This is a hay rake.
After cutting the alfalfa, someone comes along with this and collects it all into piles. The piles are then thrown on to a hay wagon by someone with a pitchfork. With a full load, the hay wagon pulls up beside the barn where a hatch has opened up. A track runs along the top of the barn. A large claw, similar to what you'd see grabbing stuffed animals in the claw machine at the arcade, would come along the track, out the hatch, drop down to grab the alfalfa off the hay wagon, hoist it back up, go back inside, and drop it in a pile. Later, the alfalfa would be fed to the horses and cows. Alfalfa is different from hay in that it needed more protecting from the elements. Thus, the need to get that stuff inside.
But, back to the hay rake.
Operating it was a two man job. One person would drive the tractor pulling the hay rake and another would perch on that seat in the middle of the rake to raise and lower the teeth. In the pictures above the teeth are raised. Below, you can see a foot rest and the lever being held down by a hook. Push it down and to the side to release it. When the lever comes up, the tips of the teeth drop down on the ground to collect whatever loose material you come across. Push the lever back down to drop the load, then drop the teeth again to keep going and make more piles.
So it's a two man job just to make piles of alfalfa. You've got two or three more collecting your piles, and probably more at the barn controlling the horses that run the big hook on a track that I mentioned before.
Have I mentioned I love my desk job?