Too much down pressure can hinder root development. In this no-till plot, down pressure was set at 400 psi on the left and 100 psi on the right.
Correct down pressure is critical to perfect stands
The genetic potential of a corn seed is essentially unlimited. Once you place the seed in the ground, whatever happens next doesn’t add to yield potential—it subtracts from it. That’s why Farm Journal Field Agronomist Ken Ferrie is quick to remind farmers that a corn plant should never have a bad day.
Getting corn off to a positive start requires placing seeds at uniform depth, closing the furrow and firming the soil, taking out air pockets so moisture cannot escape. At Farm Journal Corn College, Ferrie draws upon lessons from Farm Journal Test Plots field studies to explain how to set down pressure and select a closing system to help plants jump out of the ground with their yield potential intact.
Think of planting not merely as dropping seeds in soil but as creating a microenvironment for growth around every seed. The result of too much down pressure is similar to that of planting in wet soil, Ferrie says. The soil around the seed will be overcompacted, preventing uniform emergence and slowing early growth. Those late plants will lag behind all season long.
It also smears the soil along the sides of the trench. "Sidewall compaction is often thought of as a no-till problem," Ferrie says. "But you can get sidewall compaction in conventional tillage too, if you apply too much down pressure."
Excess down pressure causes scoring on the top of the furrow, which causes the furrow to open up, letting moisture escape, Ferrie adds.
Too little down pressure causes some seeds to be planted shallower than others, resulting in uneven emergence and lost yield potential.
Hidden yield robber. If your entire field looks the same (because plants in every row are showing symptoms), too much down pressure can become an invisible yield robber. The effects were evident when Ferrie compared 100 psi, 250 psi and 400 psi of down pressure in adjacent rows. The study included moldboard-plowed, vertical-tilled, strip-tilled and no-tilled soil.
The effects of excessive down pressure included delayed crown root formation after the soil cracked and separated. "Crown roots can’t grow in air," Ferrie says. "The roots stop growing and wait for you to throw some soil over them, or for rain to fall to wash soil into the slot and cover the roots.
"Plants with poor root systems want to tip over and lean in the wind. Eventually, there are big differences in plant height," he adds.
In the study, conventionally tilled ground needed the least down pressure and no-till needed the most. Finding the ideal down pressure for your soil conditions is more complicated.
No one intentionally applies too little or too much down pressure, Ferrie notes. But, in the stress of planting season, it’s easy to forget to consider the effects of tillage, planting speed and planter attachments and to make the necessary adjustments.
Speed kills. Speed might have the biggest impact on seed placement. "A farmer bumps up the throttle, then discovers seed depth is all over the place," Ferrie says. "That’s because his planter is bouncing up and down.
Instead of slowing down, he cranks up the down pressure. Then he gets sidewall compaction—it’s a chain reaction."
Poor seedbed preparation can also cause a frustrated operator to pour on more pressure. "Below the surface, soil density must be uniform," Ferrie says. "Tillage must be uniform, so you have 3" to 4" of uniform soil to plant in. If it is uneven under the surface, it’s like planting over speed bumps. Operators find uneven seed placement, then apply more down pressure to get through the rough spots."
- March 2012