And then back to silicon please.....
Seems as if I triggered a discussion here that may lead us somewhere
I have skimmed through some papers on the issue and found that often calcium silicate(CaSiO3) is used as silicon source. Having worked with silicate science for 30years now, I wonder whether calcium silicate actually is a good source of silicon, just as I wonder whether the so-called soluble silicates are any good at all
The reason for my doubts are based on the following: for silicon to be absorbed by plants, it must be as soluble monosilicic acid that is slightly soluble, some ppm. The problem with the silicates is that the silicon is present as anions, e.g. as SiO3^2- . In acid environments, these can equilibrate with monosilicic acid (Si(OH)4) but under any circumstance, monosilicic acid is a shortlived compound due to polymerization. And the polymers are not that easily absorbed by the plants.:wink:
http://pubs.acs.org/doi/abs/10.1021/ja01637a017
This link
http://www.firt.org/sites/default/files/Scarbrough_Silica_in_Plant_Nutrition_presentation.pdf
sums up quite a few of the observations, although it is a commercial marketing presentation. The product in question here is probably a slag.
Then, my two cents on why I do not believe in soluble silicate solutions. Most soluble silica solutions a.k.a. Waterglass, e.g. Potassium waterglass has an alkali/silica ratio that is much lower than the required ratio of 1. This simply implies that silicon is not present as monomeric silica, but as polymers. And the polymers do not easily get absorbed. And if the ratio is correct, delivery as a solution probably results in a polymerization anyway:evil:
Using these solutions may well have positive effects, sealing/strengthening the epidermis with a silica glass, but it does not get absorbed by the roots.
So to sum up, silicon nutrition is not straight forward. What can be done is to use soluble silica(not silicates). This is typically amorphous structures with high surface area. Some alternatives have been mentioned earlier in this thread. Perlite has been mentioned, I am uncertain how effective it is but perhaps
Silicon fertilizing is done at a big scale in the rice-fields of the far east, and a lot of research is being done on the issue in countries like Japan. Of course, rice is a silicon intensive crop, and the fields get easily depleted. Some modern agricultural practises add to the problem. One example is that while the rice hulls/straw used to be burnt on field in slow burning heaps(low temperature), nowadays the remains tend to be carried away and burnt in a more effective way, producing heat etc. The problem is that even if the ash would be brought back on the rice field, the silicon would have become unavailable due to the high firing temperature. It has turned out that the old fashioned stinky heaps of slow burning rice remains was perfect to liberate the silicon which was brought back onto the fields.
this does of course not happen anymore and if it does it does not contribute significantly to soluble silicon, and the fields get depleted. Composting is not an effective way either it seems.:rollhappy:
So, back to start; my original question was: Why do we fertilize with phosphorous, sulfur, calcium, magnesium etc. but not with silicon although silicon is just as abundant in the plants as the rest? And as we know, the substrates commonly used are not particularly rich in soluble silicon either?
oke
Btw. I have started fertilizing with microsilica and "think" I see notable improvements. I will never be able to prove it though, as I also changed other things more or less simultaneously.:evil::evil::evil::evil:
