Effect of seeding rate on alfalfa stand longevity

Alfalfa (Medicago sativa L.) seeding rates greatly affect the number of surviving plants after 1 yr. The objective of this research was to determine what effect seeding rate has on alfalfa stand density two or more years after seeding. Different alfalfa cultivars were spring-seeded at rates ranging from 3 to 27 kg ha(-1) pure live seed into tilled seedbeds in Missouri and Pennsylvania to provide eight location-years of data. After the seeding year, herbage was removed four or five times each year. Stand densities were determined one to three and five to eight months after planting (MAP) and annually in the spring thereafter for up to 7 yr after planting. Increasing seeding rates resulted in near linear increases in plant densities from 100 to 800 plants m(-2) within 3 MAP. Higher plant densities experienced eight times higher plant deaths the first year after planting compared with lower plant densities. At all eight location-years of this research, the period 24 to 36 MAP had the least amount of plant deaths regardless of seeding rate. Higher plant densities associated with seeding rates greater than 17 kg ha(-1) did not persist beyond 6 MAP. Seeding rates of 10 and 17 kg ha(-1) had similar plant densities by 24 MAP in 75% of the location-years although further reductions in seeding rate reduced plant density for up to 4 yr after planting. Seeding rates greater or slightly less than those recommended have little to no effect on the life expectancy of an alfalfa stand.