The knowledge on different plant abilities to take up soil phosphorus and its use for growth can be important to improve markedly the efficiency of phosphorus fertilization. Having this in mind, an experiment was carried out under greenhouse conditions to test the hypothesis that eucalyptus seedlings are more efficient than rice in absorbing phosphorus from low solubility sources applied to a Quartzamment soil, testing different efficiency concepts. The phosphorus sources Ca(H2(32)PO4).H 2O, CaH32PO4.2H2O and Ca3(32PO4)2 , synthesised in laboratory and identified by X-ray difratometry and thermal differential analyses, were used as radioactive tracers. It was concluded that rice is more efficient in absorbing phosphorus from these low solubility sources, while eucalyptus presents a higher coefficient of biologic P utilisation. The "difference" method (conventional) that in based on P recovery by plants, underestimated the absorption of this nutrient for both species in relation to the isotopic method.
phosphorus absorption; fosfated fertilizers; synthesis of fosfated fertilizers; isotopic labbeling
