Farmer's Bulletin No. 2191, TREFOIL PRODUCTION FOR PASTURE AND HAY, was released by the U.S. Department of Agriculture in July, 1967. This publication noted that acreages of trefoil in the U.S. increased from 770,000 in 1957 to over 2 million acres in 1967. This bulletin is an excellent guide to kinds of trefoils, to the different varieties available, and to general production practices in obtaining stands and in managing this legume. It is stated in the bulletin that birdsfoot trefoil is not recommended south of a line drawn from the Nebraska-Kansas border to the east coast, except at higher elevations. (The very northern tip of Kentucky is about 70 miles south of the Nebraska-Kansas line.)
Sigafus, Roy E.; Templeton, W. C. Jr.; Taylor, T. H.; and Wyles, J. W., "Some Observations and Comments on Birdsfoot Trefoil" (1972). Agronomy Notes. 125.