Journal of Crop Production and Processing

  Phosphorus (P) after nitrogen limits agricultural production in most region of the world. Information about P release rate is limited in Hamadan soils. The objective of this research was to study P release in 10 soils from Hamadan province by successive extraction with 0.5 M NaHCO over a period of 1752 h and the correlation of P release characteristics with soil properties and corn plant (Zea mays) indices. The results showed that soil P release began with a fast initial reaction, followed by a slow secondary reaction until 1752 h. The amounts of soil P released after 1752 h ranged from 309 to 586 mg kg^-1. The cumulative P release was evaluated by six kinetics equations. Statistical analysis showed that phosphorus release kinetics were described by parabolic diffusion law, first order and power function equations. The correlation study indicated that soil P release coefficients such as rate constant of first order, parabolic diffusion law, power function equations, P released after 168 and 1752 h were significantly correlated with some soil properties such as Olsen-P, calcium carbonate equivalent, sand and silt. The correlation studies between plant indices and constants of kinetics equation showed that rate constant of first order equation was not significantly correlated with plant indices. Equation constants of parabolic diffusion law, power function and P release after 1752 h were significantly correlated with plant indices. The results of this research indicated that release rate of P is different in soils and is an important factor in supplying available P to plants.