Drought stress status of corn in Kansas
Why “pollination time” is important for corn? The success or failure of pollination will determine the number of fertile ovules that will develop into actual kernels. However, even if an ovule was fertilized that doesn’t guarantee it will develop into a kernel of grain by the end of the season. Two weeks after pollination, abortion of the fertilized ovules can take place within the corn ears. Thus, the final kernel abortion rate during that period will ultimately determine the actual kernel number to be attained at maturity. The kernel abortion rate is highly influenced by any biotic or abiotic stresses (e.g. pest pressures, hot temperatures, drought, insufficient N supply, etc.). As the stress intensifies, the abortion rate increases.
When will you be able to know if the crop’s grain yield potential has been severely or partially affected by the drought stress? Go ahead now and start looking at the corn plants and quantifying the area affected by stress. Count the number of plants per acre by taking a sample from a small area and, check the status of the plants at different parts of the day. Are those plants showing drought stress symptoms very early in the morning (i.e. leaf rolling at 9 a.m.)? Is plant height and leaf mass being severely affected by the combination of the insufficient water supply and warm temperatures?
Is the pollen being shed when silks are not yet out from the husks? Those are just “pre-mortem” observations to make, with the idea of forecasting the potential yield expected at the end of the season.
For sure, if no ear is formed (“barren plants”) within a couple of days after the flowering time, the decision is pretty straightforward. If an ear does form but drought or heat stress is severe, the decision is more difficult and depends on getting an early but reasonably accurate estimate of grain yield potential.
A very close idea of the final yield can be determined at around 30 days after silking -- even before if hot and dry conditions are severe -- just at or after the milk stage. Basically, if we can get an estimate of the number of ears per row or per unit area and some idea about the final number of grains per each unit of ear, we can forecast with a degree of uncertainty the final yield, assuming a constant seed weight, which is defined at the end of the season.
The calculation is a very simple. Start by counting the total number of kernels per ear. Consider only kernels that have similar sizes. Do not count the small kernels near the tip of the ear. Multiply that number by 0.233 (assuming a plant density of 21,000 plants per acre with a single ear per plant, and an average seed size of 70,000 kernels per bushel). For example, let’s say you sample 30 ears and the average kernel number (number of rows x total number of kernels per row) is 400 per ear. Then, 400 x 0.233 = 93 bushels/acre. Again, this is just a simple “rough” calculation you can make early in the season, and it assumes that the number of ears per acre and the seed size is constant across the entire field.
Drought stress will undoubtedly have substantial impact on potential corn yields in Kansas.
How much will yields be reduced? That question will remain unanswered for now. The answer will be area- or site-specific, as drought stress is affecting corn differently in various parts of the state.
Stay tuned and check periodically all K-State resources for more updates about this or other issues.
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