July 30, 2015

Corn is or has recently finished pollinating throughout Nebraska and the Corn Belt. During the last two weeks, after the July 15 end-of-season corn yield estimates, weather conditions remained close to the long-term means in many locations. To evaluate changes in the 2015 end-of-season corn yield potential, additional simulation were performed on July 29 for the same 45 locations using the UNL Hybrid-Maize model in collaboration with faculty and extension educators from 10 universities  Details about Hybrid-Maize and the underpinning methodology to forecast end-of-season yields, as well as on interpretation and uses of yield forecasts, can be found in a previous CropWatch article.

Briefly, the Hybrid-Maize model simulates daily corn growth and development and final grain yield under irrigated and dryland conditions. The model estimates "yield potential," which is the yield obtained when the crop is not limited by nutrient deficiencies, diseases, insect pressure, or weed competition — conditions that represent an "optimal management" scenario. It also assumes a uniform plant stand at the specified plant population and no problems from flooding or hail. Because weather, soil, and management factors are "location-specific," Hybrid-Maize simulations are based on actual weather data, soil, and typical management practices at the location being simulated, based on information provided by university agronomists, extension educators, and DuPont Pioneer agronomists in each state. (See Tables 1-2.)

Irrigated and dryland yield forecasts as of July 29 are shown in Tables 3-5. The range of forecasted irrigated yields has narrowed in most locations, and probabilities of near- or above-average irrigated yields tend to consolidate at all simulated locations in Nebraska except Alliance. This is related to daytime temperatures staying close to long-term averages during the last two weeks. Similar trends appear for irrigated sites in South Dakota, Missouri and Kansas, with a reduction in the probabilities of below-average yields from July 15 estimates. In Wisconsin, however, yield trends are not clear as development has been slow and corn has not yet reached silking. In addition there is more uncertainty as to whether weather conditions will allow the crop to reach maturity. 

For dryland yields, the yield scenarios continue to be favorable. There is a high probability of near- or above-average yield (more than 80%) at 32 of the 41 dryland sites. The number of locations with a high probability of above-average dryland yields (more than 66%) has increased from eight locations (July 15) to 14 this week. However, in the western Corn Belt eight locations have probabilities equal or above 20% to having below-average yields. The probability of below-average yields is low to very low, unless unusually harsh weather conditions develop.
 

Figure 2. Summary of July 15-28 weather conditions. (Links to larger version.)

As in the previous communication, a summary of July 15-28 weather conditions (daily solar radiation, maximum and minimum temperature, total rainfall, and total [grass-based] reference evapotranspiration [ET]) are shown in Figure 2 to help readers interpret the simulated yields and changes in estimations. In Figure 2, vertical bars indicate the range for these variables based on 20+ years of weather records. The horizontal thick line indicates the long-term average while the red dots indicate the 2015 averages. At most sites, rainfall has been near normal during the last two weeks (July 15-28). It has been below normal in some locations in the eastern Corn Belt (Illinois and Indiana); however, water demand during this period was likely satisfied by accumulated water in the soil profile from abundant rainfall the previous month (Figure 3).

Daytime temperatures have been close to normal throughout the Corn Belt, with nighttime temperatures remaining near normal or slightly above normal (Kansas and Missouri). In addition, reference ET has remained close to or slightly below normal throughout the region. As the season progresses and observed weather data become available, the range of forecasted yields has narrowed, in this case toward near- and above-average yields in relation to close to normal weather conditions. 

Conclusions

The probability of below-average irrigated yields in Nebraska is above 20% only in Alliance. In most of the irrigated locations across the Corn Belt, yield forecasts have a high probability of being close to or above long-term average yields. These forecasts do not take into consideration problems with stand emergence due to residue, hail/flooding damage, replanting situations, disease/insect issues, or nutrient deficiencies. Therefore, in fields negatively affected by these constraints, actual yields will be lower than the estimates provided here. We will follow-up with an updated forecast in mid-August including an estimate of the range of dates for the black-layer stage and estimation for the probability of early-killing frost in each location.

Francisco Morell, UNL Post-doctoral Research Associate
Patricio Grassini, UNL Assistant Professor of Agronomy and Horticulture, Extension Cropping System Specialist and Water for Food Institute Fellow
Haishun Yang, UNL Associate Professor of Agronomy and Horticulture and Water for Food Institute Fellow
Kenneth Cassman, UNL Professor of Agronomy and Horticulture and Robert B. Daugherty Water for Food Institute Fellow
Roger Elmore, UNL Professor of Agronomy and Horticulture, Extension Cropping System Specialist and Water for Food Institute Fellow
Justin Van Wart, UNL Post-doctoral Research Associate
Keith Glewen, Nebraska Extension Educator
Jennifer Rees, Nebraska Extension Educator
Greg Kruger, UNL Assistant Professor of Agronomy and Horticulture and UNL Extension Cropping System Specialist
Charles Shapiro, UNL Extension Soils Scientist – Crop Nutrition and Professor of Agronomy and Horticulture
Ignacio Ciampitti, Crop Production and Cropping System Specialist and Assistant Professor of Agronomy, Kansas State University
Mark Licht, Extension Cropping System Agronomist, Iowa State University
Peter Thomison, Extension Specialist and Professor, Ohio State University
Joe Lauer, Professor, University of Wisconsin-Madison
Sylvie Brouder and Tony Vyn, Professors of Agronomy, Purdue University
Ray Massey, Extension Professor, University of Missouri
Cameron Pittelkow, Assistant Professor, University of Illinois
Chris Graham, Assistant Professor, South Dakota State University
Jeff Coulter, Associate Professor and Extension Specialist, University of Minnesota