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Adjust Actual Seeding Rates Based on PLS (Pure Live Seed)
Basing seeding rates on pounds of pure live seed (PLS) assumes every seed is viable and capable of producing an established plant. A seed lot with 100% germination and 100% purity has a PLS index of 1.0. The rate of seeding or the actual pounds of bagged seed planted must be adjusted upward for seed lots with a PLS index of less than 1.0. Seeding rates of legumes frequently are not adjusted if PLS is greater than 90%.
To determine the adjusted seeding rate for each species or seedlot of a given germination and purity percentage (given on seed tag) follow the steps below:
Step 1: (% germination X % purity)/10,000 = PLS index
Step 2: PLS seeding rate � PLS index = lb bagged seed/acre
If hard seed (seed that is viable but has an impervious seed coat) content of legumes is greater than 20%, scarification should be considered. Scarification is the nicking of the seed coat to allow moisture to penetrate. Most alfalfa seed grown in the Pacific Northwest has less than 15% hard seed, but locally grown seed may have up to 50% hard seed depending on the environmental conditions grown under.
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