Biomass and radar vegetation index

hi my name is Mamurbek from Uzbekistan i want to find out about biomass related wheat and cotton and corn because i work at space agency of uzbekistan pls dou you know about anything biomass wheat and cotton , corn pls tell me. i try to use sentinel 1 data vv vh result why polygoms aren’t full vegetation
and i calculated RVI 4*vh/(vh +vv ) and i took like this