When it comes to Si, it’s all about plant availability

By Graeme Coomer
Managing Director
Maxi-Yield

People fear what they don’t understand and hate what they can’t conquer. The importance of silicon (Si) as a plant nutrient is still relatively unknown to a lot of crop farmers in South Africa.

In agriculture, Si is a nutrient for which an enormous amount of literature examines the value of silicon fertilisation in improving overall crop productivity and health. The benefits of silicon fertilisation are too significant to be overlooked, and in large parts of the world has become common agricultural practice.

Maxi-Yield, through our distribution partner, Laeveld Agrochem, has recently introduced PlantGuard. This is a unique source of plant-available silicon, unlike other sources of silicon on the market, and is produced through and stability, with maximum plant-available silicon.

All research on silicon has proven that plants and micro-organisms can only absorb silicon in the form of monosilicic acid (H4SiO4), so it makes sense for farmers to use a source of silicon which is high in monosilicic acid content. PlantGuard® is a silicon-rich material composed only of ionised liquid monosilicic acid and its oligomers (which are recognised as extra-active forms of silicon).

Monosillcic acid is a difficult product to produce and to stabilise in order for it to remain in this form without crystallising, which is what makes this patented technology so unique. It the monosilicic acid content is known and in a stable form, unlike other silicon products.

It is important to note that the total Si content of a product does not determine its total monosilicic acid content. The fact that Si is the second-most abundant mineral in the soil after oxygen, but yet we have Si-deficient soils, is proof of this. Take sand (silicon dioxide or SiO2) for example. The major constituent of sand is silica, but still these soils are amongst the poorest, if not the poorest monosilicic acid containing soils, because SiO2 is insoluble and hence why we have beaches and sandy soils. PlantGuard is a product in which the monosilicic acid amount is known and can therefore be displayed on the label. This highly concentrated form of plant-available silicon enhances plant vitality and nutrient uptake, boosting plant resistance to biotic and abiotic stress, which as a result leads to better quality yields.

Why is monosilicic acid important for crop farmers?

The beneficial effects of monosilicic become more evident when plants are in biotic or abiotic stress environments. High plant-stress conditions in South Africa seem to be the new normal, and the reduction of plant stress is now more than ever a priority in order to produce crops of a high quality and quantity.

Interestingly, research has shown that silicon can be absorbed by plants at levels equal to or even greater than nitrogen, phosphorus and potassium, which are considered essential for sustainable crop production (Savant et al., 1999). Typically, soils that have been under long-term crop production and sandy soils have a low monosilicic acid content.

Crop production removes large quantities of monosilicic acid. It is estimated that global agricultural crops remove between 520 and 550 million tons per year. Crops such as maize, wheat and sugarcane can remove as much as 300kg to 500kg of monosilicic acid each year. To put the importance of this element into perspective, sugarcane removes only about 100kg of nitrogen per year.

Silicon fertiliser has the capacity to adhere to phosphates in the soil solution, including those released from the exchange reaction between the silicate and the phosphate ions, resulting in the release of phosphates into the soil solution.

Monosilicic acid adds structural strength to plants

Monosilicic acid is absorbed by plants and translocated to sites of strong evapotranspiration in epidermal regions of stems and leaves.

In these areas, the silica forms solid, hydrated gels between the cuticle and the cell walls. Silicon is also deposited within cell walls, where it improves cell wall strength, plant rigidity, root development, linear growth and water efficiency.

Silicon improves photosynthetic activity

The accumulation of Si in epidermal cells and cell walls of plants produces more erect leaf blades, with improved light interception characteristics and increased photosynthetic activity. The application of silicon as a soil amendment has been reported to result in elevated concentrations of chlorophyll per unit area of leaf tissue, resulting in improved photosynthetic efficiency.

Silicon reduces drought stress and heat stress

Silicon alleviates the effects of water-deficit stress and has been attributed to:

(a) The reduction of transpiration through the outer cells.

(b) Improved stomatal conductance.

(c) The stimulation of antioxidants that

(d) Increased chlorophyll content and improved photosynthesis.

(e) Healthier root systems.

The presented research results confirm the beneficial effect of silicon applied to soil or as a foliar application on the quantity and quality of the yield of many plant species.

The effect of silicon as foliar nutrition, which stimulates plants to grow under stress conditions, is particularly beneficial. Such an application should be introduced into plant production as a standard in the cultivation of crops.

In summary

It is alarming that researchers have estimated that agricultural crops account for a staggering 35% of naturally produced monosilicic acid, due to the large biomass of agricultural plants. Silicon accumulation has tripled in the last 50 years and will increase a further 22% to 35% by 2050, resulting in further human-derived disruptions in the Si cycle in future (Carey & Fulweiler, 2015). Researchers have also highlighted the impact that agriculture is having on the global silicon cycle, which, like the phosphate cycle (soil depletion) and the nitrogen cycle (;loss through leaching), affirms that it cannot be ignored in agriculture.