Distribution of Phosphorus forms in the Kelardasht Forest Soils

Phosphorus is an essential element for plant that appears in different chemical and biochemical forms in soil, therefore, it is susceptible to effects by pedogenic processes. In order to investigate effect of pedogenic processes on P forms and their distribution, 8 soil profiles were studied in forest land of Kelardasht. Available P (Pav), total P (TP), organic P (OP), mineral P (MP) and 8 mineral P forms were determined in the genetic horizons and the correlation of these forms with each other and also the physicochemical soil parameters were investigated. The results showed that pedogenic process significantly affected distribution of different P forms. Fe-P and Al-P showed significant positive correlation with Pox, which could indicate simultaneous extraction of poorly crystalline Fe-Al oxide (by dissolution) or adsorbed/absorbed P by Al-Fe oxides (anion and ligand exchange). These poorly crystalline forms, octa-calcium phosphate (Ca8-P) and occluded P (Oc-P) correlate positively and significantly with clay content that enhance possibility of these components linkage with clay particles during different chemical reaction and co-migration of P and clay by lessivage and eluviation-illuviation process. Labile mineral P (LPi) and moderately labile mineral P (MLPi) did not show significant correlation with Pav, whereas apatite significantly and positively correlated with Pav. Removal of P from surface horizons can explain this result. Nevertheless, the highest correlation was between Pav, OP, and organic carbon (OC). According to this result, littering and humification may be considered as the most important processes that can influence P availability.