Soil Phosphate Sorption Characteristics of Selected Calcareous Soil Series of Southern Punjab, Pakistan
To estimate the sorption and desorption capacity of some selected calcareous soils Jhatpat, Miani Pacca and Hadhwar from southern Punjab in Pakistan were analyzed. The sorption isotherms of the three soils yielded different curves. The maximum sorption was recorded in the Miani pacca soil series with value of sorption 201. 23 mg kg-1 which was followed by the Hadhwar series with peak sorption value of 190.04 mg kg-1. The lowest value for sorption was determined in the Jhatpat soil series. Comparing the different models (Langmuir, Freundlich and Temkin), Freundlich model showed good fit to the sorption isotherms with regression coefficient (R2) having value of 0.99, 0.99 and 0. 98 for Jhatpat, Miani pacca and Hadhwar soil series respectively, which was higher than the other two models used. The study on the effect of equilibration time (1, 10, 30 and 60 days) of applied inorganic Phosphatic fertilizers i.e. Single super phosphate (SSP) and diammonium phosphate (DAP) @ 60 and 120 kg ha-1 on two soil series with highest P sorption. The P sorption increased with increase in the time of equilibration, with higher value of extractable P was found 22.246 mg P kg-1 after 1 day of incubation, and it gradually decreased with the lowest value of 8.271 mg kg-1 after 60 days of incubation.