Would sowing annual rye grass around in ground fig trees in late winter take the excess nitrogen out of the soil and tie it up to prevent early leafing out? Also what about planting crimson clover around base in summer to fix nitrogen?One more thing how about sowing turbo radishes around in ground trees in fall to drill holes in the ground, the radishes will rot in the ground during winter leaving holes for nutrients water and air to get to the roots

My guess is that radishes will be fine but anything else will compete with the tree for nutrients.  If you grew clover elsewhere and mulched the tree with it in the fall that's a different story  :)