Evaluation of the Status of P Fractions and their Relationships with Selected Soil Properties in Some Calcareous Soils

Effective soil phosphorus (P) management requires the understanding of P forms and its availability. The amount and distribution of P in different fractions of 15 soil samples of Fars province, Iran were determined by sequential extraction methods. The relationships of the P distribution among each other and with soil characteristics were investigated. Total P of different soils ranged from 349 to 994.3 cmol.kg^-1. The clay contents of different samples ranged from 18% to 53%, CEC from 8.5 to 24.9 (cmol(+)kg^-1) and the CCE from 20.6% to 64%. The amount of different P forms Ca2-P (dicalcium phosphates), Ca8-P (octacalcium phosphates), Al-P (Alphosphates), Fe-P (Fe-phosphates) and P as Ca10-P (apatite) were determined. The relative abundance of other inorganic P forms was in the order of Ca10 – P Ca8- P Al –P Fe-P Ca2-P Occl-P. Simple correlation coefficients showed that Olsen-P had a significant correlation with total-P, Ca2-P, Ca8-P and Al-P. A Significant correlation was also observed between the P forms, which is presumably a reflection of the existence of a dynamic relation between the chemical forms of Phosphorus in soil. Clay with total-p and Apatite; total P with Olsen, Al-P and Organic-P; CEC with total-P and Organic-P have positive significant correlation. Sand with Ca10-P and Al-P; organic-p and Al-P with pH have negative significant correlation.