Soil Moisture and Corn Seeding Depth

• Generally, 2-inch seeding depth for corn is optimal in most situations.
• Seeds should be planted in uniform soil moisture for even emergence.
• Increasing planting depth may be necessary to reach uniform moisture in dry soil conditions.

Corn Seeding Depth

Generally, seeding corn at a depth of 2 inches is optimal in most situations for multiple reasons. Soil moisture and temperature are often most stable at 2 inches. There is adequate space for proper nodal root development to help anchor seedlings. A 2-inch depth is also typically below the concentrated chemical layer, diluting herbicides, fertilizers and other inputs before encountering the seed and newly developing roots.

However, environmental conditions, especially soil moisture, are the ultimate driving factors in determining optimal planting depth. It is important for all newly planted seeds to evenly imbibe moisture within the first 24 to 48 hours to ensure uniform emergence. Adequate soil moisture at seeding depth is needed to ensure rapid germination of the seed. Soil moisture must be spatially uniform in the seed trench for even germination and emergence.

There are multiple reasons for never planting corn shallower than 1.5 inches. Uptake of water and nutrients through the roots is reduced with shallow-planted corn. Shallow-planted corn can also develop rootless corn syndrome where young plants will fall over due to the lack of nodal root development in dry soil conditions. It is necessary to increase planting depth to reach uniform soil moisture under such conditions. It is possible in some cases, where seeding depth was sufficient, that being planted in dry loose soil means the soil will compact after hard rains. This leaves the seed at shallower depths than when planted. Planting too deep may delay germination due to low soil temperatures and increased vulnerability to soil crusting, disease and insect pests. For these reasons, planting depth recommendations are typically 2 inches or greater.

After emergence, planting depth can be easily determined by measuring the length of the mesocotyl (area between the seed and crown) and adding ¾ of an inch. The nodal root area, or crown, typically develops about ¾ of an inch beneath the soil surface regardless of planting depth (Figure 1).

Agronomy in Action Research Trial

A corn seeding depth study was conducted at Clinton, IL, in 2022. Plots were planted at seed depths of 1.5 inches, 2.0 inches, 2.5 inches and 3.0 inches.

Clinton, IL, experienced optimal soil moisture and temperature at planting and for much of the growing season. The only period of moisture stress was during the V8-V12 growth stages. Due to the ideal conditions at planting, emergence and early-season growth, there was no yield difference between any of the 4 planting depths (Graph 1).

Early-season stand counts were taken and showed no significant difference in stand between seeding depths (Graph 2).

Summary

Planting at depths 2 inches or greater has shown to maximize yield most consistently in university and ag industry research trials. Many producers target 1.5-inch planting depths; however, slight changes in soil conditions and amount of residue on soil surface can quickly raise planting depths closer to the surface. Consistent seed depth starts with planter maintenance and soil preparation. Seed depth should be checked for each field. If soil conditions are variable for a given field, seed depths should be checked more often. Adjusting seed depth for the field characteristics is necessary for uniform emergence.