A farmer ends the day by walking through his fields, and what he sees is bare earth. The poem is only three lines long, but its last line changes how we read the rest. After the plain setting of "home and barn in the evening," the speaker calls the dirt "a magnificent supper."
That word choice is the heart of it. The fields are not just ground the farmer works on; they are what feeds him, and perhaps what he feeds too. Plowed or harvested land, "all in dirt," might look empty to an outsider, but he finds it rich and satisfying. The judgment seems to be a happy one, full of quiet pride and contentment.
The mood is calm and settled, like the end of a long day. The short lines and simple wording match the farmer's steady, unshowy relationship with the land, and the single grand word "magnificent" lands all the more strongly for it.