'Avatar' DVD "Avatar" will be released on DVD on Earth Day -- except it won't be in 3-D ... and there will be no extra features whatsoever.

Producers said extras were intentionally left out of the April 22 release to improve overall picture and sound quality.

As for the DVD's disappointing two dimensions -- a Fox spokesperson said a 3-D release can be expected in the future.

Despite losing Best Picture, James Cameron's little blue alien movie has grossed $730 million domestically ... and is still in the top 10 at the box office.