Phosphate sorption by Sri Lankan soils used for rice production: Relation between Tempkin sorption coefficients and soil and plant parameters

The common soil-P tests are unable to distinguish between P-deficient and P -sufficient Sri Lankan soils used for rice cultivation, therefore adsorptio n experiments were performed to determine whether sorption parameters as ob tained from the Tempkin equation are more appropriate. Phosphate sorption i s mainly governed by amorphous Fe- and Al-hydroxides and (or) oxides, clay content and its mineralogy, soil carbon content, and the amount of gibbsite . Removal of Dart of the available P with the Pi-P test prior to the sorpti on experiment, affected the so-called P sorption maximum, a but not the soi l buffering capacity, b. Soil extraction with oxalate reduced both sorption parameters (a and b) significantly. A negative correlation was obtained be tween Tempkin sorption coefficients the per cent shoot P and yield (only fo r buffering capacity). Using the P-sorption data it can be explained why so me fields responded to P and some did not.