Why is alfalfa one of Arizona's biggest crops?

Children in Arizona are often taught the 5 Cs that traditionally made up the state's economy: Cattle, Citrus, Climate, Copper and Cotton. As the state of our water supply changes, what's happening to those longtime industries? Tapped begins a mini-series looking to answer that question with an episode on agriculture, the economic sector that includes three of those five Cs. Is the industry that accounts 72% of the state's water consumption using its supply of water wisely?