Thanks Sye. DE came up in a few articles but not one particular study concentrated on that. However there are studies such as one in India that did end up mentioning this:
A few studies have shown that application of DE can be beneficial for plants as a source of Si. Diatomaceous earth is formed by diatom frustules composed of amorphous Si (BSi) that is easily soluble compared to the other silicates common in soils (Fraysse et al., 2009). Rizwan et al. (2012) showed that DE application might reduce the toxicity of Cd in wheat and attributed this effect to Si, which induced a decrease in available Cd in the soil.
I'm sure there may be a way to apply it but it didn't say in that article. The chart below shows the composition of diatomaceous earth.
You can see over half of it contains silicon dioxide. It still needs to be broken down into MSA which is most likely why you wouldn't notice results with short term use. The amount of silicon dioxide in the soil influences the concentration of the MSA. The study above says DE is
easily soluble compared to the other silicates, which could be potassium silicate which is not that soluble.