Chemical Extractants to Evaluate the Silicon Available in Soils Under Steel Slags Application.

Research shows the beneficial effects of silicon application to plants. Although many methods have been used to assess Si availability to plants, the results are controversial, indicating the need to identify more promising extractants with high-potential to determine Si availability in the soil. This study aimed to compare three silicon extractants (CaCl₂, acetic acid 0.5M and resin) to quantify Si content in the soil with steel slag added. The experiment was carried out at the São Paulo State University - UNESP in Botucatu, Brazil. The treatments consisted of two application methods (incorporated and surface) of limestone (L) and four silicates sources: steel slag (SS), ladle furnace slag (LFS), stainless steel slag (SSS), wollastonite (W) and the control without silicate application. The dose applied of each material was calculated to raise the base saturation to 70, the Si contents provided with the limestone and silicates application were 0.15; 1.0; 1.3; 1.6; 1.2; Mg ha^-1 with L; SSS; SS; LFS and W, respectively. The Si content in the soil was analyzed 12 months after application, at  0-20 cm. The extractants showed different Si contents, CaCl₂ showed low Si content in the soil; acetic acid and ion exchange resin was high. The resin application followed the methodology adopted for São Paulo State in Brazil to quantify phosphorus. Further studies should investigate this method to quantify silicon. Regardless of the extractant used, the results were similar.  Slag was similar in providing Si to the soil and LFS was the most efficient. Although the application of different Si sources increased the Si content in the soil, this increase was not observed in the oat plant. Correlations between the extractants and Si uptake in oat plants were low. There was high correlation between the CaCl₂ method and acetic acid method. For the other methods, the correlation was low.