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This article in SSSAJ

  1. Vol. 59 No. 2, p. 357-364
    Received: Oct 19, 1993

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Aluminum Transformations and Solution Equilibria Induced by Banded Phosphorus Fertilizer in Acid Soil

  1. J. J. Sloan,
  2. N. T. Basta  and
  3. R. L. Westerman
  1. Department of Agronomy, Oklahoma State Univ., Stillwater, OK 74078



Banded P fertilizer may alleviate Al toxicity in strongly acid surface soils (pH < 5) and is a useful remediation management practice when liming is not possible. The objective of this study was to determine the effect of banded P fertilizer on Al transformations and soil solution composition in acid soils. Pond Creek silt loam (fine-silty, mixed, thermic Pachic Argiustoll; pH = 4.0) was amended with five P fertilizer rates and incubated at 24°C for 70 d. Dissolved Al, Mn, Ca, Mg, K, PO4, SO4, Cl, and NO3, pH, electrical conductivity, and exchangeable cations were measured after 1, 5, 10, 15, 30, and 70 d of incubation. Soil solution Al, Ca, Mg, and Mn decreased but SO4 increased with P fertilizer rate. The concentration of dissolved metals increased and soil solution pH decreased with time. Soil solution Al3+ decreased and Al-orthophosphate complexes increased with P fertilizer rate. Saturation indices derived using MINTEQA2 suggest possible precipitation of Al as gibbsite at low P rates (<175 mg P kg−1) and incubation times ≤15 d, K-taranakite at high P rates (>262 mg P kg−1) and incubation times ≤30 d, and amorphous variscite analogs at all P rates. Soil solution was undersaturated with respect to Ca and Mg phosphates. Formation of MnPO4·1.5H2O was consistent with the well-aerated conditions of this study. Significant (P < 0.05) reductions in exchangeable Al, Ca, and Mg were correlated with P fertilizer rate. Phosphorus additions did not affect exchangeable Fe or Mn. Banded P fertilizer is a viable alternative method to reduce toxic forms of Al in strongly acidic soils.

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