Earlier this summer, more than 44% of the United States was in a moderate to exceptional drought, according to the U.S. Drought Monitor U.S. Drought Monitor. And while some late-summer heavy rains have helped farmers across much of the Corn Belt, farmers across Texas and parts of California and the rest of the Southwest were still dealing with extreme drought conditions in early September. As harvest approaches, how do you know whether periods of drought will affect your fall yields?
“The impact that drought has on corn yield loss really depends on what crop stage your corn was in when drought occurred and how long it lasted,” says Todd McRoberts, NK Seeds Agronomy Manager. “Drought during an early growth stage should have minimal impact on yield, since water demand is low at this time, while drought just prior to pollination and in weeks following can have a significant impact since this is when peak water use occurs.”
Early-season drought stress reduces secondary root development and leaf size, and it often contributes to fewer kernels being formed per row during ear development. Pollination drought stress is marked by a delayed tassel emergence, which can lead to basal and top kernels not pollinating. Finally, late-season drought stress compromises root and stalk health, along with an increased abortion of kernels and a reduction of kernel size and weight.
Research has shown that drought stress during pollination can cause up to a 50% yield loss, whereas drought just before or just after this stage can cause a yield loss of 20%-25%.1 What are visual clues to look for to determine if your corn plants have been affected by drought?
Three Signs of Drought Stress
- Rolled plant leaves.
“Drought reduces transpiration, which causes the plant to conserve moisture as a defense mechanism,” says McRoberts. “This induces a rolling of plant leaves, and if it persists for more than 12 hours in a day, some grain yield loss is likely.” (Leaf rolling for a few hours during the heat of the day is not likely to cause yield loss.)
- Reduced secondary root development.
Your late-season root digs may show the aftermath of an early-season drought in the form of reduced secondary root development. Nitrogen and potassium deficiencies are commonly both seen in drought-stressed corn, according to McRoberts. “Reduced secondary root development may reduce the plant’s ability to mine the soil for moisture and nutrients,” he warns. “You may therefore observe signs of nitrogen or potassium deficiencies even though there is plenty in the soil.”
- Poor grain quality.
Photosynthesis reduction caused by drought may limit the plant’s ability to produce the sugars and starches needed to develop grain. This can result in poor grain quality and reduced yield potential.
In a matter of weeks, farmers will see for themselves what impact this season’s drought may have had on their yields. While the yield numbers remain to be seen, one thing is for certain: no matter the results on this year’s yield monitors, corn and soybean farmers will take it in stride and look ahead to a fresh slate for 2023.
Look for more seasonal agronomic tips here on The Amplifier throughout the growing season.
1Denmead, O. T., and R. H. Shaw. 1960. The Effects of Soil Moisture Stress at Different Stages of Growth on Development and Yield of Corn. Agron. J. 52:272-274.
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