In just four lines, the speaker describes planting, but what goes into the ground isn't only seed. It's "our business, our absence, ourselves." The list moves from the practical to the personal: first the work of farming, then the time we spend away from everything else, and finally our own selves. Farming here seems to mean giving yourself over to the land, not just using it.
The last two lines turn quiet and strange. After all that burying, what's left above ground is "nothing but light / in the evening fields." That could suggest the farmers have vanished into their work, or that something calm and almost holy remains once the labor is done. The mood is hushed, a little wistful, and oddly peaceful. The speaker doesn't sound sad about disappearing. Judging by the imagery, there's a sense of acceptance, even beauty, in being absorbed into the land and leaving only the glow of dusk behind.