The Asrelia spell Bounty increases the amount of food in a collection of it by 10%, permanently, without any limit, and without any restriction on further casting. Since compound interest is the most powerful force in the universe, this means that it takes only a moderate amount of Rune Points to generate arbitrarily high amounts of food over time. You certainly don’t have to farm or bothersome stuff like that. Your army can be easily supplied on the march. You can sell truly vast amounts of grain.