Evaluation of Si availability in slag fertilizers by an extraction method using a cation exchange resin

A new extraction method for the evaluation of Si availability in slag fertilizers was developed based on findings on the dissolution process of the slags in paddy fields. In the method, the slags were dissolved in water with the addition of a weakly acidic cation exchange resin (H form). The effects of the slag/water ratio, the amount of resin, and temperature on the Si dissolution from the slags were examined in order to determine adequate extraction conditions. The Si dissolution from the slags was enhanced by the addition of the resin. The pH of the extractant was well controlled between 6 and 7 during the extraction. The percentage of the amount of Si extracted by traditional evaluation methods using 0.5 м HCl or an acetate buffer solution to the total amount of Si in the slags was much higher than the Si recovery rate by rice plant (Oryza sativa L. var. Nihonbare) which was measured in our previous study. Moreover, there was no correlation between these values. On the other hand, the percentage of Si extracted by the new method was in the same range as that of the Si recovery rate and a positive correlation was obtained. As a result, Si availability in the slags could be evaluated more precisely by using the method proposed here than by using the traditional methods.