Abstract
The maximum phosphorus adsorption (Smax) and Phosphorous saturation index (Psat) of a soil provide information for the proper management of the P fertilizer of the soil. The objective of this investigation was to determine Smax and develop a Psat for 14 rice soils. Soil samples were analyzed for pH, clay content, dithionite extractable Fe (FeD), Mehlich-3 (M3) extractable P (PM3), and Fe (FeM3). The Smax value and Psat based on M3 extractions were determined. The Smax value ranged from 110 to 625 mg kg-1, and correlated with sand (r =-0.70, P>0.01), silt (r =0.70, P>0.01), clay (r =0.59, P>0.05) and FeD (r =0.71, P>0.01). Soil pHH2O and organic carbon content were not correlated (P>0.05) with Smax, while pHKCl was negatively correlated (r =-0.64, P>0.05) with Smax. Multiple regression found that the combination of pHKCl and FeD were the two most important soil properties related to the Smax of the soils studied. Conventional adsorption equations, such as the Langmuir, Freundlich and Temkin equations, satisfactorily described the P sorption of the soils. The P sorption capacity of the studied soils varied from 80 to 316 mg kg-1. The calculated energy of adsorption of the soils ranged from 0.18 to 1.56 mg L-1, and there was apparently a negative correlation between the energy of adsorption (k) and the observed Smax values. Buffering capacity ranged from 14 to 69. Phosphorus saturation indices (Psat) of the tested soils varied from 1.82 to 28.21%, and were correlated with sand (r =0.56, P>0.05) and silt (r =-0.59, P>0.05), but not with the other soil properties we studied.
