Thanks for the detailed reply.
I don't like to use cement, so will avoid it.
Yes, seedball is small and I have to make it bigger next time. The way I make it is, first I will put a handful of seeds make them slightly wet and then will add powdered and sieved soil and mix it with thoroughly, keep adding little bit of water and soil and each time mixing, so each seed gets a coat of soil. If I have to make it bigger, this process has to be repeated many times. Last time, I made 0.5Kgs of sesame seedballs in 45 minutes. Completely mixing seeds with soil and making one by one will take a long time, not sustainable...If I can make them retain moisture after one irrigation, that will be excellent, so coir, may be an option, but how to add this in the procedure which I use is a question?
Mulching one layer under and one layer above also is a workable solution, has to try it out.
Thank you so much for these thinking, as people say, 'devil is in details' we have to observe and keep correcting and it should work for the local situation, that is the challenge in natural farming.