Fertilization of plants with silicon is particularly justified in soilless culture in which the roots of plants cannot use silicon resources in the soil. Silicon is the only element that does not harm plants when taken up in excessive amounts and its use in plant fertilization improves the yielding ability of plants and their resistance to various stress factors. The effectiveness of silicon application in growing plants is strictly dependent on both the source of this element, plant species and cultivars. The aim of this study was to determine the effect of root application of colloidal silicon as well as of three types of growing media of different silica content and varying ability to release orthosilicate monomers (rockwool, sand, straw) on yield and chemical composition of greenhouse tomato. The research was conducted in greenhouse in the period 2008–2009. Tomato was grown in an extended growth cycle (22 clusters) using a drip irrigation and fertilization system with closed nutrient solution circulation. Tomato plants fertigated with the nutrient solution enriched with silicon showed significantly higher total fruit yield (15.98 kg·plant^-1) compare to plant grown in control treatments. In the studies not found significant differences in total and marketable yield as well as in mean fruit weight between plants grown in rockwool and straw mediums. The total fruit yield of tomato plants grown in sand was lower compared to rockwool-grown plants. The fruit of tomato grown in sand was shown to have more dry matter (5.52%), total sugars (2.58% FR.W.) and potassium (4.19% DW) compared to rockwool culture as well as significantly the highest amount of silicon. The leaves of tomato fertilized with the silicon-enriched nutrient solution contained more silicon as well as less manganese and zinc compared to control plants.

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