Amr relates from al-Hasan (may Allah have mercy on him) that the Messenger of Allah (peace and blessings be upon him) "prescribed zakah only on ten things." Then he mentioned them, and among them he mentioned sult (a kind of barley) and did not mention sorghum (dhurah).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7481