[Aeraaa]

You dont have to; just as in calling new fire mission with HE rounds, if you want to send smoke, click on the artillery unit in the bobardment screen(this will send you to the hex that was previously bombarded) and instead of using HE rounds, click on the smoke ammo. Voila! Fire mission with smoke rounds next turn. You can even adjust the fire mission, just like with HE rounds(just remember, first click the smoke button and THEN adjust, otherwise you'll do a normal HE fire mission...)