could i system be implemented that players captain and above that is a part of a specific nation can donate gold to treasury.

Eg: A Scotland player has 20,000,000 so he/she could deposit it into the nations treasury.

in this way the nations treaury could grow.pls don't misinterpret the sending payments because that would still be for dukes and higher.

just any player once captain or higher in rank can add there gold own gold on hand into nation treasury

This was brought up earlier and was disapproved as this would result in hiding a players gold in a nation's treasury. A alternative could be that you could raise your country's taxes.

Yes, this was brought up and rejected but there is a way to do it- just raise taxes for about a month and you will steadily grow your treasury.