At an Oklahoma State University research plot, Brian Arnall showed us corn planted at four different depths: 5, 6, 7.5 and 10 centimeters, or approximately 2, 2.4, 3 and 4 inches.
Until recently, 5 centimeters was considered a normal planting depth for local farmers. Most tended to plant at 6 to 6.5 centimeters. Now the recommendation is gradually shifting toward 7.5 centimeters.
The trials show that corn can also perform quite well when planted 10 centimeters deep.
At first, this may sound almost like a recommendation to plant corn at 10 centimeters. But Brian immediately clarified that the trial was not designed to establish this depth as a new recommendation.
His point was different: if the moisture is deeper in the soil, farmers should not be afraid to plant deeper.
Yes, emergence may be delayed by two or three days. But the seed has more reliable contact with moisture, while the brace roots, sometimes called aerial roots, develop closer to the soil surface or even below it. According to Brian’s observations, these plants look healthier and cope better with drought and high soil temperatures.
Deeper planting does not necessarily increase yield. But Brian says it can make yields more consistent when the upper soil layer becomes hot and dry.
Interestingly, this pattern was first observed after the corn had been planted with a regular planter. The researchers then repeated the experiment by hand. They opened the seedbed to a specified depth, placed each seed and closed the row. This allowed them to eliminate planter variability and compare the different depths more accurately.
What interested me most in this conversation was not the 10-centimeter figure itself. It was our tendency to consider a particular planting depth correct simply because it has been used for many years.
Perhaps planting depth should be determined not by habit, but by where the moisture remains in the soil that year.