I don't suppose a farm of 290 acres would all be arable, and wouldn't all be ploughed or harvested at the same time. There would be hedges, ditches and access roads that would take some acreage. They would have horses for ploughing, and cattle and sheep for milk, meat and fertiliser, so some of that acreage would be for meadow and pasture. Some portion would be fallow each year. The cropped area would also be divided in two, with spring and autumn crops, which would also spread out the workload.
It was still very hard work, but 14 labourers could handle about 20 acres each.