Source: Dan Quinn, Ph.D., Purdue University
During the heat of planting, one thing that often can be forgotten is thoroughly checking and understanding two items, 1) what seed depth am I planting at? and 2) is my seeding depth consistent, especially across all of my individual row units? We may often be inclined to use the “set it and forget it” approach to seed depth, yet this may not always be the best idea. In order to get corn started off on the right foot, it is important to achieve both rapid and consistent emergence following planting. One aspect of achieving rapid and consistent plant emergence is by choosing the correct seeding depth and ensuring there is adequate and uniform moisture at the chosen seeding depth. The most common seeding depths recommended for corn range between 1.5 and 2 inches deep, and these planting depths can work very well within most conditions, however, certain soil moisture conditions at planting may warrant further examination/change in seeding depth.
A corn seed imbibes soil moisture within the first 24 – 48 hours after planting, therefore maintaining both adequate and uniform moisture at seeding depth (not too wet and not too dry) within the first 48 hours is important. If the soil remains too dry, then the seed may be delayed in emergence until precipitation occurs. Furthermore, if the soil remains saturated after planting, the seed may rot and die. If the soil conditions are dry at planting, then a seeding depth of 2 inches may be too shallow and not place the seed in adequate/uniform soil moisture conditions. Therefore, if the moisture at a 3-inch depth is more adequate and uniform, and no additional rainfall is expected in the next week, then it may be worthwhile planting the seed at a 3-inch depth instead of a 2-inch depth. It is important to remember that corn can physically emerge at seeding depths lower than 2-inches, therefore, planting deeper can help ensure more consistent plant emergence when soil moisture conditions are dry. However, if soil moisture conditions are adequate it is likely ideal to not go much deeper than 2 – 2.25 inches. If planted too deep and soil moisture conditions are adequate, emergence can become delayed, thus further exposing the corn seed to various stresses (e.g., disease, insects, etc.). Furthermore, if corn is planted too shallow <1.5 inches, you can run the risk of poor root development, stand establishment, and lodging.
To further examine the impact of seeding depth on corn emergence and yield, a research trial was established at the Throckmorton Purdue Agricultural Center in Lafayette, IN. The research trial examined corn seedling emergence timing and yield differences across four different seeding depths and two different hybrids. The trial was designed as a randomized complete block design with three replications. Plots measured 30 feet wide (12, 30-inch corn rows) by 400 feet long and the center six rows were harvested with a commercial combine with a calibrated yield monitor. Trial results are presented below: