What Is Pure Live Seed (PLS), and Why CRP Paperwork Needs It

Your conservation plan lists a seeding rate in PLS per acre. The tag stapled to the bag lists purity and germination, and nothing on it says PLS.

Pure live seed, or PLS, is the share of a bag that is the species you ordered and is able to germinate into a seedling [2]. Everything else in the bag is chaff, dirt, broken seed, weed seed, or another crop. On a lot at 85 percent purity and 75 percent germination, that everything else is more than a third of the bag weight [2].

What Does Pure Live Seed Actually Measure?

Seed bought from a vendor is bulk seed. Bulk seed holds mostly live seed of the species named on the tag, along with broken seed, weed seed, and inert material such as twigs and hulls that will not grow [2].

PLS strips that filler out of the number. Multiply the purity percentage by the germination percentage, then divide by 100 [4]. The 85 and 75 lot above comes out at 63.75 percent PLS [2].

The figure is rarely printed on a label, but every input it needs is [2]. It gives you one number for comparing two lots that differ in cleanliness and in viability.

How Do You Read a Seed Analysis Tag?

A conservation tag carries a fixed set of lines, and each one has a job [1]:

• Purity, the percent of the lot that is the stated species: a purity of 90 percent means the other 10 percent is inert matter, weed seed, or other crop [1].
• Germination, the percent of seed that sprouted within a set period under specific lab conditions [1].
• Hard or dormant seed, the portion that did not sprout in the lab but is alive and respiring, with hard seed carrying a coat water cannot cross [1].
• Total viability, germination plus hard and dormant seed: 80 percent germination and 10 percent dormant seed is 90 percent total viability [1].
• Date of the assay, the month and year the lab ran the germination check [1].

Germination on the tag is a lab figure produced under favorable conditions, not a forecast for a seedbed, and it ages.

For NRCS programs, a germination figure on grasses and forbs, the broadleaf flowering plants that sit alongside grass in a native mix, can be no older than 9 months in South Dakota and 12 months in North Dakota and Minnesota, counting from the month after the assay [1]. A tetrazolium check reads viability in a day or two, and it cannot legally stand in for the germination figure on the tag [1].

How to Convert a PLS Rate Into Bulk Pounds

Conservation seeding rates are written in PLS pounds per acre, built on a target number of live seeds per square foot [3]. Most of those rates aim for somewhere near 20 to 60 live seeds per square foot, though very large or very small seed shifts the band [3].

The drill does not measure live seed. It measures weight, so the rate has to be converted before you order.

Divide the recommended PLS rate by the PLS percentage of the lot in hand, then multiply by 100 [2]. A plan calling for 10 PLS pounds per acre, filled with a lot that works out to 63.75 percent PLS, needs 15.69 bulk pounds per acre [2].

Penn State Extension runs the same math from the other end: a lot at 92 percent purity and 80 percent germination is 74 percent PLS, so 1.4 pounds of it covers each pound the recommendation asks for [4].

Multiply that bulk rate by your acres, and you have the order.

Why Do the Plan and the Food Plot Bag Disagree?

Most native plant seed is sold, and should be bought, on a PLS basis [1]. That covers the native grasses and wildflowers that fill most conservation plans.

Food plot blends often work the other way. Brassica, clover, and cereal grain mixes usually carry a bulk rate, because purity and germination on those crops tend to run high.

So a conservation plan and a food plot bag can print similar numbers that mean different things. Convert both to live seed before you compare rates, and before you compare price per pound.

Timing splits the same way. Brassica goes in first so the plants bulk up ahead of frost, cereal grains follow behind it, and clover can go in late summer or early spring depending on the region.

The Noxious Weed Line Is Worth Reading Twice

Each state names the weed species that are restricted or prohibited, and sets the maximum amount of restricted noxious weed seed a lot may carry [1]. Restricted species must be listed by name on the tag, with total seeds per pound [1].

Seed carrying prohibited noxious weed seed cannot be sold or planted in a state where it is listed as prohibited [1]. Other crop seed has to be named on the tag once it passes 5 percent of the content [1].

On habitat ground that line earns a second look: a weed you drill in is a weed you manage for the rest of the contract.

What Does the Cost-Share File Need?

CRP pays annual rent and covers up to 50 percent of the cost of establishing approved conservation practices, on contracts that typically run 10 to 15 years [5]. That reimbursement is paid against what you document.

For NRCS programs, collecting and submitting the seed tags for the species actually seeded in each field is the participant’s responsibility [1]. Keep the tag from every bag, photograph it before it goes in the trash, and file it alongside the seed invoice.

Pull the tag before you order rather than after. Run purity times germination for each species in the mix, convert the plan’s PLS rate into bulk pounds, and buy on live seed rather than on bag weight. If you are putting in a deer plot this fall, the Big Game Food Plot and Forage Mix from Nature’s Seed ships with its analysis tag, so you can work the numbers off your own lot before the drill goes in the ground.

Sources

[1] USDA Natural Resources Conservation Service. A Guide to Understanding Seed Tags. https://www.nrcs.usda.gov/plantmaterials/ndpmctn12317.pdf

[2] USDA Natural Resources Conservation Service. Understanding Pure Live Seed (PLS), Pacific Islands Area Plant Materials Technical Note 03. https://www.nrcs.usda.gov/plantmaterials/hipmctn13770.pdf

[3] USDA Natural Resources Conservation Service. Understanding Seeding Rates, Recommended Planting Rates, and Pure Live Seed (PLS), Louisiana Plant Materials Technical Note No. 11. https://www.nrcs.usda.gov/plantmaterials/lapmctn9045.pdf

[4] Penn State Extension. Calculating the Price of Pure Live Seed. https://extension.psu.edu/calculating-the-price-of-pure-live-seed

[5] USDA Farm Service Agency. Conservation Reserve Program (CRP). https://www.fsa.usda.gov/resources/conservation/conservation-reserve-program