Some rusty parts on the tractor and a bit of structure to the surfact would make this image even better. Maybe some very subtle and blurred reflections on some metal parts (like the weels) would increase the looks of this image. But don't use chrome weels, a little rusty metal works better for this image I think. Also the horizon shines through too much. Maybe you can hide it with a little terrain. (not too high though, I think a mountain wouldn't look good) Great colors on the trees and the ground. with a little tweaking this could be a winner.

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