The dissolution and dispersion of dicalcium phosphate dihydrate in soils.

SUMMARY A model of the dissolution of a planar source of dicalcium phosphate dihydrate (DCPD) in soil is developed, with which to predict the calcium, phosphate and pH profiles formed by DCPD dissolving in an acid soil. The model comprises numerical solutions of partial differential equations describing the diffusion and reaction of calcium, phosphate and base in soil. The concentrations of calcium, phosphate and hydrogen ions in the soil solution at the mineral/soil boundary are found from the ion activity product of DCPD and by equating the fluxes of calcium, phosphate and base across the boundary. The derivation of the equations, the other boundary conditions, and the simplifying assumptions necessary for the solution of the equations, are discussed. The sensitivity of the model to its input parameters is assessed. The model provides a basis from which to advance to more complex geometries, and more complex fertilizers.