Paying closer attention to alfalfa seeding rates would help many growers boost their bottom lines, says Marvin Hall, forage extension specialist with Penn State University Extension.
It’s not uncommon for growers who think they know their seeding rates to be off by several pounds, says Hall. “Studies have shown large differences between seeding rates of different varieties of alfalfa when seeded through the same seeder. Coated seed flowed faster than uncoated seed, which resulted in higher seeding rates than expected.”
With uncoated seed, seeding ranged from 14 to 21 lbs/acre without changing the settings on the seeder, according to the studies he cites. “While this range in seeding rates does surround the normally recommended alfalfa seeding rate (15-18 lbs/acre), the variation can be very expensive. If a farmer thought he was seeding 15, but was actually seeding 20 lbs/acre, the additional cost per acre for seed would be substantial.”
Differences in variety seeding rates are attributed to small variations in seed size and shape. “It is a general rule of thumb that a pound of alfalfa contains 220,000 seeds. But studies have shown a range from 196,000 to 224,000 seeds/pound. Some seeds were slightly rounder and flowed through the metering device faster than other varieties. Recommended alfalfa seeding rates will normally result in 75-90 seeds/sq. ft.” In reality, the observed range in seeding rates was from 70-105 seeds/sq. ft., he says.
Seeder calibration is an important consideration when growers switch alfalfa varieties. Hall recommends driving the seeder over a tarp spread on the ground and counting the seeds that are dropped in a couple of square foot areas on the tarp. Seeders that drop 75-90 seeds/sq. ft. are planting at recommended rates. “Seeders should also be calibrated annually before starting to seed, since slightly worn seed metering devices on the seeders can cause large changes in alfalfa seeding rate.”