Identification of Optimal Concentration of Silicon Application and Its Roles in Uptake of Essential Nutrients in Soybean (Glycine max L.)

We conducted two experiments to identify the roles of silicon (Si) application in the uptake of essential elements by soybean plants. First, we applied five concentrations (1, 2, 4, 6, and 8 mM) of Si (sodium metasilicate) to hydroponically grown soybean plants. Chlorophyll content and chlorophyll fluorescence showed improvement at 1 mM and 2 mM Si treatments as compared to that of the control. The 2 mM Si application exhibited more highly improved chlorophyll fluorescence values as compared to that of 1 mM Si treatment. We regarded 2 mM Si as the proper concentration for soybean plants. Second, we applied 2 mM of Si to 15 soybean cultivars and measured the concentration of nitrogen (N), phosphorus (P), potassium (K), and Si. Si content increased in the Si treatment; however, two cultivars (‘Dachae’ and ‘Jinpung’) showed reduced Si content despite the Si supplementation. The N and K content in several cultivars decreased after Si application to soybean plants, whereas the P content of most of cultivars was slightly increased after Si treatment. Si did not show any correlation with N, P, and K after Si treatment; however, Si exhibited a significant negative correlation (r = -0.83) with N in the control.