Mike if you picture the scoop in the MG boxes, it has a small scoop on one end, I think labled tsp. I use 2 of these in a two liter soda bottle with holes drilled in the cover for fertilizer delivery . I do this every week end with no bad results.
Now part of the issue is how much of this juice do you now put in the pot, half a bottle in one pot might be no benificial to your tree, I don't have a method I can describe per se as to how much I use per tree, but I water first, then go around and fertilize as to what I feel the size of the pot would require.
If you use a free draining soil it's been said by many, that know more about it than I do, that the tree uses what it needs, and root burning isn't on the list of horrors you will do to your tree, I suppose if you dump the stuff crystal form on the soil and water it in a bit, it could be dicey.
If you are watering twice a day like many of us are in this heat, w/ a good bonsai soil, I feel this is NOT an issue to worry about.