Availability and critical levels of phosphorus in maize and soils fertilized with phosphate sources

Abstract

This study had as objective to evaluate the availability and the critical levels of phosphorus in maize plants, by different chemical extractors, in two soils (Ultisol and Oxisol) with different phosphorus (P) adsorption capacity factor and fertilized with Gafsa rock phosphate or triple superphosphate. The results showed that Mehlich-1, Mehlich-3 and Bray-1 were equally efficient in the evaluation of P availability in the treatments with triple superphosphate. For the rock phosphate only the extractors Mehlich-3 and Bray-1 were adequate in this evaluation. The highest values of critical level in the soil, with exception of the Mehlich-1, were observed in soils fertilized with triple superphosphate. The critical level of phosphorus in the shoot dry matter was inversely correlated with the capacity factor of soil and directly correlated with the solubility of the phosphorus source. The necessary dose to reach this critical level was directly correlated with the capacity factor and inversely correlated with the solubility of the source. The triple superphosphate provided higher concentration of P in the shoot dry matter and was more efficient than rock phosphate in the production of dry matter in the Oxisol.