Spring 2020: Heating Up

Some areas of the corn belt experienced good field conditions in late March and early April that allowed for fertilizer applications, burn down spraying, and other field preparation. In many areas, conditions were very tempting for planting but the temperatures and the calendar were a concern.  In the southern part of the region, some corn acres were planted during the first week of April with additional acres planted about two weeks later. Just as spring looked to be well on track, along came the cold nights in early May with widespread freeze damage for many growers.

If we take a closer look at the development of a corn crop, assuming a planting date of April 20 and moving to the present date of May 25, average growing degree unit accumulation for central Indiana would be about 11.8 units/day. Over that time period, we would be approaching a total of 413 units. In 2020, according to the University of Illinois heat unit calculator, Hendricks County Indiana near Indianapolis has only received 4.2 heat units/day during that period and we are now at a deficit of 265 heat units compared to the 30 year trend line.

The following diagram tracks heat unit accumulation in 2020 on the black line compared to the 30 year average plotted in purple.  The data would indicate corn planted April 20 at this location emerged in about 17 days on May 6 and at the present time crop development is tracking about 15 days later than normal.  The delayed emergence might have caused some minor stand loss and the reduced leaf area, and  transpiration rate. In addition, reduced root mass due to the delayed development may limit nutrient uptake rates until temperatures return to a warmer seasonal pattern.  Mineralization of soil organic matter will occur at a slower rate and subsequently availability of mineralized nitrogen, sulfur, and boron may be observed.

Post emerge herbicide applications may be pushed a few days later than normal and weed development will also be delayed by the cooler temperatures, and extra care will be needed to properly time these activities for best weed control.  Rapid growth phase of the crop and maximum nutrient uptake may be slightly later than normal, depending on temperatures moving forward.

The next diagram shows how the crop might progress with a return to normal 30 year trend GDU accumulation.  Warmer, sunny days ahead may allow the crop to return to a more average rate of development.

University of IL Growing Degree Calculator

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