Musannaf Ibn Abi Shayba 28:185

Ali ibn Mushir narrated to us, from al-Shaybani, from Abu Awn Muhammad ibn Ubayd Allah al-Thaqafi, who said: Umar ibn al-Khattab imposed upon the Sawad, for every jarib of land reached by water—whether cultivated or uncultivated—one dirham and one qafiz of food. Upon orchards, for every jarib, ten dirhams and ten qafiz of food. Upon clover (alfalfa), for every jarib of land, five dirhams and five qafiz of food. Upon vineyards, for every jarib of land, ten dirhams and ten qafiz. He did not impose anything upon date palms, making them subordinate to the land.