Alfalfa seeding rates, stand counts reviewed

Ray Mueller
Now Media Group


What's the right seeding rate for alfalfa? What's the difference between coated and noncoated alfalfa seed? And how are alfalfa yields faring in Wisconsin?

Those questions were explored at the 2016 educational program and annual meeting of the Outagamie County Forage Council by the county's Extension Service crops, soils and horticulture agent Kevin Jarek.

Citing alfalfa establishment costs of approximately $330 to $360 per acre, Jarek suggested alfalfa growers should benefit by being aware of the latest research findings and the changes being introduced by seed suppliers.

Numerical fundamentals

With 1 pound of noncoated alfalfa seed containing about 199,000 seeds, Jarek pointed out that a theoretical seeding rate of 1 pound per acre would place 5 seeds per square foot. An actual seeding rate of 15 pounds per acre would result in an average of 75 seeds per square foot.

For a number of years, the Extension Service was recommending seeding rates of 12 pounds per acre, but more research has shown that 10 pounds of pure live seed per acre is sufficient for establishing alfalfa in Wisconsin and in the Midwest, Jarek reported.

Regardless of the planting rate, there's a high mortality rate on alfalfa plants that germinated due to combinations of field practices, natural factors and plant competition that tends to reduce the plant count to between 15 and 25 per square foot by the spring after the seeding year, he said.

At a 10-pound per acre seeding rate, that's a mortality rate of 45 percent, while a 20-pound per acre seeding rate would typically result in a mortality rate of at least 70 percent — both resulting in about the same number of plants per square foot, Jarek said. From a high seeding rate, the first two rounds of mortality would leave the number of live plants by the second full year of a stand at only 12 percent of the number of seeds that were planted.

Coated seed calculations

What constitutes 'a pound' of seed has also changed, Jarek indicated. He noted that about 70 percent of the seed provided by suppliers is coated with such items and substances as limestone, gypsum, polymers and low amounts of rhizobia and fungicides in order to protect the seeds through germination and the early stages of life.

Growers need to be aware of how this affects their intended seeding rate because it alters the number of pure seeds in a pound of purchased seed, Jarek stressed. He noted that the coating accounts for 34 percent of the weight of seed provided by one leading supplier and for 9 percent in the seed from another company (information that's available on the seed tag).

Another clue to the effects of coating is in the pricing difference per bag for the various products. He finds that the seed companies are properly pricing their seed based on whether it is coated or not.

Jarek also reminded alfalfa growers to check the seed label for the indicated percentages of purity, germination and hard seed because of what the seeding rate of viable seed would be. He noted that hard seed does not germinate immediately but could do so later in the seeding year or even the following year.

With Extension Service and forage association funding, research plots for comparing coated and noncoated seed were carried out in Outagamie and Calumet counties during 2015, Jarek reported. Not surprisingly, some of the results were 'things beyond our control,' but there was a surprise in the amount of hard seed that eventually germinated in the Calumet County plot to boost the plant population.

Persistence project

Jarek provided a summary of the Wisconsin alfalfa yield and persistence project that began in 2007 and included 24 fields in eight counties around the state during 2015. Outagamie County accounted for seven of those fields, while Fond du Lac and Marathon counties had four each.

The overall results for 2015 indicated an average year for both yields and quality, Jarek pointed out. With four cuttings taken from most of the fields, the per acre dry matter yields ranged from 2.7 to 5.95 tons with an average of 4.4 tons.

Noticing that 70 percent of the fields enrolled in the project are still yielding less than than 5 dry matter tons per acre, Jarek suggested that 'there's plenty room for improvement' on alfalfa production.

While there continues to be an invitation to more alfalfa growers to have their fields added to the yield and persistence project data set, Jarek announced that he will not be undertaking any new forage research projects for the 2016 growing season because of the uncertainties associated with the impending restructuring of the Extension Service at county levels due to continuing budget cuts by the state legislature.