Utah Agricultural Experiment Staion Bulletin
From a practical standpoint, the culture to use is the one that gives the greatest net return. The study indicates that planting alfalfa for seed production in 24-inch rows at a rate of 1.5 pounds of seed per acre and thinning in the fall of the year after planting is best. For example, a field planted in the spring of 1963 should be thinned in the fall of 1964. Cutting out approximately every other foot within the row seems advisable. While there appears to be considerable latitude in the extent of thinning, weed problems are encountered if the stand is thinned much more than this.
Pedersen, M. W., and W. P. Nye. 1962. Alfalfa Seed Production Studies. Utah State Univ. Agr. Exp. Sta. Bull. 436, 22p.