Closing wheels should be more than an afterthought
The simplicity of closing wheel systems on planters belies their importance. Studies show even perfectly metered seed accurately placed in a seed furrow can face germination and emergence issues if closing wheels pack soil over or around seed.
“The goal of closing wheels is to close the furrow without air pockets touching the seed,” says Cory Muhlbauer, research and development agronomist, Precision Planting. “You want the seed in firm contact with the soil for good water imbibition, but you don’t want the soil packed around the seed.”
Traditional planter furrow closing systems use two rubber-tired wheels set at precise angles to press the sides of the seed furrow closed. Soil directly over the seed is left soft for easy emergence.
Tined closing wheels and drag chains can help leave soil loose over the seed furrow for seedlings to emerge.
Excess down pressure on closing wheels can press the seed and adjoining soil down so much it stymies root growth. Improperly adjusted gauge wheels or worn frame bushings can position gauge wheels so they run directly over the seed furrow, forcing seed to work to emerge through packed soil.
In most cases, conventional closing wheels do a good job firming soil around seeds as long as they’re properly aligned and down pressure is adjusted to match soil conditions. Unique soil conditions might benefit from optional closing wheel designs.
“There are situations in no-till or when planting at more than 7 mph when the extra mass of cast iron closing wheels helps close seed furrows without really cranking up the down pressure on the closing wheel frame spring,” Muhlbauer says.
Tined closing wheels of various designs have become popular, especially when wet soils challenge the ability of conventional options. Planter manufacturers say if conventional closing wheels can’t close seed furrows, it’s probably too wet to be planting. But they acknowledge tined wheels have benefits under certain conditions if used appropriately.
“[Tined closing wheels] are useful in conditions where conventional closing wheels might not completely close the furrow,” says Drew Gerber, Horsch North America. “If most of a field is ready to plant but there are wet spots and you can’t wait until the entire field is dry, it can help to have some sort of tined closing wheel that provides light tillage of the furrow wall to help close the furrow in the wet spots.”
Straight-tined closing wheels must be set with care to avoid penetrating so deeply they disturb seed placement. Curved-tined and plastic closing wheels with short, stubby fingers are less prone to overpenetrate.
Be cautious when operating tined closing wheels on high-speed planters. Any tined closing wheel risks rooster-tailing and excessive soil movement if planting speeds exceed 7 mph.
Regardless of the type of closing wheel farmers use, the only way to adjust for optimum seed-to-soil contact is to get dirty knees.
“It’s not enough to dig up one or two seeds,” Muhlbauer says. “I like to dig up a 10' length of row and look at the soil conditions around each seed. And I’m careful about how I dig those seeds.”
“Going badger” when digging seeds ignores the subtle adjacent soil conditions. Muhlbauer prefers to sneak up on seeds as he excavates them.
“I dig slow and take into account how the soil looks and feels on top of, beside and underneath the seed,” he says. “Most closing wheel systems look good on the surface, but what really matters is how they manage the soil around and in contact with the seed. That’s what matters when it comes to getting consistent germination and emergence.”