Agnes Denes started doing badass environmental art pieces starting in the 60s, but the one that really stands out is Wheatfield - A Confrontation (1982), which is literally a two-acre field of wheat she planted in downtown Manhattan. She said she wanted to "call people's attention to having to rethink their priorities." Right on, Agnes!
Denes was one of the first artists to produce some really environmental pieces. Even though I love this because I'm all for putting out-of-place things in people's faces to make a point, I have to come back to my "What is Art?" point here. Is every farmer an artist? Is this only "art" because of the context? I know that for me, context is the number one aspect of an art piece. Super important. And here it's obviously affecting the idea hugely.
In my opinion, though Denes may be an artist, this particular work is an activist piece. It's certainly making a statement (which I love) but, though not being able to define art, I'd be hesitant to make any definitive statement about this being it.
(images with permission from Agnes Denes)