Not to jump on the bandwagon, but the overdone vignette was the first thing that jumped out at me too. Bear in mind that these are only our opinions, and I get what you were trying to do with the Grapes of Wrath feel, but I think Derrel nailed it when he wrote that it's a very heavy effect. I think a light vignette works here, but one this dark doesn't feel natural.
One effect of vignetting (besides the old-timey feel) is to darken the periphery in order to bring the eye towards the center of the image, and I think in this case that does this shot a disservice. The vignette does effectively draw my eye to the centered silo. However, what I like most about this shot is that you have some great converging lines going right-to-left. The tops of the silos, the apex of the barn roof, and the rear top corner of the truck's trailer are fairly well aligned; ditto for the bottoms of those four. Without the vignette drawing attention away from the truck and the large silo (by the way, I like the most dominant feature - the large silo - being positioned off center), those lines would really work to make the four items work well together in a comprehensive scene.