Yeah, we need Poloniex.
Right now, according to suprnova -
http://prntscr.com/8uqo5q , we can mine about 1.44 soil/MH per day.
Ethereum - 0.07 eth/MH per day.
Soil mining is about 20 times easier that Ethereum.
Ethereum price is 0.0019 BTC.
So, soil must have price of about 0.0019 / 20 = 0.000095 BTC (let's round that to 0.0001) for its mining to be as profitable as Ethereum's.
I don't know why I've calculated all that

just for curiosity.