Talc and graphite lubricate mechanical planter components and improve seed flow.
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.