When it comes to minerals, over 90% of what goes in the front end of a cow comes out the back end. For some minerals it is nearly 99% comes out the back. It doesn't matter whether the mineral is coming from the grass, supplemental feed, or a mineral block. Most of it goes back out on the ground. Now, here's where it gets tricky. In continuoulsy grazed pastures, half to two thirds ofthe manure is usually deposited within a couple hundred feet of water and shade. That means even though the sh-- is all coming back on the pasture, it isn't being put where it will do you any good.
Short grazing periods with high stock density usually result in much more uniform manure distribution and can cut way down on fertilizer needs just by making the natural nutrient cycle turn more efficiently. One of the key factors is getting the cattle closer to water (which is what you usually get if you install a MiG grazing cell). This is especially true in hot, humid areas. Even without subdivision fence just making more water points on the landscape helps pasture utilization and manure distribution.
Bottom line is if the field is used only for pasture and only grazed effectively, the fertility will get to an acceptable level and little if any fertilizer is needed after that.