Phosphorus Fractions of Selected Calcareous Soils of Qazvin Province and their Relationships with Soil Characteristics

摘要

Informations of phosphorus fractions are important for evaluation of their status in soil and understanding of soil chemistry that influence soil fertility. To obtain such information, amount and distribution of P in different fractions of 20 soil samples of Qazvin province, Iran were determined by sequential extraction methods and their relationships with each other and with soil characteristics were investigated. Total P of different soils ranged from 700 to 1040 mg kg~(-1). The clay contents of different samples ranged from 18-52%, CEC from 14.5-33.5 cmol.kg~(-1) and the active CaCO_3 from 2.9-19.4%. The amount of different P forms i.e. dicalcium phosphates (Ca_2-P), octacalcium phosphates (Ca_8-P), Al-phosphates (Al-P), Fe-phosphates (Fe-P), occluded-P (O-P) and P as apatite (Ca_(10)-P) were determined and found to be ranged from; 1.6-42.3,72-314,14.5-54.8,8.4-34.8, 5.9-33.4 and 262-697 mg kg~(-1) respectively. Simple correlation coefficients showed that Olsen-P had a significant correlation with soluble-P, Ca_2-P, Fe-P and O-P.A significant correlation was also observed between the P forms themselves, which is presumably a reflection of the existence of a dynamic relation between the chemical forms of an element in soil. Clay with Fe-P and O-P; total P with Cag-P, Al-P and Ca_(10)-P; CEC with Al-P and O-P have positive significant correlation. Electrical conductivity (EC) with Ca_8-P and Al-P; organic carbon (OC) with Ca_(10)-P and active CaCO_3 with Ca_(10)-P have negative significant correlation.