By Gregory Luce, Agronomist
There are a lot of factors that influence corn stand and final yield. Some we cannot control and some we can. One easy way to give your corn crop the best opportunity for consistent stand level, and ultimately yield potential, is to plant at the proper depth.
The old rule of thumb (index finger in this case) is to plant corn seed at a depth equal to the second knuckle on their index finger. Well, not everybody has the same length fingers so a bit more accurate measurement is in order for this important management decision.
University Extension publications across the Midwest typically recommend a corn seeding depth of 1.5-2.5 inches. Most agronomists will agree that planting corn too shallow leads to more frequent problems than planting too deep. From my experiences, bad things happen when corn seed is planted shallower than 1.5 inches. Therefore, I recommend targeting 2 inches as an excellent depth for corn planting.
A primary reason to target a 2-inch depth is to achieve good seed-to-soil contact. In order to accomplish this throughout the seedbed, the seed needs to be where the moisture levels are most consistent. Uneven soil moisture throughout the seed zone is the primary cause of uneven emergence, which can easily cause 8-10% in yield loss.
The second reason for the recommended planting depth is to establish a strong nodal root system.The nodal root system not only helps support the corn plant structurally, but is also responsible for uptake of the vast majority of the water and nutrients the plant needs. A good nodal root system is essential in reducing early season root lodging, as well as helping the plant perform better under drought stress later in the season. A shallower planting depth, especially less than 1.5 inches, can lead to early-season root lodging due to shallow nodal root development or corn injury from pre-emergence herbicides.
There are always exceptions to the rules that can rely on some fine tuning. For instance, if soil conditions are dry at planting time, planting to moisture is often practiced to help uniformity of emergence. Soil texture is another factor to consider. In very heavy textured, high-clay content soils, corn seeds should not be planted deeper than 2.5 inches. However, in lighter sandy soils, planting 3 inches deep may be necessary. In fact, planting 2.5-3 inches is recommended in states to the west of Missouri.
The conditions of every one of your fields may vary dramatically enough to warrant a slightly different seeding depth for each one. Growers should check corn seeding depths when they enter fields with different soil types or tillage practices. It is a recommended practice to spend some time evaluating each field at the time of planting.
In summary, corn should never be planted less than 1.5 inches deep, 1.75- 2.25 inches is an ideal target, but depending on soil type and conditions, may be planted up to 3 inches deep without any effect on stand establishment.