You're all overthinking it. They dumped their kitchen waste in the fields, and it happened to contain broken pottery too. It's the same for other archeological sites all over, many are waste dumps that contain interesting objects.
If you're reading about the use of pottery in soil, it does not matter what the people intended—at least, not as a primary concern. It is easy to read intention into headlines though.
> These discoveries suggest that the area’s Indigenous farmers may have dumped their household waste and the remnants of fires onto their fields, using them as compost