Summary
A low-soluble phosphate rock from Patos (Brazil) was compared with monocalcium phosphate, and Gafsa and Morocco phosphate rocks as a source of phosphate for sorghum growing in three acid soils from Southern Bahia (Brazil). Before the test period with sorghum the four phosphates were allowed to react with the soils for 0,90, 180 and 270 days. The effectiveness of each source was assessed as the monocalcium phosphate (MCP) equivalent at zero reaction time.
The MCP equivalent of the low-soluble phosphate rock was poor in all three soils; it increased with reaction time in an ultisol with comparatively high buffer capacities for calcium and phosphate, but did not change with reaction time in the other two soils. With increased reaction time in an oxisol there was a rapid decrease in availability of the monocalcium phosphate, and a less rapid decrease in availability of Gafsa and Morocco phosphate rocks.
The results support the hypothesis that the rate of solubilization of phosphate rock is high in soils of low pH, and with high buffer capacities for calcium and phosphate. Soils with these properties should be selected for field experiments with low grade phosphate rock such as Patos.
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Cabala-Rosand, P., Wild, A. Direct use of low grade phosphate rock from Brazil as fertilizer. Plant Soil 65, 351–362 (1982). https://doi.org/10.1007/BF02375056
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DOI: https://doi.org/10.1007/BF02375056