By Karla Garcia
Silicon (also known as silica, Si) is found in high quantities in open field production but is absent in hydroponic nutritional recipes. The lack of knowledge about the role of silicon (Si) in horticultural crops became apparent when using soilless / hydroponic systems.
Research has demonstrated that silicon is one of the most beneficial micro-elements for several plants. However, its role has not been considered as essential in plant nutrition. For this reason Si is not used as a common ingredient in hydroponic recipes. It is the aim of the present article to share the knowledge generated around the role of Si in plant nutrition in order to discuss its possible important function in nutrient recipes.
Despite not being a common ingredient in hydroponic recipes, several beneficial effects of silica have been demonstrated in hydroponic systems (Guntzer et al. 2012; Miyake and Takahashi 1983; Voogt and Sonneveld 2001). The use of Si as a nutrient in plants has shown a positive effect in mitigating environmental and pathogenic stresses. Some authors mention its function as an alternative way to control diseases. However most of the results support its role as a good complement for disease treatment and prevention. Van Bockhaven et al. 2013, demonstrated the induction of a broad-spectrum plant disease resistance by implementing Si as part of the fertilizer in plants. Other studies also showed (Hammerschmidt, 2005) Si as an ingredient with the potential to reduce rates and number of fungicide applications, specifically in control of powdery mildew. This same result has been supported by other studies done by Miyake and Takahashi, 1983 and Vercelli et al., 2017.
Silicon is deposited in plant cells walls helping to avoid pest incidence and damage by fungi. Also, the presence of silicon in cell walls can help to improve resistance to heat and drought contributing in the development of strong and healthy plants. This being the reason why many authors present data supporting its role as a nutrient with the potential to increase yields.
One particular issue in the use of Si in hydroponic recipes is pH. Si has a high pH that can affect some nutrient recipes. Also is difficult to maintain soluble in concentrated nutrient solutions. However, as we know, pH can be controlled. Si can be added as a separate ingredient in a different tank and recommendations indicate to reduce pH in the tank containing Si and water directly.
How much silicon should I use?
Now that we know the positive effects of Si in plants. How can we know which form or quantity of Si can be used in hydroponic systems? The requirements of Si by plants in order to get the beneficial effect of this nutrient can be crop specific. Si can be added in nutrient recipes as silicon dioxide and common ranges used are from 50 to 150 ppm. Being 100 ppm is the most common level. It is important to always start with recommended low levels of Si because too much of this nutrient can affect the uptake of other elements.
It is important to mention that the use of Si complies with current sustainable agriculture EU regulations and is not toxic for humans. Plants can live without silicon, therefore it is not an essential nutrient. However, the more this nutrient is studied the more we know about its role improving plant health and growth.