Some very cold planting season temperatures have growers anxiously awaiting corn emergence. Generally speaking, it takes 150 to 180 crop heat units (CHUs) to get corn from planting to emergence. Soil texture and moisture content, residue cover, sunshine intensity, and planting depth can all impact how quickly the CHUs (measured with air temperatures) can translate into successful germination and emergence.
The Ontario CHU calculation needs a minimum daytime temperature of 10 degrees C or a minimum nighttime temperature of 4.4 degrees C before CHUs are counted. Table 1 shows the temperatures (both recorded and forecasted) and CHUs for London this spring. It will be no surprise to anyone that we have had quite a few days that recoded a zero for heat unit accumulation.
Figure 1 takes the London temperature data and puts it in a graph showing CHU accumulation (actual and estimates) for the period April 16 to May 30. On the graph, we indicate three planting dates and estimated the emergence date for each. Estimated emergence dates were based on accumulating at least 165 CHUs. Although this data will not necessarily reflect your area, farm, or soil type, it can give you a ballpark estimate of emergence timing.
Although we often expect corn to emerge most years in 10–15 days, some of the early planted corn this year is going to need longer, in the range of 21–25 days. For example, corn planted on April 25 is estimated to emerge on May 19 (24 days). Most of this corn was planted in excellent soil conditions—cold but very fit—which bodes well for successful emergence. At Maizex, we did have some concern that very cold temperatures combined with rain or snow might have shocked the corn seed (imbibitional chilling) that was planted just ahead of these weather conditions and caused uneven emergence. However, dry conditions that prevailed through much of this cold planting window certainly lessened the risk to the seed.
Some photos of corn seedlings from various planting dates and locations are included in Figure 2. Assessing corn emergence is a great tool in evaluating your potential corn yield and for troubleshooting planter problems and/or soil preparation or weather impacts on the crop.
At Maizex, we believe that conducting a Corn Stand Audit in or around the middle of June can really help this process. In the Maizex Corn Stand Audit, we assess population, planting depth, uniformity of spacing, and uniformity of emergence and early growth in the crop. Combine this information with a final ear count and you have some powerful tools to move corn management and yields to the next level.
Please contact your Maizex representative if you have any questions about information in this article.