Abstract
Soil phosphorus availability is the limiting factor for crop production in Pakistan. The objective of the study was to
investigate the phosphorus adsorption as described by Freundlich adsorption isotherm under rainfed conditions.
Ten soil series of Pothwar Plateau were taken for study. These soils are treated with three different P fertilizers i.e
DAP, SSP and NP at equilibrium solution concentration of 10, 20, 40, 60, and 80 µ g ml-1. A decrease in Padsorption with successive increase in equilibrium phosphorus solution concentration was recorded in all the soils
under study. Maximum Freundlich adsorption parameters i.e maximum adsorption (µg g-1) and buffer capacity (ml
g-1) were observed in Chakwal soil followed by Balkassar soil. The minimum values of these two Freundlich
parameters were observed in Kahuta soil. Maximum value of KOC was observed in Chakwal soil with DAP, SSP
and NP while minimum value of KOC was observed in Bather soil with all fertilizers under investigation. The
minimum ∆G -20.19 KJ mol-1, -20.55 KJ mol-1 and -20.28 KJ mol-1 with DAP. SSP and NP, respectively was
observed in Chakwal soil, while maximum values of ∆G was observed in Bather soil. The SSP showed maximum
adsorption on the whole and DAP resulted in minimum adsorption of P fertilizer calculated by Freundlich
adsorption isotherm. Buffer capacity was highest with SSP treatment and minimum with DAP fertilizer treatment in
all ten soils under study. Further studies on P release pattern are suggested under rainfed conditions of Pakistan
which would be important for plant nutrition.
