If you are seeding cover crops, or any other seeding (pasture, buffers, CRP, etc.), remember that seeding rates MUST be calculated in pure live seed. Seeding rates are determined based on the number of live seeds per square foot to achieve a specific plant density. PLS is the percentage of seed that has the potential to germinate. The use of PLS guarantees that the same amount of viable seed per acre is planted even though different seed lots will have varying quality.
To calculate PLS, you need to know the % total germination and the % purity. This information should be on the seed tag. The basic formula to calculate PLS is:
Percent (%) Purity x Percent(%) Total Germination (germination + dormant seed)/100 = % PLS
As an example, if your seed tag indicates that the lot has 98.75% purity and a total germination of 93% (germination 88% + dormant seed 5%), then the calculation would be:
98.75 x 93/100=91.83% PLS
If you needed to seed cover crop at 55 pounds per acre, and only had 91.83% PLS, then you would be seeding 45.9 pounds of good, viable seed.
A rye cover crop PLS calculator can be utilized by clicking here. You can also compare the cost of purchasing rye vs. growing/harvesting your own. The calculator can be used for other types of seed, but the bushel calculations will be wrong.
If you are receiving money from the Iowa Department of Agriculture for contour buffer strips (also known as the Buffer Initiative) or cover crops, we require that you bring in seed tags to show that you seeded at the proper rate based on PLS. It is recommended, but not required, that you bring in your seed tags for all other programs (CRP, EQIP, and CSP).