The heat experienced in Kansas recently can cause problems for all summer row crops. With corn, the latest Crop Progress and Conditions Report from USDA-NASS, July 10, 2017, shows that the crop has already reached more than 40% silking, except in the western districts. At this point, high heat could have an impact on abortion of early-formed grains and also abort more susceptible kernels already formed in the tip of the corn ears. High heat at this point could also impact pollination across the western section of the state. Overall, temperatures above 95 degrees F (Figure 1), and more importantly lower fluctuations in the difference between day and night temperatures (diurnal temperatures, Figure 2), will have a critical impact on kernel number (abortion process) and on the duration of grain filling (occurring now in southeast Kansas), consequently impacting final kernel size/grain weight.
Figure 1. Total hours with average air temperature greater than 95 degrees F from July 7 to 13.
Figure 2. Weekly average diurnal (max – min) temperature variation for July 5 to 11.
Heat stress will have more of an impact on corn at this stage of growth when combined with drought stress. For the July 5-11 period, precipitation amounts have been erratic with adequate (1 inch or more of rain) in the eastern and part of the western areas of the state. A large departure from the normal precipitation was recorded in the northeast, north central, and east central parts of the state, with approximately an inch less rain than normal during this period (Figure 3).
But even when drought stress is not an issue, heat stress alone will increase the mismatch between pollen shed and silk extrusion when corn reaches flowering. The potential for yield reductions around pollination are quite high, diminishing as the crop progresses into later stages (blister and milk stage).
Figure 3. Weekly precipitation summary (upper panel) and departure from normal weekly precipitation (lower panel) for July 5-11 period.
For soybean and sorghum, heat stress could also impact plant growth and maximum yield potential but the risk is less than for corn at this point in the season since soybeans and sorghum are not yet in the high-water-demand period (pod formation for soybeans and flowering for sorghum). Based on the last Crop Progress and Conditions Report from USDA-NASS (July 10, 2017), soybeans are just blooming (27%) and sorghum is only starting to head (4%). These crops would have a higher level of risk of yield reductions due to high temperatures, combined with drought stress, if the timing of the stress were to occur toward the end of July to mid-August.
For more information on summer row crops growth and development and production management, visit all K-State and KSUCROPS Lab publications:
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist
Mary Knapp, Weather Data Library