Perhaps

"the clear daylight to/'til the dawn" could possibly be a way of saying all of the time or 24 hours a day.

re "My curse attend you Sweeney" - I think that Sweeney would've been a farm owner or overseer.

re Sergeant-Major/Queen of England - It matters not. It's written or sang in the hope that someone will recruit this guy to the army and free him of his burden - plowing theb rest of his life.