Stands in my dream just wet lettuce and a blue tractor

Last night I'm walking through rows of lettuce that have faces, not human faces, just the tired look a dog gives you when it knows it's about to rain. A blue tractor follows me slowly, never catching up, and I keep thinking about the way diesel smells when the tank's almost empty. Then I wake up and the real rain is coming down and I can't tell if the dream was warning me or just showing off.