If my Tideturner controls Ravenbloom Conservatory and trades with Lonely Poro, after that my opponent moves Scuttle Crab to attack the empty battlefield. I use Ride the Wind to move my Ravenbloom Student there. Will I be able to use the effect of the battlefield?

No, you won't be able to use Ravenbloom Conservatory's ability.

Here's why: After Tideturner dies in combat and the battlefield is empty, you lose control of Ravenbloom Conservatory in the next cleanup (Rule 187.4.c — no units + Open State). When your opponent later moves Scuttle Crab there, the battlefield becomes Contested but has no Controller. Even after you Ride the Wind your Ravenbloom Student there during the ensuing Showdown, the battlefield remains Contested and uncontrolled — control is only established at the end of a Showdown (Rule 187.4).

Since "you" in a battlefield's ability refers to its Controller (Rule 187.6.c), and there is no Controller during the Showdown, "you" refers to no one. The trigger condition "When you defend here" cannot be met by either player. Same ruling as FAQ #8647 which covers this exact interaction with Ravenbloom Conservatory.