Qu'un sang impur Abreuve nos sillons!
May tainted blood Water our fields! (I've also seen sillons translated as furrows)
The Marseillaise is not the only violent French revolutionary song. Less well known is the bloodthirsty 'ça ira' ('that shall be' - or that's my translation anyway) which is all about stringing up aristocrats. There is a splendid hags chorus rendition of it in the 1927 film Napoléon. You can just imagine the singers cackling in the front seats before the guillotone.
Les aristocrates, on les pendra!Le despotisme expirera,La liberté triomphera, Ah! ça ira, ça ira, ça ira
We'll string up the aristocrats! Despotism will die, Liberty will triumph, Ah! that shall be, that shall be, that shall be
Stonkingly good stuff :D