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Coated
Alfalfa Seed, is it worth it? Dr. Richard Leep, James DeYoung and Dr. Doo-Hong Min[1]
Most legumes such as alfalfa, clovers, and soybeans have a symbiotic (mutually beneficial) relationship with bacteria in the genus Rhizobium. The bacteria infect the roots of legume plants from which they obtain food, and the bacteria obtain nitrogen from soil air and “fix” it in a form usable by the plants. The nitrogen is accumulated in small appendages called “nodules” which form on legume roots (1). Rhizobia have always been required by legumes for inoculation (putting bacteria on the seed) and proper growth, the other ingredients in the mixture help the seedling in its very vulnerable state. According to some seed companies, the lime coating affects the soil pH surrounding the seed as it germinates and counteracts the acidity of other fertilizers added at the same time (5,6). This allows the rhizobia to survive and infect the root of the legume (2,6). It has also been suggested that the coating acts as a wick for water in times where moisture conditions are less than ideal. (4,6) According to other seed companies, coated seed is less likely to be eaten by birds and rodents because of its larger size and the lime or phosphorus coating (3). The coating can also protect rhizobia when coated seed is mixed with a granular fertilizer and broadcast applied in a one-step process. “Survival for the rhizobia decreases as the time of exposure to the fertilizer is increased” (3,17). Fungicides can also be added to the pelletization process. Fungicides can give the seedling an added boost by protecting against pythium and phytopthera root rot during the seedling stage. These diseases can kill young alfalfa seedlings when they are very vulnerable, especially when the environmental conditions favor the diseases (6,7). Various recipes have been suggested for mixing up your own coated or pelleted seeds. Most consist of the following ingredients, seed, rhizobia/peat inoculants, a gum or adhesive, and the finely crushed limestone coating. A concrete mixer or large container can be used to mix the ingredients (7,11). Care should be used when planting coated seed. Coated seed will weigh almost 1/3 (11) more than uncoated seed because of the added coating, and will flow through the planting equipment at a different rate than uncoated seed. It has been suggested that coated seed flows 30% faster than uncoated seed (opposite of what many people would expect). Other studies showed no change in rate of seeding (8,16). In any case, planters should be calibrated for the specific brand and type of seed used. The rhizobium in coated and pre-inoculated seed can die if it is stored too long or in warm temperatures for extended periods of time. The seed itself does not loose viability, but the rhizobium in the seed coating may no longer be viable. As with all rhizobia inoculants, the coated seed must be kept cool and dry. Checking the expiration date on all inoculants and coated seed when planting problems later. If in doubt of the age or viability of the inoculants, add fresh inoculant. A few ounces of prevention might be all that stand between a seeding success and a failure. (7,14) A study in Montana showed using lime-pelleted seed and a fertilizer combination of K, Mg, Mo and P could improve white clover establishment and growth on permanent-pasture soils in the acid soils of the northeast (with soil pH from 4.3-4.9). (13) By placing rhizobia next to the seed then surrounding that package with a systemic fungicide, seedling survival can be greatly increased if environmental conditions for pythium and phytopthera root rot are present. The fungicide helps the alfalfa seedling when it is most vulnerable to pythium and phytopthera root rot, while placing the rhizobia close to the germinating seed almost guarantees infection of the legume’s root and nodulation. With a higher survival rate for the seedlings, less seed is needed to establish a good stand. That is the rationale used to recommend planting coated seed, up to 1/3 less seed is used. Studies by Tesar in Michigan in 1976-77 showed no significant differences in stands or yield in the first two years of the alfalfa stand. Similar results were found in New York, Wisconsin and Minnesota. However, a recent study done in Minnesota showed results similar to the one done by Celpril. Strip trials were planted in thirteen locations in Minnesota to compare Rhizo-Kote XLâ plus Apronâ to pre-inoculated raw seed with Apronâ for establishment and yield. Stand counts showed Rhizo-Kote XLâ plus Apronâ with 7.5% more plants per square foot at establishment, and 11.1% more at the end of the season, when compared to the pre-inoculated seed. Yield was also increased in the Rhizo-Kote XLâ plus Apronâ with 19.8% more dry matter and a 4.3% gain in feed value when compared to the pre-inoculated seed. Using Rhizo-Koteâ in a study done by the University of Minnesota showed higher stand density early on, but by the fall of the seeding year, was not significantly different. In all the trials done, the results were too inconsistent to recommend using the coated seed (20). Research by Min (12) in 1986 – 1987 showed Celpril coated seed Rhizo-Koteâ and Rhizo-Kote plus Apronâ significantly increased the emergence, establishment, plant height, nodule number, and dry weight of alfalfa seedlings compared to uncoated alfalfa seed. However, dry matter yield of alfalfa following the seeding year was not affected by seed coating. Crude protein, acid detergent fiber, neutral detergent fiber, and in vitro dry matter digestibility were not affected by seed coating. Research in Kentucky also showed different seed flow rates between two seed coating companies. Celpril coated seed (Rhizo-Koteâ) flowed through drills at a faster rate than seed coated by Seedbiotics. Check the seed tag to be sure which one you have. The amount of increase in flow rate for Celpril coated seed appears to be 30% over uncoated seed at a setting that will deliver full seeding rates of alfalfa. The amount of increase at these same settings for Seedbiotics materials is about 22% (in a no-till drill mechanism). However, another study with a Brillion seeder calibrated with Seedbiotics coated alfalfa seed versus uncoated seed basically found no difference in seed flow due to the presence of coating. The bottom line is check drill calibration for proper seeding rate (16). In theory, at $15 less per bag compared to uncoated seed, is a quick way to save a little money when establishing a stand of alfalfa. The seed companies are selling less seed but the same numbers of plants becoming established. In summary, according to seed companies the benefits of planting coated alfalfa seed are better stands when compared to uncoated seed. A gain of $10.00 to $20.00 per acre increase in revenue per cutting could easily be achieved without incurring any additional production costs. However, in several independent university studies, the effects of seed coating on alfalfa establishment and yield were inconsistent over the years at different locations (19). Product disclaimer: Reference
to commercial products or trade names is made with the understanding
that no discrimination is intended and no endorsement by Michigan
State University is implied. References
In Southern Forages (2nd Edition). Potash and Phosphorus Institute (PPI) and the Foundation for Agronomic Research (FAR).
[1] Professor, Research Technician and Extension Specialist respectively. |
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