In the foreground, a peasant, wearing leggings and a hat, plows with an ox. Above that, to the left, three peasants are working with the vines, probably pruning and re-tying them. Above and two the right, a peasant with a sack is doing something to a field. I suspect (but do not know) that he’s spreading manure on a field deliberately left fallow.
It was fairly common to use a three-field system of crop rotation http://www.uh.edu/engines/epi26.htm. One field was planted with wheat or rye in the fall, for human consumption. A second field was used in spring to raise peas, beans, and lentils for human use, and oats and barley for the horses. The third field is allowed to lie fallow, and rest. It would be plowed, working aged manure into the soil, and any spontaneous weeds and grasses could be used for grazing, resulting in more manure to be plowed under a second time.
The field planted with beans, and lentils, with legumes in summer could be re-used the next winter for winter wheat or rye, because legumes, as nitrogen fixers, enrich the soil. Each year, the field used for a specific crop rotated among the three fields.
I suspect the fellow with a sack is spreading manure that will be plowed under while the field lies fallow. The third field, off to the right, looks as if it’s already been planted. Across from it, on the top left, there’s a shepherd with his sheep and dog; he appears to be hurriedly covered, perhaps hoping to avoid the storm that appears hovering in the sky above.