The objective of this study was to assess the relative efficiency of single superphosphate (SS), partially acidulated rock phosphate (PARP) and fused magnesium thermal phosphate (MTP) as sources of P and other nutrients for eucalypt plantations in two soils of the cerrado region: an alic quartz-sand (50 g kg-1 of clay) and an alic dark-red latosol (230 g kg-1 of clay). Experiments were carried out under greenhouse conditions at the University of São Paulo, Piracicaba, State of São Paulo, Brazil, in 1993. Sub-samples of quartz-sand received 0, 75, 150 and 300 mg kg-1 of P in the soil, and dark-red latosol, 0, 125, 250 and 500 mg kg-1 of P in the soil. The P doses were estimated on the basis of the solubility of the fertilizers SS and PARP in ammonium citrate, and MTP in 20 g L-1 citric acid. Eucalyptus grandis seedlings were grown, individually, in pots containing 5 kg of soil, for 90 days after emergence. Parallel to the greenhouse experiment, soil sub-samples of each treatment, 2 kg weight, were incubated in plastic bags for periods of 0, 10, 20, 40, 60 and 80 days. At the end of each incubation period, they were sampled and analysed. The relative efficiency indexes between the fertilizers indicated that MTP was superior 64% to SS and 57% to PARP, in the quartz-sand. In the dark-red latosol, SS was superior 55% to MTP and 34% to PARP. The MTP was the P source that induced the higher increase in the soil fertility level, with a significant pH increase, reduction of Al concentration and increase in Ca and Mg concentration. The increasing yield of the eucalypt seedlings was highly correlated to P, K, Ca, Mg and Zn uptake. MTP provided the highest uptake of these nutrients in quartz-sand and the lowest uptake of P, Ca and Zn in dark-red latosol. The distinct growing responses to the fertilizers, particularly to MTP and to SS, in both soils, were largely due to secondary effects of the P sources on the soil fertility.
eucalypt; relative efficiency of P fertilizers; single superphophate (SS); partially acidulate rock phosphate (PARP); magnesium thermal phosphate (MTP); cerrados