Effect of Soil and Foliar Silicon Application on the Reduction of Zinc Toxicity in Wheat

The aim of the study was to compare soil and foliar application of Si to relieve stress in wheat caused by excess Zn in the soil. Two pot experiments were carried out in which the soil was contaminated with zinc sulphate at the dose of 600 mg kg(-1) Zn before sowing. Si was applied in the soil in the following doses 200 mg kg(-1) and 400 mg kg(-1) Si and as foliar spraying in concentrations 2 mM L-1 and 6 mM L-1 Si in the form of sodium silicate. The applied dose of Zn was toxic to wheat and caused a significant decrease in the biomass of shoots and roots. Soil application of Si reduced the negative effect of Zn on plants and significantly increased the biomass of the tested organs. The foliar application of Si did not reduce the decrease of plant biomass. Soil contamination with Zn caused a drastic increase in Zn concentration in shoots and roots, while Si applied in the soil significantly decreased this concentration. The increase in soil pH, which was caused by sodium silicate, also affected the decrease in Zn concentration in plants. The plants absorbed Si applied to the soil, which is indicated by an increase in the Si content in shoots compared to the control. In the case of foliar spraying, only a higher dose of Si increased its concentration in the plants. The application of Si in the soil, in contrast to foliar application, reduced the transfer of Zn from roots to shoots. The higher effectiveness of soil application of Si than foliar application in alleviating the toxicity of Zn was associated with both an increase in pH and a higher uptake of Si by plants.