Soil moisture levels and uniformity at planting depth can determine how rapidly and uniformly seeds germinate and eventually emerge. Even so, farmers often are content to leave planters set to the same seeding depth as the previous year - something Bob Nielsen, a Purdue Extension agronomist, says they might want to reconsider.
"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," he says. "However, certain conditions merit consideration of changing seeding depth, the most common of which is soil moisture at seed depth."
The recent warm, mostly dry weather have helped farmers to complete tillage and herbicide, nitrogen and fertilizer applications, and have sparked optimism about a rapid planting season. In order for that to occur, there would have to be little significant rainfall, which Nielsen says reinforces the need to reevaluate seeding depth.
"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," he says. "Planting corn at the usual 1.5- to 2-inch seeding depth might place seed into soil too dry for germination, or even worse, into soil that is unevenly moist and that will result in uneven germination and emergence.
"There will be situations where growers should place seed deeper to minimize the risks of uneven germination."
Nielsen says it's important to remember that corn is capable of emerging from planting depths much greater than what planters can even plant.
Part of the reason farmers hesitate to plant too deeply has to do with the fact that soils in some fields can develop a dense surface crust after heavy rain. That crust can interfere with emergence, and could even lead to seedlings that leaf out underground.
"My opinion is that the consequence of surface crusting is mostly influenced by the timing of crust development relative to the timing of the emergence process, and less so by the depth of seeding," Nielsen says. "In other words, a dense surface crust can impede penetration of the seedling whether the seed was planted 1.5 inches deep or 3 inches deep if the crust develops shortly after planting."
Something else farmers need to consider is that adequate seed depth could vary widely this year. Nielsen says the risks and benefits of deep seed placement are influenced by the soil moisture uniformity and temperature at the seed depth, and the 6-10-day rainfall and temperature forecasts.
A combination of adequate soil moisture now, inadequate or variable moisture at 2 inches and little or no rainfall expected in the next couple of weeks suggests a seed depth greater than 2 inches might be warranted.