Silicon is the second most abundant element in soils, the mineral substrate for most of the world's plant life. In spite of silicon as a mineral constituent of plants, it is not counted among the elements defined as "essential," or nutrients, for any terrestrial higher plants except members of the Equisitaceae (*They are commonly known as horsetails, fields growing horse tails could be deficient in silicon).
Going back to the time of Justus von Liebig, who tested both soils and plants for silicon, found it in all cases, was unable to prove it was an essential nutrient by excluding it from plant media, and thereafter dropped it from his tests. However, we are only now beginning to better understand the role of silicon in plant health and disease. Ample evidence is presented that silicon, when readily available to plants, plays a large role in their growth, mineral nutrition, mechanical strength, and resistance to fungal diseases, and adverse chemical conditions of soil.
It is important to note that we need boron to activate silicon. In almost every test I read, boron is deficient. Once we have boron levels adequate we need to look to Silicon. Silicon improves nutrient transport up into the plant. It is found as a component of cell walls.
Plants with supplies of soluble silicon produce stronger, tougher cell walls making them a mechanical barrier to piercing and sucking insects. This significantly enhances plant heat and drought tolerance. Silicon has also shown benefits reducing populations of aphids on field crops.
Tests have also found that silicon can be deposited by the plants at the site of infection by fungus to combat the penetration of the cell walls by the attacking fungus. Improved leaf erectness, stem strength and prevention or depression of iron and manganese toxicity have all been noted as effects from silicon.
Although many soils and especially sandy soils are silicon-rich, soluble silicon content is usually very low. Silicon is an uncharged compound and is sensitive to leaching. There are many good forms of silica fertilizers available, incidentally there is a small amount of silica available in SuperCal SO4. Could this be one of the reasons why growers report better crop response than with other gypsums?