04/29/2025
Why can’t farmers in Memphis, Texas, produce corn? This is a question I often ask at different times throughout the season. The answer is always the same…”It is too hot to grow corn in Memphis, TX.”. While soil health can play a role, adverse climatic conditions are primary reasons corn is not produced in this area. Heat, drought, and arid conditions in the summer months are huge factors preventing corn production for our neighbors to the east. Figure 1 shows historical high and low temperature comparisons for Memphis and Dimmitt. There is a clear delineation in daily high temperatures from June 20 to August 15 (pollination window) between the locations. Based on historical averages, night temperatures between the locations are more important when considering corn pollination and fertilization. In Dimmitt, historical data shows summer night temperatures in the low sixties allowing corn to rest thereby conserving sugars that are important for pollen formation, pollination, fertilization, and kernel development. Conversely, Memphis’s night temperatures are close to or exceed 70° F. Night temperatures hovering at or above 70° F increases plant respiration. Increased respiration increases plant water use and burns sugars that would be used for pollen development. These factors can reduce or prevent pollen formation and negatively impact pollen viability.
Over the past few years, corn pollen shed in many corn fields in the southern TX High Plains has been minimal resulting in slow pollination/fertilization or incomplete pollination. Reasons around reduced pollen shed are generally caused by adverse climatic conditions (heat, low relative humidity, and drought) during pollen development and pollen shed. Other potential and compounding issues will be discussed but increasing temperatures is likely the leading contributing factor in reduced pollen development/pollen shed. Figure 2 illustrates the same historical information in Figure 1 with the addition of the average high and low temperatures for Dimmitt over the last ten years (2015 to 2024). There is a trend toward higher day time temperatures over the last ten years. The two week period between July 8 and July 22 are the most extreme increase in daily high temperatures rivaling historic daytime high temperatures in Memphis.
Changes in overnight low temperatures for Dimmitt illustrates an extreme shift in night heat equal to historic overnight low temperatures in Memphis (Figure 2). This shift toward higher night temperatures was not influenced by one or two years. Changes are consistent across the past ten years. Higher night temperatures increase plant water use, increases respiration throughout the night, and expends sugars important for pollent development, viability, and silk viability (https://agcrops.osu.edu/newsletter/corn-newsletter/2019-27/hot-night-temperatures-can-decrease-corn-yield #:~:text=Breadcrumb%20Menu,Insight%20article%20referenced%20below%20concludes%E2%80%A6.).
In recent years, summer night temperatures are slow to decrease. Summer temperatures in excess of 90° F late in the evening are common. Early morning temperatures (between 3:00 and 4:00 a.m.) often exceed 70° F and moore typically range from the mid-70’s to low 80 degree ranges. Consequently, excessive night heat causes corn to burn stored sugars important for normal reproductive development.
In 2022, excessive heat (ambient and solar heat), wind (day and night), and low relative humidity the first three weeks of July resulted in missed corn pollination across the Texas High Plains. Heat during pollination has become more of an issue for corn production in the Texas High Plains. This has influenced some farmers to seed corn later in the season to avoid extreme heat when corn is shedding pollen. Does moving the planting dates really influence heat during pollen shed? My initial thought was “probably not”. Let’s explore factors influencing daytime ambient temperature.
Solar heat is strongly correlated with the sun’s angle to the earth. A more direct angle (on the summer solstice) concentrates solar energy into a smaller area. Think of this as holding a magnifying glass directly over and object. Concentrating light directly over the object will heat it up. Changing the angle of the magnifying glass scatters the light and it will be absorbed. So, as the earth tilts away from the sun following the summer solstice results in shorter day lengths and, generally, cooler temperatures (especially as it relates to solar heat). As the angle of the sun becomes lower, sunlight travels a longer distance and causes light to be scattered and absorbed. This reduces the amount of solar energy that reaches the earth’s surface.
Corn that is pretassel and tasseling on or close to the summer solstice is subjected to intense solar heat that may interfere with pollen development and viability. This issue is compounded where water for irrigation is limited. The heat (ambient and solar heat) causes plants to use more water. This usually creates water deficits causing leaves to roll and/or stomates to close. Upper leaves surrounding the tassels may trap heat where tassels are developing pollen. Extreme heat (ambient and solar heat) will kill developing pollen. Corn seeded later in the season will initiate reproductive development in late July or early August. The sun’s angle lower on the horizon will scatter light. Reducing solar heat removes a heat sink that could impact development and viability of pollen.
It is no secret that our aquifer is declining at an alarming rate. When water for irrigation is adequate or limitless for irrigation, it can not only be used to maintain soil moisture for corn growth and development, but it also helps manipulate the microclimate within a field. Corn fields where water is not a limiting resource can be characterized as humid and cooler than the air outside the field. As water becomes limited, evaporative cooling declines. Combining increasing ambient temperature (especially night temperatures), solar heat, and a declining aquifer creates an inhospitable environment for corn production (think of conditions that limit corn production in Memphis, TX).
Moving forward, corn production in the Texas High Plains will be possible but hybrids grown will need to have a strong combination of heat and drought tolerances. Manipulating planting dates will also be important to limit the impact of solar heat during reproductive development. The one big wild card will be increasing ambient temperatures, more especially night heat. Many sources agree that ambient temperatures will continue to increase over the next 20 to 40 years. This will challenge corn breeders (and most other spring seeded crops) to develop hybrids and varieties more tolerant to changing environmental conditions in our area.
