[Evaluation of methods to extract phosphorus available in soils fertilized with phosphate rock]
1995
Perez, M.J.
The purpose of this research work was to compare four soil tests to estimate available phosphorus: Olsen (NaHCO3 0.5M, pH 8.5), Bray 1 (HCl 0.025N + NH4F 0.03N pH 3.0), Olsen modified by Dabin (NaHCO3 0.5m + NH4F 0.5N, pH 8.5) and Mehlich 1 (H2SO4 0.025N + HCl 0.05N, pH 1.0) in soils treated with rough Monte Fresco (MFPR) and RIECITO (RPR) phosphate rocks, partially acidulated phosphate rocks (PAPR) and combination of rough PR with elemental S and its partial substitution with TSP, using the' TSP as reference of the highly soluble P source, in order to choose the more suitable test to predict available phosphorus in soils fertilized with phosphates rocks and, their products. The results showed that available P extracted, by Mehlich 1 solution is higher in treatments with PR than in the treatments with soluble P sources, which does not correspond to plant response parameters and that is the reason of its lower correlation coefficients. The relationships established between solubility of P sources and available P extracted by the four evaluated methods, ratified the suspicion that Mehlich 1 solution dissolves a considerable amount of PR that would not dissolve under field-growing conditions and so it over estimates the real available P in soils treated with phosphate rocks. The correlation coefficients of Bray 1, Olsen and Olsen-Dabin are high and show not significant differences among them.
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