If I had found that many Native American Indian Artifacts in such a short time and there are no more visible, I would pay the farmer to plow the field again, then ask him to wait until after the next rain and a day or two of searching for more artifacts before he plants. What a haul! Is it possible that the site was what we call here an Indian Blacksmith Shop where tools, arrowheads and spearheads were made? There was one across the river from my brother-in-laws sister's home in Sevier County, Tennessee and every time they plowed the field there, hundreds of arrowheads and a few spearheads could be found. When the field was plowed, the next day some folks would arrive at the site a couple of hours before daylight to be the first one's out there searching. The farmer let this go on for years but then he sold the land and the new owners posted everything. You can still occasionally find arrowheads and spearheads in the river and along it's banks on that side of the river.
Frank