Predicting phosphate fertilizer requirement using sorption isotherms in selected calcareous soils of Western Azarbaijan province, Iran
2003
Samadi, A.
Determining phosphorus (P) fertilizer requirement using sorption isotherms is considered more accurate than conventional soil P tests. To evaluate P requirement sorption test, a glasshouse experiment using wheat (Triticum aestivum L., cv. Omid) was conducted on 14 soil samples belonging to 10 soil series taken from agricultural regions in the south of Urmia, Western Azarbijan province, Iran. The experiment was laid out in a completely randomized design with five levels of P replicated three times. Concentrations of P in solution established by adding P in the pots estimated from the sorption curve ranged from 0.2 to 1.2 mg P/L including check treatment (no P). The phosphate sorption was well described by Freundlich (R2 = 0.96) and Langmuir (R2 = 0.88) isotherms. Yield of wheat in all soils approached maximum as adjusted P levels were increased to 0.4 mg P/L. The results showed that some soils studied were adequate in available P by the NaHCO3 test, but required an amount of P fertilizer by the isotherm P requirement test to obtain maximum biomass production. Using stepwise regression analysis, it was found that a useful regression model for the prediction of standard P requirement (P(0.4)) included the combination of Olsen P and clay content: P(0.4) = 78.4 - 3.7 Olsen P + 0.65 Clay (R2 = 0.54, p < 0.001)
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