Without knowing what it is it is difficult to say. Is it poultry manure or horse or cow? With most manures you just apply a layer around and out to the drip line maybe about an inch deep but, don't put it on top of the root flare. It won't burn the root flare but in time will cover it up. The big root flare roots are not feeder roots. The flare roots are what the feeder roots are attached to. Feeder roots are small, tiny, and are found slightly below the soil surface and downward. Straight dried manures are fairly mild except for chicken manure which is a little hotter but by watering in the layer of manure it dilutes it and stops it from burning the feeder roots. Feeder roots extend out to the drip line and maybe a little further. On your tree, I would layer the manure in a radius of about 2 feet.