Long-term dissolution characteristics of various fertilizers made of steelmaking slag in a desalted paddy soil environment (recovery of a paddy field damaged by the tsunami using fertilizer made of steelmaking slag-2)

To evaluate the effect of steelmaking slag as fertilizer in a flooded paddy field, a soil-filled column testing method was developed. The original soil and the soil after desalting with and without fertilizer made of steelmaking slag were used. Three brands of fertilizer with different compositions and phase ratios were evaluated. The results showed a pH increase and Ca supplement after the application of fertilizer made of steelmaking slag, and these changes were independent of the brand. The dissolution of Ca was higher when fertilizer with high CaO concentration was used. The composition of the fertilizer had an effect on cation dissolution behavior not only of Ca, but also of Mn, Si, and Mg. The cation mass balance before and after the experiment was studied. Most of the Na was contained in the water and was washed out during the experiment. The application of fertilizer did not affect the residual Na concentration clearly. The amount of Ca supplied by the fertilizer was almost the same as that contained in the soil, and a signifcant difference in the amount of Ca was observed between the fertilizer brands that used. In addition, it was deduced that free-CaO and the solid solution phase of 2CaO·SiO₂ and 3CaO·P₂O₅ was dissolved and supplied additional Ca during the experiment, but the matrix phase was not dissolved and, thus, remained in the soil.