Calculating Seed Mixtures

All NRCS recommendations for calculating seed mixtures are expressed in pounds of Pure Live Seed (PLS). PLS is defined as the percentage of pure seed that will germinate expressed as a percentage of a given weight of seed and is a means of expressing seed quality. It provides a common basis for comparing seed lots that differ in purity and germination. It is also used to adjust seeding rates to achieve the desired stand. Seeding rates based on a PLS basis, will insure that the same amount of viable seed per acre will be planted even though quality of different seed lots and total amount of material (bulk) seeded per acre may vary considerably. The basic formula to calculate PLS is:

PLS = (percent purity X percent germination) / 100

The information necessary to complete this calculation is found on the seed tag or the Seed Analysis Report.An example of how to calculate PLS is:

'Goldar' bluebunch wheatgrass: Seed tag indicates this lot has 99.01 percent purity and 87 percent germination. The calculation would be:

PLS = (99.01 X 87) / 100
PLS = 86.14 percent

Once PLS is determined for the lot of seed, it can be used to compare the seed costs of two different priced lots of seed. For example, Dealer X has the same variety of alfalfa as Dealer Y, but it is $0.20 cheaper than Dealer Y’s seed. Which is a better deal? The way to calculate this is to use the following formula:

Price per pound (PLS) = price per pound bulk / percent PLS

Dealer Y’s Alfalfa seed is selling for $.90 per pound. The seed analysis report lists the purity as 99.5% and the germination as 90.0 percent. Dealer X’s Alfalfa seed is selling for $.70 per pound. The seed analysis report lists the purity as 93.0 percent and the germination as 60.0 percent. Using this information, the actual price per pound of Pure Live Seed is:

Dealer Y:
Bulk price per pound (PLS) = $.90 / 0.895
Price per pound (PLS) = $1.01

Dealer X;
Bulk price per pound (PLS) = $.70 / 0.558
Price per pound (PLS) = $1.25

From these calculations, it is easy to see that the posted price is not always the least price or the best buy.

< Back to Reading Seed Packaging Labels and Calculating Seed Mixtures

Last Modified: 07/05/2007