Communications in Soil Science and Plant Analysis · 2006 · 61 citations · 18 references
AgricultureEarth SciencesSoil SciencesSoil ChemistrySoil FertilitySoil ScienceNutrient AvailabilityPhosphorus CycleSoil Chemical PropertiesSoil CompositionSoil Nutrient AvailabilitySoil Phosphorus ChemistryCalcium Carbonate EquivalenceFractionationPhysicochemical PropertiesSequential ExtractionSoil Phosphorus AvailabilitySoil Phosphorus FractionationSoil Phosphorus SpeciationSoil Solution Phosphorus
Abstract Highly calcareous soils are abundant in Iran. The calcium carbonate equivalent (CCE) of these soils reach up to 650 g kg−1. Although phosphorus (P) fertilizer is being widely used in these soils, little information, if any, is available about P status in such soils. The objectives of this study were to 1) determine inorganic P forms in 18 surface soils of southern Iran, 2) study P readsorption during different stages of fractionation schemes, 3) assess the ability of NaOH to extract aluminum (Al)‐P, and 4) evaluate the relationships between P availability indices and inorganic P forms. Eighteen soil samples with a wide range of physicochemical properties were selected for this study. Inorganic P forms was determined by sequential extraction with NaHCO3, NH4OAc, NH4F, NaOH, citrate dithionite (CD), and H2SO4, which are referred to as Ca2‐P, Ca8‐P, Al‐P, Fe‐P, occluded P (O‐P), and Ca10‐P. Phosphorus readsorption in different stages was determined by 1 M MgCl2. Furthermore, a fractionation scheme without an NH4F step was used to evaluate the ability of NaOH to extract Al‐P. NaHCO3 (Olsen‐P) and MgCl2‐extractable P (Exch‐P) were regarded as P-availability indices. The abundance of different P forms was in the order Ca2‐P<Fe‐P<Al‐P<O‐P<Ca8‐P<Ca10‐P. Ca2‐P was highly correlated with Olsen‐P and Exch‐P. Ca2‐P, Olsen‐P, and Exch‐P showed a relationship with CCE, citrate–bicarbonate–dithionite extractable Fe (Fed), and Al (Ald). Phosphorus readsorption appeared to be important only in the Ca8‐P step, and the content of readsorbed P was related to Ca8‐P, CCE, and clay content of the soils. In the present study, Al‐P and Fe‐P accounted for 10 and 5% of the sum of the inorganic P fractions, respectively, and Fe‐P showed a strong relationship with Feo, whereas Al‐P showed a significant relationship with oxalate‐extractable Al (Alo) and Ald. It was found that one extraction with NaOH is not a good indicator for Fe‐ and Al‐P, and the ability of NaOH to extract Al‐P was reduced with increase in Al‐P content.
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