Most forage seed doesn’t represent a large percentage of crop input cost, but the advent of reduced-lignin alfalfa, some priced at $6 per pound, should have farmers thinking more seriously about grain drill or seeder calibration. Over the years I’ve seen some huge mistakes made in seeding rates, including planting half as much alfalfa seed as the farmer intended. You probably have a fair idea of your drill or seeder calibration, often via the “by guess and by gosh” method: Put a known weight of seed in the seed box and then find out how many acres it does. However, you can — and should — do better. Alfalfa averages 220,000 seeds per pound, but some seed lots only have 200,000. Seed coatings also have an effect: You’d think that because of the weight of the coating, at a particular setting coated seed would result in fewer seeds per acre. However, coated seed tends to flow faster than uncoated seed, and the amount of coating on seeds varies considerably. When deciding on a seeding rate, be sure to account for the weight of the coating.
Calibration kits are available for most modern grain drills and seeders, but a quick way to determine calibration is to spread a tarp on level ground, then drive over the tarp at normal planting speed and count the seeds in several one square foot areas. For alfalfa, 75-90 seeds/sq. ft. is a seeding rate of 15- 18 lbs/acre. If you have two or more varieties of alfalfa, check the rate for each since there may be significant differences. Determining the seeding rate of alfalfa-grass is somewhat trickier. My suggestion: Premix the alfalfa and grass seed and put it in the seed box, then drive over the tarp and only count the alfalfa seeds in the one foot squares. If you have 65-75 alfalfa seeds/square foot and the grass seed is included at the typical 4-5 lbs/acre, this should result in enough alfalfa seed for high yields plus enough grass seed to increase both yield and forage quality