mangium (A) (0A:100E and 100A:0E) and mixed stands of the two species (50A:50E and 37A:66E) were established. The fractionation of P, the granulometric fractionation of organic matter and the labile carbon (POXC) were determined at soil depths of 0–5 and 5–10 cm. Regarding the availability of P, organic parts contributed 34.6% to 38.1% relative to the total P, with the highest percentages being observed for the moderately labile fraction. Highest levels of labile organic P were observed in the mixed plantations. About soil carbon (C), the highest levels of the more labile C fractions were recorded in plantations in which Acacia was present. Mixed plantations were found to show a greater balance between labile P and C fractions. The C fractions warrant particular attention in future studies, notably those related to the emission of greenhouse gases.

Keywords: forest nutrition, fractionation of phosphorus, organic carbon, organic phosphorus