Craig Sheaffer, Extension forage agronomist
Establishing a productive stand of alfalfa or other forage begins with quality seed. The seed label contains information that allows farmers to evaluate the quality and value of the seed they purchase.
Attached is a fictional/example alfalfa seed tag showing information required by the Minnesota seed laws. While all the information is important in describing the seed in the bag, there are several key items to pay attention to.
R. Newell. It’s on the tag and in the bag. 2018. Hay and Forage Grower. https://hayandforage.com/article-1331-It%E2%80%99s-on-the-tag-and-in-the-bag.html
C. Sheaffer. 2023. Alfalfa establishment: management strategies. https://extension.umn.edu/planting-forages/alfalfa-establishment-management-strategies#:~:text=Recommended%20rates,on%20yield%20(Table%203).
Determining the Optimum Alfalfa Seeding Rate by Mike Rankin https://fyi.extension.wisc.edu/forage/files/2014/01/AlfSeedingRate-FOF.pdf
D. Undersander, Pure live seed. Univ. Wisconsin.
https://fyi.extension.wisc.edu/forage/pure-live-seed/
D. Undersander et al., 2014. Alfalfa Management Guide. American Society of Agronomy, Inc. Crop Science Society of America, Inc. Soil Science Society of America, Inc.https://www.agronomy.org/files/publications/alfalfa-management-guide.pdf
The seed label
Federal and Minnesota seed laws require labeling of all seed sold to farmers. This applies to a single crop or a mixture and applies whether the seed is sold on-farm or at a retail business. Information on the seed label helps growers evaluate the quality and value of the seed. They also provide for fair marketplace competition among seed suppliers. To ensure truth in labeling, the Minnesota Department of Agriculture inspects seed.Attached is a fictional/example alfalfa seed tag showing information required by the Minnesota seed laws. While all the information is important in describing the seed in the bag, there are several key items to pay attention to.
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| A fictional alfalfa seed label. |
Kind
The kind identifies all desired species present in the bag. This applies to both single crops and mixtures. On the fictional tag, alfalfa is identified as the single crop.
Variety
In this example, the variety name is Dozer II. If the seed is a Brand and labeled as “variety not stated” (VNS), then the variety and its genetics in the bag are unknown. Brands are often cheaper than named varieties, but can contain mixtures of several unknown varieties.Pure seed
Pure seed is the amount of single crop or mixture reported on a percent weight basis. For example, a purity of 65.8% - like the example label - indicates that 34.2% of the bag contents is inert matter (chaff), coating, weed seed, or other crop seed.Germination
Germination reports the percentage of total crop seed that germinates within a designated time period for the crop species.Hard seed
Hard seed is the percentage of viable seed that germinates after the designated times. For most alfalfa seed, hard seed content will be 10% or less. In this example, it's 5%.Germination & hard seed
Germination & hard seed is a sum of both of these percentages. On the example tag, the sum of these two categories is 95%.Date of test
The test date reports the month and year the seed test was conducted. Older seed might have reduced germination depending on its storage conditions. In Minnesota, seed must be tested every 12 months and re-labeled with updated information.Seed inoculation
Alfalfa and other legume seed is coated with Rhizobium inoculum to ensure effective inoculation. However, Rhizobium cannot survive indefinitely on the seed, so it's important to note the expiration date for the seed inoculum. As a living bacteria, it has a finite lifespan on the seed. If seed is saved from season to season, reinoculation is necessary.Coating
Alfalfa seed is often coated with fungicides to protect seedlings from seedling disease, the inoculum Rhizobium, as well as colorants. Polymers are used to separate these components and protect the Rhizobium. Other coatings may include minerals such as mica and limestone and hydroscopic materials. Coatings must be described on labels.Weed seed
In Minnesota, seed sold cannot contain more than 1% weeds by weight. You will seldom see an alfalfa seed label with weed content over 0.10%.Determining pure live seed (PLS)
The amount of PLS within a bag is critical information because it is the PLS that has the potential to germinate and produce a stand of alfalfa. It will affect the amount and cost of seed used. Pure live seed is calculated by multiplying the pure seed percentage by germination percent. Using the fictional seed tag, calculate PLS below:Seed bag #1
Calculate pure live seed for seed bag #1
PLS = pure seed% x total germination/100
PLS = (65.8 x 95)/100 = 62.5%
Therefore
- in a 50 pound bag of seed there are 31.25 lbs of PLS (50 x 62.5%)
- to achieve a 15 lb PLS/acre seeding rate, 24 lb/acre of the seed would be needed (15 / 62.5%)
Seed bag #2
Seed bag #2 has only 80% germination rate. Use the formulas above to calculate PLS.
PLS = (65.8 x 80)/100 = 52.6%
Therefore
- in a 50 pound bag of seed there are 26.3 lbs of PLS (50 x 52.6%)
- to achieve a 15 lb PLS/acre seeding rate, 28.5 lb/acre of the seed would be needed (15 / 52.6%)
Table 1. Characteristics in two alfalfa seed bag examples
| Bag 1 | Bag 2 | |
|---|---|---|
| Total germination (%) | 95.0 | 80.0 |
| Pure seed (%) | 65.8 | 65.8 |
| Pure live seed (%) | 62.5 | 52.6 |
| Pounds PLS in 50 lb. bag | 31.2 | 26.2 |
| Pounds for 15 lb PLS/acre | 24 | 28.5 |
| Seed costs @ $7/lb | $168/acre | $200/acre |
Summary
- Federal and Minnesota seed laws require labeling of all seed sold to farmers.
- The seed label states the species and variety name as well quantity of pure live seed (PLS).
- Pure live seed in a bag defines the quantity of viable seed within a bag. With decreases in either total germination or pure seed, PLS content will decrease. In our example, Seed Bag 2 has about 5 lb less pure live seed than Seed Bag l. Therefore, it has less value.
- With a decrease in PLS, seeding rates should be adjusted. For example, to achieve a 15 lb/acre rate, if seed in Bag 2 is used, seeding rate should be increased by 4.5 lb/acre. This will result in additional seed costs for establishment.
Additional reading
D. Theide. Seed Labels in Minnesota. Minnesota Department of Agriculture. https://bugwoodcloud.org/mura/mipn/assets/File/UMISC-2018/Wednesday/PM/Thiede_Seed%20Labeling%20in%20Minnesota.pdfR. Newell. It’s on the tag and in the bag. 2018. Hay and Forage Grower. https://hayandforage.com/article-1331-It%E2%80%99s-on-the-tag-and-in-the-bag.html
C. Sheaffer. 2023. Alfalfa establishment: management strategies. https://extension.umn.edu/planting-forages/alfalfa-establishment-management-strategies#:~:text=Recommended%20rates,on%20yield%20(Table%203).
Determining the Optimum Alfalfa Seeding Rate by Mike Rankin https://fyi.extension.wisc.edu/forage/files/2014/01/AlfSeedingRate-FOF.pdf
D. Undersander, Pure live seed. Univ. Wisconsin.
https://fyi.extension.wisc.edu/forage/pure-live-seed/
D. Undersander et al., 2014. Alfalfa Management Guide. American Society of Agronomy, Inc. Crop Science Society of America, Inc. Soil Science Society of America, Inc.https://www.agronomy.org/files/publications/alfalfa-management-guide.pdf
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