Phosphorus Fractions of Selected Calcareous Soils of Eastern Azerbaijan Province and Their Relationships with Some Soil Characteristics

Document Type : Research Paper


1 Former Graduated Student, Faculty of Agriculture, University of Tabriz

2 Assistant Professor, Faculty of Agriculture, University of Tabriz

3 Associated Professors, Faculty of Agriculture, University of Tabriz


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.


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