Forage Seed Selection and Quality
Pasture establishment or renovation will be only as good as the seeds that are planted. Growers are encouraged to consider seed selection carefully because understanding the components of seed quality and selecting high-quality seeds can save time and money during forage production. Beyond this, the quality of the forage crop itself will have a direct impact on animal health and performance: High-quality forage produces healthier animals and better meat and milk for market. This publication describes forage seed quality and provides information to help growers make informed decisions about which seeds will best fit their farming situation.
Forage seed quality depends on three key components: germination, genetic purity, and crop purity. The importance of each is described below.
Germination. Germination is the measure of how well a seed produces a normal, healthy seedling when planted under ideal conditions. The standard germination test, evaluated under the temperature considered ideal for each species, provides an estimation of seedling emergence if soil conditions at planting and during early seedling growth are near optimum. The results of the standard germination test are printed on the seed tag (Figure 1).
Each species has a specific range of temperatures at which germination occurs. If temperature at planting falls outside this range, germination may be slowed or prevented, and during extreme conditions the seedlings may die. Excessively high or low temperatures also can induce secondary seed dormancy, causing a delay in germination and establishment. It is therefore important for growers to be aware of the germination requirements of the species that is planted and to sow fields when conditions are favorable. Suggested planting dates usually reflect the requirements for specific species and are listed in Production and Utilization of Pastures and Forages in North Carolina (Technical Bulletin Number 305, N.C. Agricultural Research Service, North Carolina State University).
It is essential that forage seed have adequate moisture immediately following planting to promote rapid germination and for a period of about three weeks after emergence to promote seedling growth.
Genetic Purity. Varieties are adapted for specific uses and production areas. The genetic constitution of a variety will influence disease and insect resistance, plant response to climatic extremes, forage quality, and many agronomic characteristics. Growers should purchase seed of a known variety that has been tested for their area.
In North Carolina, forage seed may be sold variety not stated. However, growers should realize that purchasing seed of an unknown variety often leads to low yields, reduced stand life, and increased cost.
Genetic purity, or trueness to variety, is established and maintained by special purification and seed increase programs, by field and seed inspections, and by pedigree records. The best assurance of obtaining genetically pure seed is to buy certified seed, clearly identified by the "blue tag" (Figure 1). The blue certified seed tag is issued only to seed lots that meet specific genetic, physical, and physiological standards.
Crop Purity. Seed lots with even small amounts of weed seed or other crop seed can cause serious economic losses and diminish forage quality. Weeds and other crop plants compete with the desired species for nutrients, space, and soil moisture and are often difficult or expensive to control. Some weeds, such as serrated tussock, Canada thistle, or horsenettle, can harm animals or threaten pasture value. Other weeds that are frequently found in forage seed include dock, sedge, wild garlic, wild onion, mustards, panicums, and other forage seeds such as ryegrass.
Figure 1. The seed tag contains essential information about seed quality.
SEED ANALYSIS TAG
The North Carolina Seed Law requires containers of seed offered for sale to be labeled for content. The seed analysis tag or label contains information based on germination and purity analysis of a representative sample taken from the seed lot.
The N.C. Seed Law prohibits the sale of forage seed that
Fall below 70 percent germination.
Contain more than 1 percent weed seed.
Contain excessive amounts of restricted noxious weed seed.
Contain any prohibited noxious weed seed.
Here is a description of the information offered on the seed tag:
Kind and Variety. The "kind" of crop refers to the species. North Carolina does not require the forage variety name to be listed on the tag. However, if the variety is not given, the seed tag should bear the statement, variety not stated. When two or more varieties or kinds are named, the word "mixture" or "mixed" must appear on the label. Bermudagrass, often called common bermuda, is no exception to these rules. The sale of "common" bermudagrass requires either the variety name or the notation variety not stated.
Germination. This notation tells the percentage of pure seed that germinates. The percentage is based on the number of seeds that produced normal seedlings following a specified test period (a normal seedling being one that has the essential structures necessary for plant survival). If more than one kind and variety are named, the germination percentage must be shown for each.
Some forage species are dormant when harvested, and the dormancy period may last for a few weeks to several months. When seeds are dormant, they are still viable but will not germinate when placed in the proper germination environment. Special pre-conditioning treatments must be used to break or overcome this dormancy. Switchgrass is a good example. Its seeds must have a pre-chill treatment for 2 weeks at 40°F to condition the seed for germination. Also, the seeds must be fully imbibed during the pre-chill treatment. When switchgrass is labeled 90 percent germination on the seed tag, it takes into account two weeks’ pre-chill treatment during the test to break dormancy, followed by two weeks in alternating 60/85°F to measure germination potential.
It is possible to buy seeds that have high germination potential, but if dormancy has not been broken, they will not germinate well when planted. Dormancy of most species can be broken by storing the seeds at room temperature for several months before planting.
Origin. This label entry identifies the state or country in which the seed were grown. If the origin is unknown, the statement origin unknown must appear on the label.
Lot Number. Lot number allows the seed producer and buyer to identify the specific unit from which the seed were taken. The term "lot" means a definite quantity of seed that is uniform throughout for the factors that appear on the label. This information is useful in cases of performance problems.
Net Weight. This is the weight of the seeds only – minus the weight of the container.
Pure Seed. This percentage tells the total weight of seeds of the kind and variety stated on the tag. If more than one kind or variety is named, the pure seed percentage of each component must be given.
Inert Matter. Extraneous material, such as dirt, stems, leaves, and seed parts in the seed lot, is described in this percentage. Inert matter reduces the value of seed. It is best to choose seed with less than 2 percent inert matter.
Other Crop Seed. The percentage of the total weight from seed from a crop other than the kind and variety listed is indicated here. High-quality seed should contain no seed from other crops. The presence of other crop seeds in forage grasses can be particularly troublesome. Annual ryegrass in fescue is considered "other crop seed," not weed seed. The presence of 0.05 percent ryegrass in a forage translates into as many as 120 ryegrass seeds per pound of fescue. At a planting rate of 15 pounds per acre, this could mean as many as 1,800 ryegrass plants per acre of pasture.
Weed Seed. Weed seed contamination is expressed as a percentage of the total weight. This classification includes seeds, bulblets, or tubers of plants recognized as common weeds by official regulations or by general agreement. Weed seeds are typically very small, so a small percentage of contaminants can translate into many weed plants. High-quality seed should contain less than 0.2 percent weed seed.
Seedsman or Vendor. The name and address of the person or company labeling the seed are given on the seed label. They are responsible for the accuracy of the label.
Hard Seed. Hard seed are viable, but have a seed coat that is impermeable to water. Where hard seeds are present, total germination percentages are customarily determined by combining germination and hard seed percentages.
Test Date. The law requires that the germination test must have been made within nine months of the date the seed are sold or offered for sale (not counting the month of the test). The law also requires the individual owning the seed to keep the germination test date current, so carryover seed should be retested and re-labeled before the original test date expires.
Treated Seed. Seeds that are treated with chemicals must be labeled to show the chemical used, and the words "Caution," "Poison," or "Poison Treated" must be written on the label, depending on the harmfulness of the seed treatment to humans. In addition, the statement, "Do not use for food, feed, or oil purposes," also must be printed on labels of treated seed, and the seed must be dyed a bright color.
Endophyte. The N.C. Seed Law does not require labeling for endophyte in tall fescue. However, if the seed are labeled, the N.C. Department of Agriculture and Consumer Services (NCDA&CS) does check to ensure levels of endophyte are correctly stated. If a discrepancy is found, a "stop sale" will be placed on the seed lot.
Noxious Seed. The name and number of all noxious weed seed must be listed on the tag.
NORTH CAROLINA’S SEED BOARD
The North Carolina General Assembly recently passed a law to help resolve seed performance complaints outside court. A grower who purchases seed that fail to perform as labeled (for example, poor germination, weed seed present, or mislabeled variety) may file a complaint with the Commissioner of Agriculture to have his or her seed complaint investigated by the N.C. Seed Board. Details on filing a complaint can be found in Handling Seed Complaints, AG-596, available from the county Cooperative Extension Centers and NCDA&CS.
High-quality forage seed can be stored successfully for more than one season if it is kept in a cool, dry environment. In general, the shelf life of grass seed stored at room temperature (77°F) is roughly two years. Orchardgrass and tall fescue, however, are exceptions and can be stored for only about one year (Figure 2). Legume seed storage potential is fairly good; most can maintain germination for two years, with the exception of crimson clover, which can be stored only one year.
Tips on Storing. Avoid storing seeds in metal storage buildings or attics. Temperatures there can be extremely high during the summer, and it does not take long under these conditions for germination potential to be destroyed. Basements are well suited for seed storage as long as moisture can be controlled.
Forage seeds may be stored in freezers; however, freezing temperatures may kill Endophyte and Rhizobia.
|Seeds are a tempting food source for rodents and many insects. To protect seeds from rodents, store them in metal trash cans with the lid securely fixed. To control insects, tape no-pest strips on the inside of the lids. Do not insert the strip into the seed bag. Replace the strips every two to three months.||
Figure 2. Seed germination of several forage species before and after storage.
Vitality Test. After storage, it is essential to test seed for germination at least one month before anticipated use. This will allow time to locate fresh seed if germination has declined to low levels during storage. NCDA&CS’s Seed Testing Laboratory will perform germination tests for North Carolina growers at no cost. Send a one-half pound sample to NCDA&CS Seed Testing Lab, P. O. Box 27647, Raleigh, NC 27603-7647 and indicate that the sample is for germination analysis only.
The seed lab also can test seed lot viability using the tetrazolium chloride (TZ) test. TZ tests can be performed in 24 hours, giving growers an accurate and rapid evaluation of seed lot quality. There is a small charge for TZ tests.
Seeding rates should be based on the amount of pure live seed (PLS) in the seed lot. This is particularly true for chaffy native species with fluffy seed coats or large awns or for seed that are difficult to clean. In the latter case, the seed contain large amounts of inert matter, which makes calculating seeding rates difficult. Suggesting seeding rates based on bulk seed weights can result in low plant populations. Common species like fescue, ryegrass, orchardgrass, and legumes generally have 95 percent or greater purity with germinations above 90 percent. Therefore, it is customary to suggest planting rates based on bulk seed (pounds of seed per acre).
||PLS is calculated by multiplying seed lot germination by purity.|
|For example, if germination is 90 percent and pure seed 90 percent, PLS is 81 percent [(90 x 90) ¸ 100].|
The actual seeding rate based on PLS can be calculated by dividing the recommended rate by the PLS. If the recommended seeding rate is 15 pounds per acre, the actual seeding rate would be: 15 pounds per acre ¸ 0.81 = 18.5 pounds per acre.
AT-HOME GERMINATION TEST
It is always best to have the NCDA&CS Seed Lab or other seed-testing facility perform an accurate evaluation of germination because a trained seed analyst can best judge germination potential. Many forage species also require special germination-test environments not readily available to growers. Some freshly harvested species require special pre-chill treatments before they will germinate. It is best to have a reliable evaluation of fresh seed performed by a qualified laboratory.
Growers who want to test carryover seed, not fresh seed, at home may use the following procedure:
1. Wet three paper towels with tap water. Hold the towels by one corner for several seconds to allow excess water to drain.
2. Place two towels together (back to back) and smooth them on a flat surface. Put the third towel to one side.
||3. Place 100 seeds on top of the two flat, moist towels, and scatter the seeds evenly so that none is touching.|
||4. Cover the seeds and towels with the third towel.|
||5. Gently roll the towels into a tube. The tube should not be too tight, for this will restrict seedling growth.|
||6. Place the tube in a large, clear plastic bag. Punch a few small holes in the bag to allow some air movement. Put the bag near a window. Arrange the bag so that the towel tubes are nearly vertical. (This allows the roots to grow downward and makes counting much easier). Do not place in direct sunlight. Too much sunlight might raise the temperature too high inside the plastic bag. Keep the towels moist, not saturated, throughout the germination period.|
||7. Take germination counts 7 to 14 days after planting. To be counted as germinated, the seedling should have a strong root and shoot.|
Clover and alfalfa may contain dormant hard seeds, which are
typically counted as germinated in the test. To determine if seeds are dormant
or dead after the allotted time in the germination towels, press the ungerminated
seeds firmly into the towel with your finger. If the seed is hard, not mushy,
it should be counted as germinated.
Germination, as determined by this at-home test, is the number of seeds out of the 100 tested that sprouted and had healthy seedlings (including the number of hard seeds). Compare this percentage to the germination percentage on the original seed tag, and plan the seeding rate of the carryover seeds accordingly.
The yield and quality of a pasture’s forage, as well as animal performance on the forage, can be influenced by the species and variety selected and by the quality of the seed purchased. Growers should read the seed tag carefully and purchase only those seed lots of adapted varieties that meet the standards known to promote a healthy, weed-free, high-quality pasture.
J. F. Spears, Extension Seed Specialist, Crop Science Department, North Carolina State University,
J. T. Green, Professor, Crop Science Department, North Carolina State University
Published by NORTH CAROLINA COOPERATIVE EXTENSION SERVICE
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
9/01– JL AGW-004 E01-38927