I may have posted a photo of some seed pots on the back of the tynes on my subsoiling plough. I would have to take a new photo as I am not good at retrieving old ones. Basically it is made from 4" sewerage PVC pipe coming down to a 2" reducer with a end cap cemented on with a hole and another end cap with a centre bolt and numerous varying size holes around the outside so that the chosen size hole lines up with the hole in the other end cap. A curtain wire goes down through the holes and drags along the ground tickling the seed so that it slowly falls through the hole, works well and easily controlled. If I think about it I'll get another photo or two, keep reminding me.