Evaluation of Some Extraction methods for Determination of Corn Available Phosphorus in Some Calcareous Soils of East Azerbaijan Province

In this research, evaluation of Some Extraction methods for determining available phosphorus of the corn plant in 25 calcareous soils was implemented using surface soil (0-30 cm) samples. The experiment was carried out as a factorial in a randomized complete blocks design with cultivation of corn in three replications under greenhouse conditions. Methods of distilled water, calcium chloride, Paauw, Olsen, Colwel, Soltanpour, Morgan, Kelowna-2 and filter paper impregnated with iron oxide were applied, and the available P and the correlations between the resulted values with soil phosphorus fractions were investigated. The maximum and minimum amounts of P were extracted by the methods of Colwel and 0.01 M CaCl₂ respectivly. Among the chemical extraction methods of P, the highest correlation was observed between the Colwel and Kelowna-2 methods. The Soltanpour method had the highest correlation with the paper strips method. Most of the extraction methods showed significant correlations with the labile organic phosphorus (LOP) and moderately labile organic phosphorus (MLOP) fractions, of which the maximum values were related to 0.01 M CaCl₂ and distilled water methods, respectively. Also, all the extraction procedures, were, highly correlated with the dicalcium phosphate (Ca₂-P) fraction among which the lowest belonged to the Paauw method. The amounts of total-P in soils were significantly correlated with  the amounts of extracted P using all the extractants. In this experiment, the methods of Olsen and Colwel had the highest correlations with corn shoot dry weight, but due to the cost increase and longer time of extraction in the Colwel method, the Olsen method was introduced as the preferred one.  The results of this study showed that although the paper strips method could predict corn growth parameters well, but the chemical extraction methods were superior.