High-purity, 12- to 14-mesh calcitic limestone was mixed into acid soils containing relatively large amounts of either P, Al, or Mn. These mixtures were equilibrated for 12 months, undergoing wetting and partial drying cycles. Samples of each mixture were withdrawn periodically and the limestone particles were recovered, examined, and their rates of solution determined. The surface of the particles equilibrated in the high-P soil developed a porous, white granular coating that was associated with a 31% reduction in the dissolution rate.
Limestone and calcite crystals were treated in the laboratory with solutions containing Fe, Al, and P. Particles treated with phosphate solutions developed visible coatings, and their average dissolution rates were reduced by 27%.
It was concluded that limestone particles react with phosphates in the soil solution, resulting in the formation of a coating on the surface of the particle. This coating reduces the efficiency of the limestone by reducing the rate of dissolution of the particles.