In the United States alfalfa-growing has gone hand in hand with the development of irrigation. Alfalfa did not become an important crop in the country until after irrigation began to be practised in the West. Very soon after the pioneers reached Utah, alfalfa was brought to the state where it found conditions well suited to its growth. Wherever settlement extended alfalfa was raised as one of the most important crops, and finally from the West it has spread eastward into the humid parts of the country.
Harris, F. S. and Pittman, D. W., "Bulletin No. 180 - The Irrigation of Alfalfa" (1921). UAES Bulletins. Paper 146.