The potential seed yield is about 1.8 times greater than the actual maximum yield, and about 7 times greater than the average yield. In the Pacific Northwest of the USA, the bee stocking rate for an established stand of alfalfa is about 40,000 live bees per acre of crop. 7 flowers must have been pollinated to produce them. Average seed yield, however, is only 500 lbs. per acre. Thus, potential seed yield is about 3 times the average.
Numerous factors can reduce potential seed yield in alfalfa.
Lygus bugs, the main flower and seed predator, are controlled with pesticides so that their impact normally accounts for a small percentage of crop loss. Studies of perennial legumes suggest that the plant can respond rapidly to changes in resource levels by increasing or decreasing the rate of development of new racemes and curls. While water is an important resource in this regard, nitrogen has not been demonstrated to limit alfalfa seed yields. Another factor that can reduce seed yields is self-incompatibility, a physiological adaptation that prevents pollen from the same plant from successfully developing into a seed. If spring is cool, flowers may accumulate on racemes before bees are introduced.