Abstract
A greenhouse experiment was undertaken to assess the agronomic efficiency of rock phosphates in five savannah soils. Standard response curves (0 kg ha-1, 100 kg ha-1, 200 kg ha-1, 400 kg ha-1, and 800 kg ha-1 of P2O5) with triple superphosphate (TSP) were used, including two rates (200 kg ha-1 and 800 kg ha-1 of P2O5) of alternative phosphate sources (Arad phosphorite - Israel, phosphoric bauxite - Senegal, and Araxa apatite - Brazil). Millet (Pennisetum thyphoides) was used as test crop. Data show the following ranking for agronomic efficiency: phosphorite > bauxitic phosphate > apatitic phosphate. Mehlich-1 extractant solubilizes apatitic phosphates, over-estimating the available phosphorus (P) in soils. Critical levels for Mehlich-1 and resin extractants, to which data of available phosphorus from natural phosphate treatments have been added, differed among each other, but were higher than those obtained with triple superphosphate alone. The extractants behaved in a similar way as related to the extraction of soil available P. KEY-WORDS: Rock phosphates; performance; savannah; millet.
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