Possibilities:
-- Commodities (agricultural futures or options on futures)
-- Agriculture funds, such as DBA
-- Stock of companies involved with agriculture (growers, processors, transportation, equipment, fertilizer, etc)
-- Buy some farmland yourself, either directly or through a co-op
-- Foreign vs. domestic
Rice trades on the CBOT, among other places. If you're looking for a vehicle more "direct" than a futures contract, it's more difficult, but still possible.