By Dennis Todey
As of the latest USDA-NASS report on Monday 20 July, 43% of corn had tasseled in South Dakota, which is ahead of last year and the 5 year average. That number will increase again next week with temperatures varying around seasonal averages over most of the state. Additional late week heat will continue to accumulate degree days. While the additional heat has been beneficial for the additional degree days, the heat has also started to introduce stress in corn in several locations. Most degree day accumulations in the state are close to average assuming reasonable planting date.
Stress Factors: Heat, limited precipitation & increased water use
The reason for the crop stress is not only the additional heat. Most of the temperatures have not reached well into the 90s, which would be expected to increase stress. Two additional climate impacts are at work. Large portions of the state have received limited or no precipitation in the last 2-3 weeks. With the early season moisture, the initial dryness was not an issue. Now the issue is starting to show up because of the increased water use that occurs during the reproductive stages of corn development. Corn uses the largest amount of water at this time.
During the cooler days in the early part of the month daily crop water usage could likely have been less than 0.2” per day. With the hotter temperatures in the middle part of the month that amount could reach a third of an inch or more, especially in the warmer/drier locations in the state. Data for Brookings estimates crop water use at over 4 inches for July. The water use was only balanced by 1.42 inches of rainfall.
Thus, corn is drawing into the soil moisture reserves everywhere in the state. Lighter soils with less soil moisture holding capacity likely will not have enough moisture to supply the full crop water need. Stress is introduced, starting to reduce yield potential.
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