It's tradition (at least in North Dakota, where both my parents are from) that when a farmer retires, he gives away all the plowshares from his plow to friends and family.

A plowshare is that nasty, slightly curved steel blade that churns up the sod and dirt to get the ground ready for planting.

It's a very abstract landscape (reminiscent of North Dakota...all flat) to pay tribute to the toil of farming.