Soil Phosphorus Availability and Eucalypt Phosphorus Uptake from Soluble and Insoluble Sources of Phosphorus

Abstract

P recovery efficiency from natural rock phosphates and a concentrated phosphate by Eucalyptus grandis plantation in relation to triple superphosphate was evaluated in field trials conducted in the cerrado area of Brazil. Two experiments were carried out in two sites of the Savanna area of Minas Gerais State, Brazil. The rates of the natural phosphates (RP)  Araxa and Patos de Minas(P₂O₅ 24% and Ca 25%),  were 500, 1000, 2000, and 4000 kg/ha and Arafertil (33% -P₂O₅ and 33% Ca)concentrated rock was tested using 1000kg/ha rate only. The triple superphosphate (TP = 45% -P₂O₅ and 13% Ca) was applied at 250, 500, 1000, and 2000 kg/ha. Mehlich -1 and Bray -1 extractants were used to extract P from the soil. The concentration of P extracted varied with the reagent used.  Mehlich-1 extracted about 38.8% more P over the Bray -1 extractant at both sites, although, in one of the sites the extraction was 18% higher than the other. On both experimental sites, application of phosphate from both natural and concentrated forms increased tree height, stem volume and above ground dry matter production, but there was no difference between them at the rate of 1000 kg/ha. P-fixing capacity by trees increased with increasing soil P utilization efficiency. P recovery by the trees varied from 3 to 11% depending on rates and source. But P fixing capacity was higher for TP than for RP.

Keywords: Araxa rock, concentrated arafertil; recovery efficiency, P-fixing capacity and eucalypt.