I picked up some huge bags of feathers for nitrogen in my garden bed from a down factory. The bags were 6ft long. I emptied them into my garden beds and covered them with soil and by the next year there was no sign of them. They are not the easiest thing to contain and get covered up but I intend to do it again. They have a very high nitrogen content. I think they will be the perfect addition to the leaves I'm sheet composting. Anyone else try feathers?