March 8 corn planted at either 1.5, 2.0, 2.5 or 3.0 inches deep – Effects on crop development and population

On May 17, Ryan Farmer, a student hourly worker at the Northwestern Illinois Agricultural Research and Demonstration Center (NWIARDC) collected stand count data from a demonstration trial that had been planted more than 2 months earlier. On an unseasonably warm March 8 day NWIARDC personnel decided to see just how wise it is to plant that early in the Monmouth area.

Needing to calibrate a new planter, they planted corn at a rate of 35,800 seeds per acre at four different seeding depths: 1.5, 2.0, 2.5 and 3.0 inches. While not exactly sure of what to expect as far as emergence and eventual plant stands, one may have suspected that there would be some differences when compared with seeds planted on a more 'typical' planting date. Those seeds planted at the shallow depths would be most able to take advantage of the warm day-time temperatures but would also be most exposed to the cold (or freezing) night temperatures. Conversely, those seeds planted deeper would be more insulated from these daily temperature fluctuations, but the emerging seedlings would have further to grow until they reached sunlight.

The typical corn planting date study at the NWIARDC targets the first week of April for the earliest planting date. In 2016, the first corn in this study was planted on April 5 at a depth of 1.75 inches and a seeding rate of 35,800 seeds per acre.

According to the daily high and low soil temperatures under bare soil at both the 2 and 4 inch depths, none of the seeds at any of the planting depths would have been exposed to temperatures below 40 degrees. The daily high temperatures were likely more damaging, as they were only higher than 50 degrees (the temperature that corn needs for growth and development and at which GDDs begin to accumulate) on 2 days during the first month after the March 8 planting. This is likely why, regardless of planting depth, the March 8-planted corn took about 7 weeks to emerge from the soil. Incidentally, corn planted on April 5 emerged BEFORE that planted on March 8.

Stands were also significantly negatively impacted by early planting, with emerged populations averaging 23,000, 25,000, 17,000 and 17,000 plants per acre at the 1.5, 2.0, 2.5, and 3.0 inch planting depths, respectively (Figure). Those March 8-planted seedlings that did emerge did so unevenly, with plants in each row having between one and two leaf collars. This uneven crop development can make plants that are not as far along act as weeds to adjacent plants that are more developmentally advanced, further reducing yield potential.

Weather data source: Water and Atmospheric Resources Monitoring Program. Illinois Climate Network. (2015). Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7495.