Farmers who planted corn after mid-May said they usually set it two inches deep. Some wondered if that was too deep, but reports say that it came up quickly and uniformly. Don't hesitate to go as deep as you want. The corn can push up through the soil and emerge. Going deeper guarantees that you access moisture, and the temperature at that level now is far over the 55 degrees F needed for corn to germinate.
(originally posted March 29, 2010) Dave Nanda, Indianapolis, has worked in plant breeding or more than 40 years. He has also interviewed farmers who do a good job of obtaining good stands of corn. And he's talked to some who don't do such a good job of getting cornfields to emerge evenly and uniformly. Surely over 40 years he's learned a few things about what makes the difference between obtaining good stands and average stands.
Part of the answer is in choosing the right seeding depth, Nanda says. Hardly anyone would only plant one-half inch deep. It's simply too shallow for rooting, and germinating seedlings that close to the surface could run out of moisture. The more common placement is either one or 1.5 inches deep.
However, Nanda says many farmers still plant at least 2 inches deep. That seemed to be the standard in the old days, before no-till and minimum tillage planting, and is still the depth of choice if the soil is dry and the forecast calls for more dry weather ahead.
Barry Fisher, state agronomist with the Natural Resources Conservation Service, sees a problem with going that deep in most no-till situations. If you're trying to plant early enough to get in on the higher yields that usually result from earlier-planting dates, soils are likely to still be cool and moist at deeper depths, especially in no-till situations. No-till fields warm up slower because residue covers the surface, keeping soils cooler and wetter.
The other problem, he notes, is that you're likely to pull up more moist soil. Fertilizer coulters, especially ones with notched blades, are notorious for throwing out moist soil that then sticks to gauge wheels, he notes. Pretty soon your planter is not operating as smoothly as it was set up to do. The result can be uneven depth placement.
If one seed is placed at 1.5 inches deep and the other at 2 inches in no-till, there could be a sizable temperature difference, he notes. That could determine how quickly each plant emerges. If the deeper one is several days slower in maturing, it may act like a weed he rest of the season, and perhaps not produce an ear. Instead of a productive corn plant, it becomes a weed competing with plants that are producing ears for sunlight, moisture and nutrients.
Both Nanda and Fisher believe consistent seed depth placement is crucial, and is worth the effort it takes to make it happen. It will also be worth the extra time it takes to stop and dig, row by row, until you're satisfied that your planter is placing seed at a depth that is as consistent as possible.