Well
That’s when you apply 5kg/square metre, which is rather a lot!!
My hunch is that the application of the rock dust means that all the trace elements needed by worms, soil bacteria, fungi and plants become more bioavailable, everything ticks over more effectively.
Whether the analytical tools exist yet to be able to measure concentrations of optimally available trace elements in soil I don’t know, but the only way to really understand this is to correlate long-term growth/yield measurements with the corresponding levels of trace element bioavailability.
One suspects that the next big advance in the holistic understanding of soil productivity will be in this arena, but it’s highly complex, as you have to overlay the variables of climate, soil type and precipitation levels when interpreting data.