I do not have any hard data, because I have been gardening for so many years and most of my stuff I have just picked up. Last year I was watching The Miracle Garden on 3ABN with Ian Jones (now off the air) and he recommended lots of Epsom Salts
for yellowing leaves, which was a problem I was having at that time.
This year I made sure to add extra Epsom Salts
when I built my soil, but I still had some yellowing of leaves. With all the liver/gall bladder flushes I have been doing and reading about the major importance of magnesium in our diet and how most of us are deficient, I added even extra Epsom Salts
to the garden a few days ago. We have had some rain, and the plants are a richer, deeper green and they have absolutely taken off in a growth spurt. I also side dressed with compost, so I'm sure that helped as well.
I do not know if magnesium can be seriously overdone in the garden. I suppose the plants will just take up what they need. I do not know if it will make the soil too alkaline.
Would love to hear from others on this subject. Thanks.