The plant that we call corn can trace its history to a line of tropical grasses that grew in Central and Southern Mexico, where the sun routinely baked both the vegetation and soil from which it grew. This heritage helps to explain the plant’s ability to survive in a hot, dry environment.
Today, farmers can choose from a variety of hybrids genetically created to tolerate daytime temperatures up to 110 degrees or more for brief periods, with little to no effect on their overall health or photosynthetic processes.
But when the thermometer breaks into triple digits and stays there for multiple days in a row, with corresponding higher temperatures at night, any corn hybrid is going to suffer. Compounding the effect, these higher temperatures are typically accompanied by lower levels of soil moisture; evaporation from the soil increases, as does the corn plant’s process of transpiration or allowing moisture to escape through its leaves. The combined effect is called “evapotranspiration,” and it may cause the plant to speed up its development, producing less grain as a byproduct. This lowers the total yield at harvest.
Heat and Drought Concerns Aren’t Going Away
Discussions about heat tolerance and accompanying research are becoming more and more important as average temperatures rise year over year. According to a NASA study, corn yields are projected to drop 24% globally by the year 2030 thanks to higher temperatures, shifts in rainfall and higher concentrations of carbon dioxide at the surface. And this is at a time when a growing global population will need more food than ever.
How Corn Responds to Hot Dry Weather
Corn relies on photosynthesis and is very efficient at turning light and carbon dioxide into sugars. But as daytime temperatures rise, this efficiency decreases as the plant makes less sugar to use and store. If the temperatures stay high overnight, the respiration rate of the plant will increase, causing it to use or waste sugars for growth or development. This, in turn, reduces corn yield by reducing both the number of kernels and the weight of the individual kernels.
Corn plants are most susceptible to heat and drought stress at the V12 stage, roughly two weeks before silking. All the leaves are full-size, brace roots are developing, and the number of kernels per ear and size of the ear are still being determined. High daytime and/or nighttime temperatures, coupled with low soil moisture, can decrease potential yield by up to 4% each day. Should the severe stress continue through the silking and pollen shed period, the losses can be as high as 8% per day. Visibly, the leaves will begin to roll, and silks that emerge may dry rapidly, losing their receptiveness to pollen. Ears will develop shorter, with fewer and smaller kernels.
Fortunately, the modern corn plant is an extremely hardy specimen, with time-tested natural defenses against heat and drought that have been supplemented by modern science and genetic research. Plant breeders learn more every year about the pathways that plants use to defend against heat and drought. Through gene editing, breeders can “turn on” the genes that fight heat and drought in a matter of months, as compared to the years it would take through conventional breeding. Breeders are also working on ways to help plants use the higher concentrations of carbon dioxide found in the atmosphere today. The answer may be as simple as modifying the corn plant’s structure to reduce the amount of surface area that must be protected in hot and dry conditions.
Here are a few steps you can take to help ensure that corn plants are well-protected:
Choose hybrids tested for heat and drought. Most corn hybrids are evaluated for heat and drought stress tolerance. Choosing hybrids with higher drought or heat scores can protect the crop from wide temperature swings, ensuring vitality. There is no free lunch, however; defensive hybrids with the best protection against heat and drought stress often underperform in ideal conditions, yielding less than hybrids with no abiotic stress traits.
Use cover crops and residue. Western farmers know that it takes 10 inches of water to produce the first bushel of corn, so they must ensure every inch of rain gets “banked” into the soil. Cover crops, residue management and strip-tillage can all help reduce the amount of moisture lost to runoff or surface ponding in the fields. The residue allows rainfall to move into the soil and prevents soil moisture from evaporating by reflecting the sun’s rays, rather than letting the plant absorb them. The residue also acts as an insulating blanket over the soil, separating the soil from the warmer atmospheric air above it. The benefits of using cover crops and residue are easy to see in the heat of the summer. Soil temperatures are lower, more moisture is retained and the crop has more water.
Manage your crop in season. Abiotic stresses such as drought, salinity and temperature variance can quickly injure or kill growing plants. A foliar nutritional treatment can help.
Wait to plant until the soil temperature is right. Because it’s been getting warmer sooner over the last century, farmers have been able to plant sooner. This can be a tremendous advantage because early planting means the corn has more time to mature before harvest. But farmers should wait to plant into soil that maintains a continuous daytime temperature of 50 degrees or higher. That’s because new seeds start absorbing water—as much as 30% of a seed’s weight—in the first 36 hours after planting. If the soil temperature is lower than 50 degrees when this absorption begins, the seeds can be damaged, making them more susceptible to drought and disease.
Farmers with sandy soils are often able to plant earlier in the spring because the soil dries out faster but need to be aware that these same soils can cool rapidly; nighttime temperatures can quickly drop below optimum levels. Farmers can also hurt themselves by waiting too long before they plant. Consolidation over the years has increased the size of many operations, which can increase the number of planting days required. The optimum window for planting, however, is fairly small. Farmers are advised to plant earlier than later to capture as much of this window as possible, assuming that soil temperatures are 50 degrees or higher.
Check your soil’s fertility. One of the best defenses against heat and drought stress is soil fertility. This includes maintaining a proper soil pH greater than six and ensuring the plants have access to adequate supplies of potassium, calcium and micronutrients such as manganese. All of these nutrients combine to help activate the plant’s physiological processes to hold onto moisture and protect against heat stress.
Sprinkle regularly to beat the heat. In center pivot-irrigated areas, many farmers have been trained to use their sprinklers heavily, applying an inch or more of water at a time to help ensure that moisture is sufficient to reach the lower layers of the root zone. The theory is that deep moisture encourages deeper root growth. However, adding small amounts of water— ¼ to ½ inch at a time, for instance—can have a tremendous benefit in the early vegetative states when roots are developing. And during a heatwave wave, the same amount of water every three or four days can lower the soil temperature where the plant is developing. This, in turn, helps cool down the plant canopy and increases the plant’s metabolic functions in its reproductive stages.
Monitor for heat and drought stress. Farmers have several tools to monitor heat and drought stress. GIS tools can track moisture and temperature at the field level and estimate potential impacts on yield. Farmers with irrigation can use field sensors to track soil moisture depletion and change irrigation schedules on the go. Satellite or drone imagery provides a useful overview of how fields tolerate heat and drought stress. These abiotic stresses can reduce both yield and the crop’s standability. Getting the most out of this technology starts with field scouting. Seeing field conditions with your own eyes is essential to calibrating and using information technology.
Healthier Plants Are Hardier Plants
Agnition’s proven line-up of crop health solutions can help your crop use nutrients more efficiently, improving plant processes such as early growth, plant defenses and photosynthesis.
Plants that start ahead tend to stay ahead the entire growing season- and are better equipped to withstand seasonal stress.
Contact us to learn more about what Agnition can offer your farm!