Hi Erin!
While I won't personally recommend feeding
chickens soil fertilizers/amendments, what I will suggest and is something that I do, and it's one of the ingredients in the soil amendment found in the link you provided. I give my chickens kelp, mixed into their layer
feed. Kelp has a wide array of minerals found in the periodic table of elements, often with super stout levels of iodine, and these minerals found in kelp are biologically available for chickens (and people too) to absorb and be assimilated by the body. It's one great way to help ensure your chickens get a more mineral rich diet.
Another route to add minerals to a chickens diet (and here again, people too) is offer them unrefined sea salt. The unrefined sea salts have color, often a sort of light grey or brown color to them, and is a great visual indicator that all the other minerals present in the sea
water that was evaporated to make that sea salt are present in the salt crystals. Sea salts that are snow white in color tend to be missing the naturally occurring levels of sea minerals. Sea salt can be offered to them in a separate container and they will peck and eat it as they so desire. As a side note, I put sea salt my water I drink every day. I don't add so much that it tastes salty or like ocean water, just a little pinch and the flavor is hardly noticeable, but I'm giving my body low doses of a large number of minerals found on the periodic table.
Hope this helps!