The second most abundant element on earth silicon is classed as quasi-essential by crop nutritionists. As such it is required by some plants and not apparently by others. In general silicon is needed by most cereals and other monocots but amongst the dicots there are relatively few examples with specific requirements. Crops where silicon deficiency is of economic importance include rice, sugar cane, bamboo, cucumbers, roses and grapes.
In the soil soluble, plant available silicon (orthosilciate) is relatively unaffected by pH but easily leached. In normal soils a balanced equilibrium between soluble silicon and the vast amount of insoluble silica is usually established and deficiency situations are unusual. Uptake by plant roots is both passive and active and translocation is via the apoplastic transpiration stream.
Insufficient levels of silicon are regularly found in soil-less growing systems such as hydroponics and where artificial (eg. peat, coir) growing media is used. Here sensitive crops can be detrimentally affected.
The role of silicon in plants is mainly protective and where levels are adequate then tolerance to fungal diseases such as powdery mildew (“Erysiph” spp) is increased. Very specifically, Roses deficient in silicon are more prone to black spot (Diplocarpon rosae) attack.
Silicon also has various physiological roles increasing the strength of plant tissues, improving colour and appearance and mitigating the effects manganese deficiency. Optimum silicon nutrition increases lodging resistance in cereals and the aesthetic value of ornamentals can be improved.