Pure Live Seed (PLS) is, basically, the portion of good, viable seed. It is a measure of the seed that is alive and able to sprout into plants.
To better understand the concept of Pure Live Seed, it is helpful to break down the term. “Pure” and “live” are both words that describe the seed:
To determine pure seed, the first step to is to separate the seeds from the not seeds. The things that are not seeds, such as leaves and stems, are termed inert matter and are set aside from all the seed in the sample. The percent of the lot that is inert is shown on seed tags. The second step is separating and counting each type of seed in a sample. There will often be seed of more than one species because other seeds were harvested with the main crop. The percent of other crop and weeds are both recorded on the seed tag. Anything that isn’t inert matter, other crop, or weeds is the pure seed, which is shown on the seed tag as purity.
The pure seed is then tested for the ability to germinate. There are two types of germination considered in PLS: seed that germinates quickly and seed that is dormant. The seed that cannot germinate is considered dead, while the seed that does germinate is considered live seed.
Calculating Pure Live Seed
Once the pure and live portions of the seed have been determined, the percentage of pure seed is multiplied by the percentage of that seed that is live. This results in the Pure Live Seed percentage. If PLS was a math problem, it would look like this:
PLS % = Purity % x Germination %
Or, if the germination is given as germination and dormant, the equation could be written like this:
PLS % = Purity % x (Germination % + Dormant %)
Reading a Seed Tag
To look at a real-world example, below is a seed tag.
Above is an example of a seed tag. The purity, inert matter, other crop, and weed seed is in the center box. The germination test results are listed on the right-hand side of the tag, and just below this is the PLS rate. The PLS rate was calculated by multiplying the purity of 90% by the total germination of 80%, resulting in a PLS rate of 72%.
In other words, in a 100-pound bag, there are 90 pounds of Big Bluestem seed and, of that pure seed, 80% can germinate This means that 72 pounds of Big Bluestem seed in the 100 pound bag is capable of germinating. Said another way, there are 72 Pure Live Seed pounds. In this 100-pound bag, there are also 0.5 pounds of weeds, 1.5 pounds of other crop, and 8 pounds of inert material.