Environmental conditions across regions have been a concern recently with regards to crop growth. It is important to understand what potential implications these conditions may have on the crop and yields. The U.S. Drought Monitor and recent reports from several areas across the state have reported abnormally dry or worse conditions this month (Figure 1).
Figure 1. U.S. Drought Monitor for Ohio as of August 20, 2024. Source: droughtmonitor.unl.edu.
Drought and High Temperature Effects
Corn yields can be affected by drought; among cereals, corn is one of the most sensitive crops. Weather extremes, particularly drought and heat, pose significant challenges to farmers. Seasonal air temperatures and precipitation may explain about 30% or more of the year-to-year variability of crop yields in the largest crops, including corn. Corn has shown a negative yield response to higher air temperatures. These lower yields have been offset (at least partially) by introducing new genetics, agronomic strategies, and technologies.
Current weather forecast are not very optimistic, and we can continue to see some crop stress in fields. It is expected (and has been observed) that many fields, especially across western and northern Ohio, are still okay given good soil moisture levels below the surface from past rains. Most of our corn fields in Ohio are at the dough (R4) and dented (R5) stages. The highest water use in corn is around the tasseling (VT) and silking (R1) stage with about 0.3 inches of water per day. The corn water use rate between dough and dent stage is estimated at about 0.20-0.24 inches per day. Water use decreases from this point forward as corn gets closer to maturity. Learn more about corn water use here.
Implications in Corn Yield
If prolonged heat and drought conditions exist, crop yields can be affected primarily by:
1. Reducing number of kernels per ear (kernel set issues and kernel abortion). The success of pollination, kernel fertilization, and kernel retention determines the actual number of harvestable kernels through about R3 (milk stage). Normal ears have the potential to produce about 800 to 900 kernels. However, pollination issues or kernel abortion during grain formation will lead to lower numbers. By the R3 stage, the kernels that will continue to fill will increase in depth and those that were pollinated but aborted will appear yellow and will begin to shrivel. Large issues with unpollinated ovules or aborted kernels suggest stress during the VT/R1 (tassel-silking) to R2 (blister) growth stages.
2. Reducing kernel weight (or so called lower test weight). Kernel weight is determined during the latter half of the season from about R2 (blister stage) through to R6 (right before physiological maturity or black layer). Ears with low kernel weight would reflect conditions during the second half of the reproductive stages (R3 to R6). At this time, moisture in the grain is going down, while dry matter accumulation is going up. Approximately 40-45% of grain weight is gained during the first half of the dent stage (R5) alone. By R6 (physiological maturity), kernels have no longer milk line and have reached maximum dry matter.
Final Considerations
In the absence of drought/heat stress, other considerations include that modest increases in temperatures can increase growing degree day accumulation, which positively affects crop growth, development, and yields. An example of that is the more rapid progress seen in 2024. Given crop progress over this season plus the dry conditions faced in some areas now, it is expected that crops will mature and be harvested earlier this 2024 season.
The shift toward longer growing seasons (warmer temperatures) provides corn growers with an opportunity to increase yield and profits by selecting hybrids with later relative maturities or greater growing degree day requirements, particularly in northern US.
Some resources that can help to sort out the management or stress and timing that can impact corn yield are available here 1) Assessing yield-limiting factors in corn, 2) troubleshooting abnormal ears, 3) incomplete kernel set and tipped-back, 4) arrested ears, and 5) other ear abnormalities.
Agronomic decisions that could be used to lessen the effects of drought and high temperatures in corn production in future years are summarized in Table 1. One caveat is that these decisions need to be made prior to or at planting and cannot be implemented later in the season. These practices may be worth examining in future years to help offset some of the stress and potential yield loss caused by drought and heat conditions.
Table 1. Drought and high temperatures in corn production - summary of potential management decisions and challenges with their implementation. Source: Ortez et al., 2023.
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Management Decisions |
Challenges with their Implementation |
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Minimize the occurrence of stress during the kernel set period to optimize plant growth rate and ensure kernel numbers are preserved through varying hybrid-relative maturities or planting date variations. |
It is unclear when stress occurrence will appear within a season, and the critical period is long (one week before to three weeks after silking). |
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Drought-tolerant hybrids can produce a 15–45 bushels-per-acre yield increase relative to drought-sensitive hybrids if drought conditions exist. On the other hand, drought-tolerant hybrids can have 5–15 bushels-per-acre lower yield relative to the standard hybrids when hybrids are grown under adequate moisture. |
Higher yields for drought-tolerant hybrids have not been consistent or have been negative at times. Yield advantage of drought-tolerant inconsistencies have been partly attributed to different yield levels or actual water availability. |
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Conservation tillage has been largely recommended for goals related to soil conservation, water management, and building soil organic matter, which are all critical aspects of crop production. |
Yield advantages have been reported in no-till systems (relative to conventional tillage) in southern areas of the United States. Less consistent results have been reported in the northern US (due to colder/wetter springs and and poorly drained soils). |
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Use of controlled drainage structures may help retain water to facilitate off-season soil moisture recharge and could possibly raise the water table to help alleviate short-term water deficit conditions. |
Cost of installation is high, and the benefit may not be realized every year. Its suitability will be location specific. |
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Installation of irrigation systems – a common strategy in western US Midwest (e.g., Kansas, Nebraska). |
Many of the limitations would be the same as the use of controlled drainage structures (high costs and inconsistent benefits for our region). |
References
- Corn Response to Long-Term Weather Stressors
ANR-0150: https://ohioline.osu.edu/factsheet/anr-0150
- Ortez, O. A., Lindsey, A. J., Thomison, P. R., Coulter, J. A, Singh, M. P., Carrijo, D. R., Quinn, D. J., Licht, M. A., & Bastos, L. (2023). Corn response to long-term seasonal weather stressors: A review. Crop Science, 63(6), 3210–3235. doi.org/10.1002/csc2.21101