Farmers spreading crushed glass on their crops

I read the article because it is so promising but one thing I was confused about is they kept that they kept talking about silicon in the glass but silicon is present as SiO2 and SiO4 in glass so my question is when does the silicon comes out of the silicate structure or is it the benefits of the silicate structure that they are attributing to silicon. Also as the previous comment says "why not sand" instead of glass.

I find it a bit strange that they regard glass as a waste product which it is not. Furthermore, if the working component is silicon then you can just as well use sand instead of glass.

Tell me more, serious question, how is glass turned into silicon ?