Yup, that's the pic I recall . . . .
I use a hand full of a 20-10-10, sprinkled / spread out around the base. It has ESN with it, from the dealer.
I do it to all my trees about once a month (april - Nov). It really helps. As much as the multch and water.
Don't do it, if you don't water though. If I didn't water, I'd only do it in the rainy months of spring and fall. You will end up with some greening up of the grass around the multch areas.
I also us around 1500 lbs total, 20-10-10 on the lawn / trees split up 3 applications.
It really thickens up the grass and chokes out the broadleaf's - Again, I would limit the application to the rainy early spring / then fall. Last fall, it was so dry - I skipped the application. The grass was green, but dormate.