Phosphorus release kinetics and availability in calcareous soils of selected arid and semiarid toposequences

Abstract

Rate of phosphorus (P) release from solid to solution phase may control the lability of P in soil environments. Kinetics of P release from Iranian calcareous soils at upper-, mid-, and lower-slope positions of two arid and two semiarid landscapes were determined and relations between the P release rate parameters and P uptake by wheat were investigated. The kinetic data was best described by simple Elovich equation as evidenced by the relatively higher values of determination coefficient ( r 2) and the relatively lower values of the standard error of estimate. Power function, parabolic diffusion and first order equations also well fitted the time-dependent P release data. The initial and final P release rates (i.e., DR in and DR f) that were estimated at reaction times of 0.25 and 72 h and the P release rate parameters derived from the Elovich (1 / β), power function ( ab) and parabolic diffusion ( R) equations were well-correlated with the wheat shoot dry matter yield production and the amount and/or the concentration of P in wheat tops both at an early (4 weeks) and a later (10 weeks) stages of growth confirming the importance of P release rate in plant P nutrition in the soils. The rate parameters showed positive significant relationships with clay, active calcium carbonate and citrate–bicarbonate–dithionate (CBD)-extractable Al contents of the soils. The soil properties promoting the P release rate and the P release kinetic parameters increased from the upper-slope to the lower-slope positions of the arid toposequences.