The rural world underwent extraordinary change. New cereal crops, fruit and vegetables were introduced, as well as new farming techniques. Irrigated crops spread thanks to complex hydraulic technology. Waterwheels and irrigation ditches transported water to the fields. Waterwheels were also used for grinding cereals. The differences between the countryside of al-Andalus and the feudal north were notable. The farmers of al-Andalus, who lived in a monetary economy, grew a wide variety of products. The peasants in the Catalan counties grew wheat, which could be stored to pay their feudal tributes in kind.