For my clover and alfalfa plots I use a fertilizer that is 0-10-10. It is made by the same people that make the alaskin fish fertilizer. It is liquid and it cost about three bucks for a big bottle, can't remember how many ounces are in the bottle though.
Molasas is also another source of potasium for plants, and you could aslo use amaonia for nitrogen. Just do a search for organic fertilzers and you can find all kinds of different ideas.