Most of the corn in Kansas is at the reproductive stages now. The latest Kansas Agricultural Statistics Service crop progress report (August 3) projected that almost 94% of the Kansas’ corn crop is at the silking stage, with more than 50% of the crop already at the dough stage, well ahead of last year (38%). The USDA classified the corn as 43% good and 14% excellent, similar to the previous week. In areas that have not received rain recently, corn is showing an anticipated and rapid senescence, moving from the bottom part of the plant to the upper leaves.
Potential vs. attainable yields in corn
Two weeks ago a summary of the forecasted corn yields was presented in the Agronomy eUpdate for the selected locations around the state of Kansas (http://ksu.ag/1tKVL9c ; Figure 1). A new round of simulations was performed by lead investigators at the University of Nebraska (Professors Patricio Grassini, Roger Elmore, Haishun Yang, and Ken Cassman) 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 (last column on the right) as a way to understand the impact the weather has had on projected corn yields during the last two weeks. As the crop matures, the yield range observed between 25% (accounting for above-normal growing conditions from now until harvest) and 75% (accounting for below-normal conditions) will converge towards 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, 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 as compared with the final observed yields on these locations. Likewise, under severe stress conditions such as heat and drought during the early reproductive period, a large kernel abortion is expected. The model does not take into account the effect of the stress conditions on the reproductive structures such as the kernels. Therefore, the model will overestimate the final yield for environments with mild to severe stress that impacts the final grain number.
Impact of the current weather was reflected in the simulation performed on August 1. Further details related to the model employed for performing these simulations can be found at: http://cropwatch.unl.edu/archive/-/asset_publisher/VHeSpfv0Agju/content/2014-forecasted-corn-yields-based-on-hybrid-maize-model-simulations-as-of-july-20th
Simulations performed during the last week in all five locations around the state (Garden City, Hutchinson, Silver Lake, Manhattan, and Scandia) 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. An exception to this rule is the Manhattan location, which has a reduction in projected yields of 9% under a dryland environment. A similar reduction in yield since the July 20 projections can be extrapolated for most dryland corn in east central Kansas. 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 were severe enough to impact the final grain number component.
For most of the locations simulated in Kansas the 2014 median yield potential forecasted as of August 1 is 10% above the long-term yield potential -- except for Manhattan dryland and Garden City under irrigation. In Manhattan and Garden City, if the conditions until harvesting worsen (represented by the 75% column in Table 1), the final yield for current season can be predicted to be similar to the long-term average yields. Favorable grain-filling environments will promote higher-than-average corn yields at all locations (the 25% column in Table 1).
As it was emphasized in the first round of the corn forecasted yields, 2014 potential corn yields are promising regardless of the weather conditions experienced from now until harvest.
Table 1. 2014 In-season Yield Potential Forecasts for Kansas (August 1).
Yield forecasts from 5 locations across Kansas indicate above-average corn yield potential for the current season as compared with the long-term average. For central and east central Kansas, dry conditions can increase the discrepancy between the observed (on-farm) and forecasted (predicted by the model) yields. Irrigated corn yield potential looks to be above the average, especially for the Scandia and Silver Lake areas. 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 be less effect on yields as the crop progresses into later reproductive stages. From now on, there is a perfect time to go out and start to perform yield estimation following the method presented in our previous Agronomy eUpdate article on August 1, http://ksu.ag/XpLTak
You can read the full paper related to forecasted yields in 25 locations around the Corn Belt at:
- Ignacio Ciampitti, Cropping Systems and Crop Production Specialist