Unless farmers want to chance reduced yields, they should probably inoculate clover seed themselves, according to Gerald Evers, Texas AgriLife Research forage management expert.
"Or they should realize that they'll need to plant the coated seed at a higher rate per acre to get the same yields," he says.
A recently available alternative to applying rhizobia to seed right before planting is buying coated seed. Coated seed is pre-inoculated, then coated with a water-soluble clay, lime or talcum to protect the rhizobia from heat and sunlight, Evers says.
Inoculated clover and other legume seed at fall planting ensures the best bacterial strains are present, Evers says. Though the bacteria can occur naturally, many soils are deficient or don't contain the most efficient strains. There is not a simple test to determine how much or what type is present, he adds.
Many farmers either don't do a good job of inoculating seed or don't do it all, he says. "Hence, the rationale for coated seed. There's also the labor-saving aspect of having the seed pre-inoculated."
Seed companies say coated seed offers greater seed germination and seedling vigor and, therefore, yields would be similar between it and seed inoculated at planting, according to Evers. "To my knowledge, no one else in the U.S. has tested this theory."
But Evers has compared coated clover seed with inoculated-at-planting seed. Preliminary results of his study indicate that, when planted at the same seeding rate, coated clover seed produced lower yields.
At issue is the number of seeds per pound of product, he says.
"The kicker is that the coating comprises 25-45% of the weight of a bag of seed.” Although farmers pay about the same per pound for uncoated as coated seed, they may get only three-quarters to half the number of seeds per bag of coated seed compared to a bag of uncoated seed. But seed companies recommend the same planting rates in terms of pounds per acre, he says.
In the first year of his study (2008-2009), Evers did not find any yield differences. But in the second year, per-acre yields for uncoated seed were significantly higher than coated in the first harvest for hay. There was no significant difference in yields for the second cutting.
The first year of the study, when yields didn't differ between the two types of seed, it was abnormally dry. The second year, when there was a significant advantage to using uncoated seed, there was adequate moisture. He has extended the study another year and will plant this fall, because the first year wasn't representative of average conditions.
"That is, if Mother Nature gives us enough moisture," he says.
To ensure similar yields when using coated seed, farmers should calculate how many pounds of seed are actually in a 50-lb bag. The coating is listed on the seed bag label as the percentage "inert material." If inert material is listed as 25%, a 50-lb bag will contain only about 75% seed or 37.5 pounds of seed.
"And they should adjust their planting rate accordingly," he says.
Farmers can save money by inoculating their own seed – if they do it correctly, Evers says. Too often, farmers fill up planter seed boxes, sprinkle on inoculant and stir it around. But the best method is to use a portable cement mixer.
"Put a 50-lb bag of seed in the mixer, then turn the mixer on," he says. "With the mixer turning, pour in one to two pints of water. Let the mixer run until all the seed are moist, then add the bag of inoculant."
Run the mixer 30 seconds to a minute to thoroughly coat the seed.
"Then put the inoculated seed back in the bag and let it dry before you put it in the planter. If you don't, it will not flow smoothly through."