When Andy and Barney stake out Sam Becker's farm and spot Sam driving his tractor in a field, Barney muses that Sam is planting marijuana. Andy doubts it is marijuana but states that Sam is definitely planting something. The goof is that Sam is using his tractor to pull a set of soil cultivation disks. If Sam were actually planting something, he would be pulling a planter implement of some sort and not a set of disks. Also, the disks are just rolling noisily across the top of the ground and not cutting into the soil as would be required for soil cultivation.