yes you can, I have done it countless times without any issue's on several different properties!
as long as the soil PH is correct and you add nutrients as needed, you can plant same crop yr after yr
farmers do it all the time on corn and soybeans as proof!
if your worried about any issue's
just use a different type of turnip/rape/brassicia
there are tons of varieties and as such you will NOT be planting the same make up plant again!
now on a side note
your NOT planning to MIX the two seeds into one growing plot are you??
as that really won't work out well
as turnips will NOT bneed to be mowed, where clover will be!
and most times turnips, brassicia/rape and likes, are planted in the fall and NOT the spring time too, so?
just saying!
don't plant these types of seeds in spring time, or you will just have rotting away turnips come late early summer! and a very un attractive plot for deer hunting in fall!