Kinetics of Phosphate Release from Three Phosphate-Treated Soils
摘要
Phosphate release from three selected soils after treatments of 1.6 and 2.4 mmol L-1 P was investigated using sequential extractions and fitted using six kinetic models, including zero order (Z), first order (F), second order (S),parabolic diffusion (PD), two constant rate (TC), and Elovich type (ET) equations. The results showed that the rate of P release was initially rapid and then gradually declined with time. Also, P release increased with added P. Total P release followed the order: paddy soil with 2.4 mmol L-1 P ＞ red soil with 2.4 mmol L-1 P ＞ paddy soil with 1.6 mmol L-1 P ＞ fluvo-aquic soil with 2.4 mmol L-1 P ＞ fluvo-aquic with 1.6 mmol L-1 P ＞ red soil with 1.6 mmol L-1 P. For the two P treatments P release from the paddy soils in the first extraction was 44.3% and 45.6% of total released P, respectively,which were higher than those from red and fluvo-aquic soils. The ratio of P release at the end of release time was 14.0%and 13.1% in the paddy soil treated with 1.6 and 2.4 mmol L-1 P, respectively, but only 5.1% and 9.2% in the red soil and 7.0% and 5.2% in the fluvo-aquic soil, respectively. Comparison of the coefficients of determination (R2) indicated that ET, TC, and PD equations could describe the P release data better than Z, F, and S equations.