A corn plant requires the accumulation of Growing Degree Units (GDUs) to reach maturity. This is regardless of the number of calendar days it takes to accumulate them. A 105-day hybrid requires about 2600 GDU’s to reach Black Layer and a 114-day hybrid requires about 2800. You can use this information to your advantage because we know about how many GDU’s need to accumulate for each growth stage. In other words, if you know the planting date, we can predict when the hybrid will pollinate. This can help growers make timely applications of herbicides and fungicides. Also, it can predict when optimum timing is for foliar fertilizer applications.
To calculate GDUs, record the minimum and maximum temperatures for the day. Add them together and divide by two. Next subtract the base threshold of 50 degrees F. Because optimum corn growth takes place between 50 degrees and 86 degrees F, the lowest temperature that can be used in the formula is 50 degrees F, and the highest temperature is 86 degrees F. A typical calculation for April in Central Ohio looks like this: ((68 + 50) / 2 ) – 50 = 9 GDUs.
During April, several counties like Preble, Darke, Champaign, and Shelby planted some corn acres on the 21st. Based on this planting date and an average of 8 GDUs accumulated per day, we can predict that corn emergence will be on May 5 to 6, or in about 14 to 15 days.
In these counties that planted on April 21, soil temperature reached 60 degrees F. Certainly, that is good enough to trigger germination if moisture is adequate, but it will be interesting to see if these plant stands are good enough to keep after the rainfall event that occurred on April 25. That rainfall was cold and as low as 44 degrees F. I measured the rainfall water temperature at several locations.
If seeds imbibe cold water or experience cold temperatures in the first few days after planting imbibitional chilling injury can occur. This may result in failed germination or poor early growth of the seedling. Chilling injury during the emergence process can result in corkscrewed mesocotyls or leafing out below the soil surface. Field conditions that create chilling injury include extended exposure to soil temperatures under 50 degrees F. If the rainfall event is cold enough it may drop the soil temperature down below 50 degrees F. The soil temperature at planting may have been ideal but the cold rainfall dropped it below the minimum to trigger germination. Minimum soil temperature for corn germination is 50 degrees F and soybean requires a soil temperature of 55 to 60 degree F.
Emergence and stand establishment (VE – V8)
High corn yields come from a perfect uniform plant stand where all of the plants emerge at exactly the same time. This is not a secret. A corn seedling that emerges 2 days late can cost you about five bushels per acre. Crop scouting at this time of the year can provide some clues as to what to expect for yield potential. As seedlings emerge and begin their growth process, it is important to know what to look for.
When plants develop two to three leaves, conduct plant population counts to determine the quality of your stand. Take note of doubles and skips in the sample. Dig where the skips occur to see if a kernel is present and note its condition.
Measure the planting depth by using a trowel to carefully remove a seedling with the roots intact. Locate the mesocotyl, which is the area that extends between the seed and the point where the permanent nodal roots are forming. Adding approximately three-quarters of an inch to the length of the mesocotyl gives an estimate of the planting depth. Uneven seeding depth exposes deeper planted seeds to slightly cooler seed zones than shallower placed seeds and can lead to uneven emergence. Measure planting depth in several areas and note the range of depths. Take your observations into consideration when planning for future plantings to help ensure your best chance for top end yield potential.
Early Season Corn Growth Stages
|VE||100 to 130 GDUs||Plants emerge|
|V1-V2||7 days after|
|Second leaf develops, about a week after emergence|
|V3-V5||280 GDUs||Potential number of|
leaf and ear shoots
|V6-V8||400-650 GDUs||Growing point is above the soil surface|