phosphorus fractions of selected calcareous soils of eastern azerbaijan province and their relationships with some soil characteristics

information about forms of phosphorus (p) is important for the evaluation of p status in soil and also understanding of the soil fertility and plant nutrition. to obtain such information and to determine the relationship between the p forms from soil characteristics, amount of different organic and inorganic p forms of 20 soil composite samples of eastern azerbaijan province, iran were determined by sequential fractionation method. according to the results, the amount of total p in soils ranged from 534 to 1061 mg kg-1 with an average of 771.3 mg kg-1. inorganic p concentrations was as follows: apatite (ca10-p) > octacalcium phosphate (ca8-p) > aluminum phosphate (al-p) > iron phosphate (fe-p) > dicalcium phosphate (ca2-p). organic phosphorus concentrations was as follows: moderately labile organic p (mlop) > labile organic p (lop) > non labile organic p (nlop). results showed that calcium carbonate equivalent (cce) with octacalcium phosphate and iron phosphate, ph with octacalcium p, iron phosphate, available phosphorus and organic carbon with moderately labile and non- labile organic p had significant correlations. total calcium and total organic p had significant relationships with organic carbon. total calcium phosphate and total inorganic p also showed significant correlations with the calcium carbonate equivalent. ca2-p, ca8-p, fe-p, al-p, lop and mlop had positive and significant relationship with the available-p, and between different forms of phosphorus ca2-p had highly significant correlation with available phosphorus. also, significant correlations were obtained between various types of phosphorus, which is presumably a reflection dynamic relationship between them in the soil. regression analysis showed that calcium carbonate equivalent presumably is an important effective soil characteristic on distribution of p forms in studied soils.