Abstract
Phosphate fertilizers should match soil attributes to enhance agronomic effectiveness and recovery by plants. The purpose of this study was to test the agronomic effectiveness of P sources varying in water solubility on two soils differing widely in P adsorption capacity (PAC). Soils selected for the study were Oxisols with very low available P and presenting low and high PAC (Ox-LPAC and Ox-HPAC, respectively). Both were limed to pH 5.4 in a greenhouse study conducted utilizing corn as the test crop. Treatments consisted of the two soils interacting with five P sources (monocalcium phosphate - MCP, low-grade single superphosphate - LG-SSP, multimagnesium phosphate - MMP, Arad phosphate rock - PR and a P impurity in triple superphosphate - H14), and four rates of P (12.5, 25.0, 50.0 and 100.0 mg kg-1). A control with no P was added for each soil. The treatments were arranged as blocks with three replicates. Plants were harvested 45 d after germination. Dry-matter yield and P uptake were measured and the relative agronomic effectiveness (RAE) compared with MCP as the standard. When applied in low rates of P (12.5 and 25.0 mg kg-1) the RAE of the alternative sources was higher in the soil with high PAC (45, 66, 39 and 65% in the Ox-HPAC for the LG-SSP, MMP, PR and H14, respectively, as opposed to 24, 40, 14 and 47% in the Ox-LPAC). Results suggest that sources of P with low water solubility can be agronomically more effective in soils with high PAC.
Highlights
Phosphorus (P) is the most used element through the application of fertilizers in tropical soils for plant nutrition (Raij, 1991)
A preliminary study based on soil chemical analysis and P adsorption capacity (PAC) was conducted with the objective of selecting two soils differing in PAC but responding to P addition
Significant effects (P < 0.01) were obtained for all causes of variation (P sources, P rates and soil) and for double and triple interaction, but discussion is based mainly on triple interactions foreseeing the purpose of this study
Summary
Phosphorus (P) is the most used element through the application of fertilizers in tropical soils for plant nutrition (Raij, 1991). This is mainly due to the high P adsorption capacity (PAC) of tropical soils, mostly Oxisols and Ultisols (Sanches & Logan, 1992). The TA fertilizers are high in water soluble P and the most used worldwide (Yamada & Abdalla, 2004). The RP and TP are generally lower in cost per unit of P, less water-soluble and effective under specific conditions of soil management, such as on acid soils high in organic matter, clay content and PAC (Chien & Menon, 1995)
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