Ah, I see you are much farther along with your garden than I thought. Wonderful!
As far as good soil amendments, my favorite is alfalfa pellets which might be available to you. They are used as horse food here and come in 50lb. bags. Arabia is famous for its horses, right? They will also introduce the micro-organisms you are needing for healthy soil. If you can't get the pellets, you can get it from the horse - horse manure is great as an amendment. But you do need to let it compost for a little time before you put it directly on plants as it will have a lot of ammonia compounds in it that can burn your foliage.
The papayas do grow naturally with a hollow stem like that. They need a lot of water and may have expired due to the high temperatures. Again, you might be successful if you grow them under shade cloth, and mulch the root zone thickly with organic material.
