Yield, yield components, and forage nutritive value of alfalfa as affected by seeding rate under irrigated conditions

Persistence is a critical component of alfalfa (Medicago sativa L.) crop yield. Our objective was to determine the effect of seeding rate on alfalfa persistence, yield, and yield components and how they evolved over time in irrigated areas with long growing seasons. Two alfalfa cultivars were seeded at four seeding rates (10, 20, 30, and 40 kg ha(-1)), in three consecutive experiments, and evaluated over a 3-yr period to provide total data for nine location years. Seed rates of 10 kg ha(-1) [8.75 kg ha(-1) of pure live seed (PLS)] produced total 3-yr dry matter (DM) yields of between 50.8 and 58.9 Mg ha(-1). Seed rates only affected total 3-yr DM yields in one of the three experiments. The mean number of shoots per m(-2) was 488 and this was not affected by seed rates. The effect of seed density on mean shoot weight depended on the experiment. The annual average crude protein (CP) concentration varied from 159 g kg(-1) to 224 g kg(-1) while the leaf to stem ratio varied from 0.87 to 1.17. The results suggest that CP and leaf to stem ratios (LSR) were either little influenced or not influenced by seed density. The DM yields and yield components indicate that 8.75 kg ha(-1) of PLS could be sufficient to ensure adequate DM production. Results also suggest that in a Mediterranean climate in which sprinkler irrigation is applied, there is little justification for high seeding rates under good establishment conditions.