Hi there,
Could be quite wrong, but perhaps it was an attachment to other farming equipment - fitting onto the back of something as in say:
A team of horses (or other animal) would be way off to the right (of say the photo), pulling say a plough, or tiller, and this implement fitted on top of the middle to rear of that plough/tiller. Thus someone sat with their back to the horse and dispersed seeds into the ploughed rows, while the person in charge of the horses and the plough/tiller etc sat facing the horses directing them where to go

Not sure, but I think I heard that type of explanation once when at a museum where the equipment on display came under the heading "dead stock". That is "dead" as opposed to "lives tock" which were the animals on the farm. I remember he also said "deadstock" was only different to his display of the old "capital equipment", as Capital Equipment was very expensive and the "attachments" being of course cheaper, and thus "dead" from a book-keeping point of view.
Hope that helps rather than confuses you all. The museum visit was in the mid 1970's and the chap was displaying his farming family's old equipment. He was very old then and he had worked on the farm all his life, as had his forebears. This was in NSW Australia, in the wheat belt communities.
JM