Simple Yet Complex

July 25, 2014 09:17 PM
Simple Yet Complex

Why talc and graphite are necessary in planters

In the midst of the frantic pressures of planting season, two niggling questions tug at farmers’ minds every time they fill their planter. How much graphite or talc should be added per planter-fill, and why the heck is graphite or talc even necessary?

"Graphite is a dry lubricant used to decrease wear in mechanical seeding mechanisms," explains Kelby Krueger, product specialist at John Deere. "Finger pickup units are a good example. Graphite reduces friction in those units and increases component life."

Talc, which is recommended as a seed coating in "air" planters, also acts as a dry lubricant, but its primary role is a drying agent. The fans in air-based seed metering systems move tremendous volumes of air. Even low levels of humidity in the air are magnified by high air flow and cause problems with pesticide coatings commonly applied to seeds.

Better seed flow. These insecticide and fungicide coatings are hygroscopic, meaning they readily absorb moisture from the high volumes of air moving through air planters. When they absorb moisture, their surfaces become sticky, leading to problems with seeds clumping and bridging in seed hoppers and clinging to seed disks in seed meters.

"The coatings on seeds get rougher and stickier when they absorb moisture," Krueger says. "Talc fills the pores, smooths and dries the surfaces of the seeds and improves flowability."

Weather systems that bring in low humidity might reduce problems with seed treatments, but it also increases another seed metering problem that is related to static electricity. 

As the plastic metering disks turn in seed meters, static electricity can develop on the surfaces of seeds as they jostle in the bottom of the hoppers or as they rattle through plastic seed delivery tubes. The static electrical charges cause seeds to clump and bridge.

"Static electricity can be a big problem with some seeds," says Daryl Cress, service manager at Great Plains Manufacturing. "It varies between different types of seeds, seed coatings and conditions. Milo and canola seem to have the worst problems."

Fortunately, talc and graphite have anti-static characteristics. Talc is an insulator, minimizing the buildup and transfer of static electricity. Graphite is a conductor, easily transferring to "ground" within a planter’s components any static electricity that develops. An 80/20 mix of talc and graphite provides air planters with optimum seed drying capabilities as well as sufficient static electricity control.

How much? The key to applying proper amounts of graphite, talc or a talc and graphite mix to seed in hoppers depends on the product. 

Kenny Dill, tech support at Precision Planting, says the goal with graphite is to provide adequate lubricity to mechanical planter components without dirtying the seed tube sensor to the point it reduces seed monitoring precision. In finger pickup seed meters, excess graphite can also increase the chance of skips.

"Adding too much graphite can make the seeds so slippery the fingers have trouble holding them," Dill explains. 

Extra talc has no detrimental effects, except on the farmer’s wallet.

"Excess talc generally gets blown into the atmosphere," Krueger says. "The issue is about wasting money. The key is to premix talc into the seed so that every seed is evenly coated. Just adding talc to the top of seed hoppers generally doesn’t give a good uniform coating, and you end up with wasted talc accumulating in the bottoms of the hoppers or getting blown into the atmosphere."

Graphite and talc application rates vary based on planter type, weather conditions and seed coating type. Manufacturers of finger pickup seed meters recommend 1 to 2 tablespoons of graphite per bushel of corn. Air planter manufacturers suggest starting the season with ½ cup of talc per bushel, then increasing or decreasing rates as required by humidity and seed coatings to maintain seed flow.

Bees, Talc and Bans

Talc is widely used as a coating to improve seed flow in planters, but controversy over damage to bee colonies has led to restrictions on the use of talc in Canada.

"As it stands now, Canadians aren’t allowed to use talc on treated seeds," says Kelby Krueger, product specialist at John Deere. "They can use talc on untreated seed because untreated seed isn’t the issue."
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The restrictions stem from research that indicates damage to bee colonies in ag areas might be related to neonicotinoid insecticides that are used as seed treatments. The insecticides readily attach to talc applied to seed. When fans on planters blow tainted talc off seed, the residue settles on plant leaves and flowers. As bees crawl on the plants, the insecticide-laden talc adheres to their bodies and is carried back to the hive.

Based on research by Iowa State University, even a miniscule amount of insecticide can harm bees. A single kernel of corn with the recommended rate of neonicotinoid insecticide has enough active ingredients to kill more than 80,000 honeybees.

Talc by itself is not a danger to insects. "Talc is nearly chemically inert and not the problem," Krueger says. "The issue is the insecticide that is absorbed by the talc and then spread into the atmosphere."

U.S. regulatory agencies are researching the issue and might follow the lead of Canada and Europe that ban the use of talc on treated seed. U.S. ag companies are proactively seeking alternatives to talc if that happens.

"We’re planning on talc and graphite eventually being banned in the U.S.," says Daryl Cress, service manager at Great Plains Manufacturing. "The current alternative in Canada is Fluency Agent sold by Bayer."

Bayer’s Fluency Agent is a wax-based lubricant that minimizes dispersal into the air. It has lubricating and static electricity-reducing properties similar to talc and adequate seed flowability.

Seed companies are looking for alternatives to neonicotinoid insecticides to sidestep the issue. 
"Neonic-free" seed treatments are available in Canada and might be released in the U.S. in the future.      


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