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Coated And Uncoated Clover Seed Have Different Planting Rates

published: October 4th 2010
by: Robert Burns
source: TAMU Ag Communications

Unless farmers want to chance reduced yields, they should probably stick with inoculating their clover seed themselves, according to a Texas AgriLife Research forage scientist.

"Or they should realize that they'll need to plant the coated seed at a higher rate per acre to get the same yields," said Dr. Gerald Evers, AgriLife Research forage management expert.

Even the ancient Romans knew there was something in some soils that made legume crops grow better, according to Evers.

"They didn't know what it was, but when they planted alfalfa on land that they had conquered, they knew to bring soil from where the crop grew well," he said.

What the Romans were doing, though they didn't understand the science, was importing a soil bacterium called rhizobium. The legume and the bacteria form a sort of "green" partnership, with the plant supplying carbohydrates the bacteria need to live, and in turn the bacteria remove nitrogen -- an essential plant nutrient --- from the air and make it available to the plant, Evers said.

Today, instead of importing soil, rhizobia are applied to the seed right before planting. A recently available alternative is to buy "coated" seed. The coated seed is pre-inoculated, then coated with a water-soluble clay, lime or talcum to protect the rhizobia from heat and sunlight, Evers said.

Agronomists have prescribed for decades that farmers inoculate their clover seed and other legumes at planting in the fall to ensure the best bacterial strains are present, Evers said. Though the bacteria can occur naturally, many soils are deficient or don't contain the most efficient strains, and there is not a simple test to determine how much or what type is present.

Today, many farmers still don't understand the science any more than the ancient Romans did and many either don't do a good job of inoculating seed or don't do it all, he said.

"Hence, the rationale for coated seed," Evers said. "There's also the labor-saving aspect of having the seed pre-inoculated."

Seed companies posit that seed germination and seedling vigor are greater for coated seed and therefore yields would be similar, according to Evers.

"To my knowledge, no one else in the U.S. has tested this theory," he said.

However, preliminary results of Ever's study indicated that when planted at the same seeding rate, coated clover seed produced lower yields than seed that was inoculated at the time of planting.

At issue is the number of seeds per pound of product, he said.

"The kicker is that the coating comprises 25 to 45 percent of the weight of a bag of seed," he said.