A greenhouse experiment was conducted with rice aiming to evaluate the agronomic efficiency of phosphates soluble in citric acid 2% or ammonium citrate, as compared to the water soluble phosphates and to compare the efficiency between the extractors of resin and Mehlich with the available soil phosphorus. The sources tested were Simple superphosphate (SSP), Magnesium multiphosphate (MP), Magnesium thermophosphate (TP), Araxá rock phosphate (AP) and Gafsa rock phosphate (GP), at the rates of 0, 50 and 150 mg P/dm3. The agronomic efficiency indices (AEI) for the 50 mg rate were 106%, 98%, 95% and 16% respectively for MP, TP, GP when compared to a standard AEI of 100% for SSP. At the higher rate, AEI were, of the same order, 86%, 82%, 84% and 22%, the first three being statistically equivalent to SSP, showing similar efficiencies when compared to water-soluble phosphates. Furthemore, in comparing ion-exchange resin and Mehlich as soil phosphate extractors, the resin was observed to have a much better correlation between soil phosphorus and a) dry matter yield (r = 0,82 resin and r = 0,08 Mehlich) b) phosphorus uptake by rice plants (r = 0,89 resin and r = 0,15 Mehlich).
rice; phosphorus; sources; efficiency; extrator; Oryza sativa
