The Russian serfs were pretty much slaves, who belonged to whoever owned the land so when the country needed new soldiers they had to go over the nobility to get their common recruits.

Another relevant thing about the Russian army is that it was essentially army for life. As a drafted serf you had to serve for 25 years without much opportunity for promotion, since officer ranks were noble positions. And if you survived and returned to your old home town not only would you be a stranger to everyone, you were, as a veteran, also freed from serfdom so you had no place back there. When a member of their community received a draft order the whole village would have a big farewell party that essentially amounted to a funeral celebration.

And then I've also got a relevant anecdote for your quota question, taken from Adam Zamoyski's 1812, which I'm reading right now and can highly recommend:

When Tsar Alexander went back to Moscow from his army during their initial retreat from the Napoleonic invasion he took part in a reception for local noblemen and merchants, where he held a glorious speech about the need to make sacrifices to defend the fatherland.
The aristocracy then started to discuss whether it was enough to allocate every 25^th serf to the Tsar's service when someone suggested every 10^th , which the congregation accepted with many cheers. Furthermore, they also agreed to donate three million ruble, which the merchants joined with eight of their own.