synthetic free herbicide??

Hi guys, so happy to have this resource! I am working in the tropics where we have about the most stubborn weeds I can imagine. Does anyone know of a good plant based herbicide. It doesn't really have to be plant based but something natural and free of synthetic chemicals. I have two purposes here. On occasion I have to clear out an old and overgrown pasture to plant new seed and other times I have to maintain my road so the plants don't deteriorate it. I have heard of the Nitrogen overdose method but I doubt it would work for the roads as it makes the dirt better in the end and I need a bit of a more permanent solution. However if thats the best natural option there is I can just keep applying for the roads...have yet to try it but will be doing so soon.

I lay glass or clear plastic over weeds areas that I want plant free.   After a few days in hot sun, they burn off and don't come back the rest of the year.

This works great for the small areas in front of my door step, paths to my gardens, etc.   It would be to time consuming otherwise.

If I had to clear a large area, I would use goats.