Abstract
Partially acidulated phosphate rock (PAPR) has been shown to be an effective source of P for plants grown on acid soils. Less information in available, however, regarding the effect of the phosphate rock (PR) source on the solubility and agronomic effectiveness of PAPR.
The effect of Fe2O3 + Al2O3 content in PR on the quality of PAPR produced was investigated in this study. Nine sources of PR from Africa, Latin America, and the United States, representing a range of Fe2O3 + Al2O3 from 0.7% to 12.4%, were used. In a single-step process, the finely ground PRs were partially acidulated with H2SO4 at the 30% or 50% acidulation level and granulated (−3.35 + 1.18 mm or −6 + 14 mesh). It was found that the water-soluble P content in PAPR decreased with increasing Fe2O3 + Al2O content in the PR used. Apparently, the presence of Fe2O3 + Al2O3 resulted in a reversion of some of the water-soluble P to citrate-soluble P and sometimes even to citrate-insoluble P.
A short-term (6 weeks) greenhouse study was conducted to evaluate crop response to PAPRs and single superphosphate (SSP); maize, the test crop, was grown on an acid soil (pH 4.5)—Hartsells silt loam (Typic Hapludults). The agronomic effectiveness of PAPRs with respect to SSP (in terms of dry-matter yield of maize) decreased with increasing Fe2O3 + Al2O3 content in PRs. Phosphorus uptake by maize from PAPRs was found to correlate well with water solubility but not with citrate solubility. The results obtained in this study show that the detrimental effect of Fe2O3 + Al2O3 content on the solubility and P availability of PAPR should be considered when selecting a PR for PAPR production.
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Hammond, L.L., Chien, S.H., Roy, A.H. et al. Solubility and agronomic effectiveness of partially acidulated phosphate rocks as influenced by their iron and aluminium oxide content. Fertilizer Research 19, 93–98 (1989). https://doi.org/10.1007/BF01054680
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DOI: https://doi.org/10.1007/BF01054680