Inorganic Phosphorus Fractionation of Highly Calcareous Soils of Iran.

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 NaHCO 3 , NH 4 OAc, NH 4 F, NaOH, citrate dithionite (CD), and H 2 SO 4 , which are referred to as Ca 2 ‐P, Ca 8 ‐P, Al‐P, Fe‐P, occluded P (O‐P), and Ca 10 ‐P. Phosphorus readsorption in different stages was determined by 1 M MgCl 2 . Furthermore, a fractionation scheme without an NH 4 F step was used to evaluate the ability of NaOH to extract Al‐P. NaHCO 3 (Olsen‐P) and MgCl 2 ‐extractable P (Exch‐P) were regarded as P-availability indices. The abundance of different P forms was in the order Ca 2 ‐P [ABSTRACT FROM AUTHOR]