Weighing the options of alfalfa seed treatments
The value of alfalfa seed treatments can be determined by several factors.
First, we need to define our population goal, which is to maximize alfalfa production per square foot. Following the seedling year, universities recommend an alfalfa stand of 18 to 20 alfalfa plants per square foot for pure alfalfa stands.
Next, we need to determine how many pounds of alfalfa seed per acre needed to reach that goal. Let’s do the math. If your alfalfa seed bag has 200,000 seeds per pound spread over an acre of land (43,560 square feet), you will need 5 pounds of seed per acre.
Traditionally, common seeding rates range from 15 to 25 pounds per acre. Your seed tag will provide more information to accurately predict the correct seeding rate based on your goal of 18 to 20 plants per square foot.
This planting rate, however, assumes 100 percent germination and survival rate, which isn’t realistic. Under normal conditions, only about 60 percent of seeds germinate, and up to 80 percent of the seedlings die within the first year due to natural selection. Germination, hard seed, seed-to-soil contact, moisture and seedling disease are just a few things that will affect your alfalfa seeding population.
Advancements in seed treatment technologies introduced seed coatings into the industry to provide more protection for the seed than standard treatments. The industry standard for seed treatments has been rhizobia bacteria for nitrogen fixation and a fungicide containing metalaxyl-M, a phenyl amide fungicide used to control soil-borne diseases caused by oomycetes fungi. These treatments can be dusty and appear to leach from the seed with the introduction of moisture during germination.
Enhanced seed coatings can reduce seed treatment dust and help nutrients adhere to the seed using calcium carbonate and polymers. Along with the standard rhizobia inoculant and metalaxyl-M fungicide, these coatings may also have additional components, such as insecticides, fungicides, micronutrients, and plant growth regulators.
These coatings will add weight to small seeds, which helps plantability, however, the large volume of inert material will decrease the amount of pure live seed purchased in a bag of alfalfa seed. These coatings can often account for 34 to 50 percent of the weight of a bag of alfalfa seed.
The common reaction to fewer live seeds per pound is to increase pounds of seed planted per acre, but this is not necessary as these enhanced coatings have proven to increase seedling survival. Breaking down the seed treatment components will help determine the true value of the treatment. Rhizobia bacteria can die over time if they don’t have enough soil coverage; coatings can help sustain live bacteria by increasing root nodulation and fixating nitrogen. Higher rates of fungicides can be added for additional seedling disease protection. The micronutrients and plant growth regulators can be beneficial to establish stands by providing essential nutrient requirements during germination, while the plant growth regulators can help break seed dormancy for quicker emergence.
Multiple studies have been done by universities and third parties on enhanced seed treatments to show an improved convergence of 60 to 80 percent of alfalfa seeds to healthy plants, compared to lightly coated seeds where 25 to 45 percent germinate into healthy plants.
Seed treatments can be a great value versus purchasing additional seed to achieve desired stand densities; you just need to weigh the options first. Contact your seed dealer or agronomist to help sort through the seed treatment options.
This article initially appeared in VitaPlus 2019 Forage Foundations. Murty is the forage products specialist for VitaPlus.