Choice of seeding depth for corn is often paid scant attention by growers during the rush of planting their crop.
Human nature being what it is, we tend to simply leave the planter’s depth control setting at the same position as in previous years.
Indeed, many agronomists agree that a seeding depth of 1.5 to 2 inches is a fairly all-purpose range that works well in most situations. However, certain conditions merit consideration of changing seeding depth, the most common of which is soil moisture at seed depth.
Adequate soil moisture at seed depth (not too wet, not too dry) helps ensure rapid germination of the seed. Equally important is the spatial uniformity of adequate soil moisture at seed depth because that influences the uniformity of germination and subsequent emergence of the crop.
The importance of the adequacy of soil moisture at seed depth is highlighted by the fact that imbibition of moisture by the newly planted seed occurs with the first 24 to 48 hours after planting.
Many growers have taken advantage of the unusually warm temperatures and minimal rainfall in recent weeks to complete their pre-plant tillage operations, herbicide applications, and nitrogen fertilizer applications. The completion of those activities certainly lends optimism that corn planting in 2012 will proceed at a rapid pace over the coming weeks if the weather continues to cooperate.
However, “cooperation” of the weather includes the absence of any significant rainfall that would delay planting. Therein lies the challenge this year in choosing the proper seeding depth because soil moisture near the surface is already borderline adequate for seed germination in some fields.
Planting corn at the usual 1.5 to 2 inch seeding depth may place seed into soil too dry for germination or (even worse) into soil that is unevenly moist that will result in uneven germination and emergence.
If rainfall remains a scarce commodity over the coming weeks, growers should assess soil moisture at seed depth in every field they plant. There will be situations where a 2-inch seeding depth does not provide uniformly adequate soil moisture. There will be situations where growers should place seed deeper to minimize the risks of uneven germination.
Remember This: Corn has the physiological capability of emerging from depths far greater than that which today’s planters can place seed because of the innate ability of the seedling mesocotyl to elongate during the emergence process.
Soils in some fields are prone to developing dense surface crusts following intense rainfall events that can interfere with seedling emergence and result in seedlings leafing out underground. Growers naturally hesitate to plant too deeply in these soils because of this risk.
My opinion is that the consequence of surface crusting is mostly influenced by the timing of the development of the crust relative to the timing of the emergence process and less so by the depth of seeding. In other words, a dense surface crust can impede penetration of the seedling coleopile whether the seed was planted 1.5 inches deep or 3 inches deep if the crust develops shortly after planting.
Field to field variability for adequacy of seed depth soil moisture may be dramatic this year. The risk/benefit of deep seed placement is influenced by the depth where adequate soil moisture is spatially uniform, soil temperature at seed depth, and the 6- to 10-day forecast for rainfall and temperature.
A combination of 1) adequate soil temperature today, 2) inadequate or variable soil moisture at 2 inches, and 3) little to no rainfall expected in the next week or two represents a planting situation that calls for choosing a seed depth deeper than 2 inches.