Most of the corn in Kansas is in the reproductive stages now. The latest Kansas Agricultural Statistics Service crop progress report (August 3) projected that 90% of the Kansas corn crop is at the silking stage, with 35% of the crop already at the dough stage, behind that of last year (49%). The USDA classified the corn as 49% good and 10% excellent. In several areas of the state, corn is looking above average and getting to the mid-grain filling period.
Potential vs. attainable yields in corn
Three weeks ago (July 17, 2015) a summary of the forecasted corn yields was presented in the Agronomy eUpdate for selected locations around the state (Forecasted Corn Yield Potential; Figure 1). A new round of simulations was performed by lead investigators at the University of Nebraska in collaboration with Extension educators around the Corn Belt. The change in the median yield potential (Yp) since the last forecast is presented in Table 1 as a way to understand the impact the weather has had on projected corn yields during the last three weeks. Simulated current corn growth stages are also presented in Table 1. All evaluated sites are in the reproductive stage, from blister (R2 stage; 10-14 days after flowering, grain moisture 85%) to dough (R4 stage; 24-28 days after flowering, grain moisture 70%) stages.
As the crop matures, the yield range observed between the low end and high end in Table 1 will converge toward the median yield value.
Figure 1. Locations utilized for simulation purposes for Kansas.
The corn simulation model Hybrid-Maize Model (http://hybridmaize.unl.edu) presents reliable estimations under well-managed conditions, with optimum planting time and good stand uniformity, and without the influence of biotic or abiotic stresses (e.g., hail, flooding, diseases, weeds, and insects). Under stress conditions, we can expect that the model will overestimate yields. Under severe stress conditions such as heat and drought during the early reproductive period, a good deal of kernel abortion is expected. The model does not take into account the effect of these kind of stress conditions on reproductive structures such as the kernels.
The impact of current weather conditions was reflected in the simulation performed on July 29. Simulations performed during the past week in all six locations around the state (Garden City, Hutchinson, Silver Lake, Manhattan, Scandia, and St. Joseph, Mo.) for both dryland and irrigated environments show mostly only minor or no changes in yield potential compared to the results from the model simulations performed on July 20. All sites are near or above the mean relative to long-term yield potential. Again, the model does not account for a direct impact of stress conditions on the kernel abortion process and final grain number. The estimated impact on yield can be even higher if conditions become severe enough to impact the final grain number component.
Still, as emphasized in the first round of the corn forecasted yields, 2015 potential corn yields are promising regardless of the weather conditions experienced from now until harvest.
Table 1. 2015 In-season Yield Potential Forecasts for Kansas (July 29)
Conclusions
Yield forecasts from 6 locations across Kansas (also including St. Joseph, Mo.) indicate above-average corn yield potential for the current season as compared with the long-term average. Yield forecasts can go up if favorable conditions occur throughout August. Stress conditions impacting corn in the next coming weeks will be likely to reduce yields via an impact on the final kernel weight. However, these conditions on corn yield will have less effect on yields as the crop progresses into later reproductive stages. From now on is a perfect time to perform yield estimations following the method presented in our previous Agronomy eUpdate article on July 31:
https://webapp.agron.ksu.edu/agr_social/eu_article.throck?article_id=644
You can read the full paper related to forecasted yields across the Corn Belt at:
http://cropwatch.unl.edu/hybrid-maize-july-29-yield-forecast
Ignacio Ciampitti, Cropping Systems and Crop Production Specialist
ciampitti@ksu.edu
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