July 19, 2012

Nebraska Rainfed Corn 22-42 bu/ac Below Average; Irrigated Corn 2-9 bu/ac Below Average

Continued hot dry conditions are hitting dryland corn fields across the Corn Belt, with only some seeing relief from precipitation.

Figure 1. Locations used by the Hybrid-Maize model for in-season yield forecasting with actual weather and dominant management practices and soil series at each site (indicated by starts).  Green areas indicate where corn is planted.  Weather data used is from the High Plains Regional Climate Center and the Water and Atmospheric Resources Monitoring Program through the Illinois Climate Network (Illinois State Water Survey, Prairie Research Institute, and the University of Illinois at Urbana-Champaign).  (See larger version of Figure 1 and Table 1)

Predictions of 2012 end-of-season yield were performed July 15 using the Hybrid-Maize model to evaluate, in “real-time,” the impact of current weather on corn yield potential and its geospatial variability across the Corn Belt. Simulations were run for dryland corn in Iowa, Illinois, and South Dakota and for irrigated and dryland corn in Nebraska (Figure 1). Simulations are based on actual planting dates, hybrid relative maturity, plant population, weather, and soil properties at each location.

Modeling Yield

Details about Hybrid-Maize and the underpinning methodology used to forecast end-of-season yields can be found in a previous CropWatch article (Forecasted Corn Yields Based on Hybrid-Maize Model). Briefly, Hybrid-Maize is a corn simulation model that estimates corn yield potential under irrigated or dryland conditions, based on weather and soil type, assuming optimal crop management. To predict end-of-season yields, Hybrid-Maize uses actual weather data up to the date of the yield forecast (in this case, July 15) and historical, long-term weather data (over 20 years) to simulate a range of potential yields by the end of the crop season. By comparing this range of simulated end-of-season yields against the long-term average simulated yield, we can estimate the likelihood of below-, near-, or above-average yields and the magnitude of difference from average yields.

End-of-Season Yield Potentials as of July 15

Corn Yield Potential (Yp) forecasts, as well as the underpinning data used for the simulations, can be seen in Table 1. The long-term yield potential prediction based on 30 years of weather data (Table 1, fourth column from the right) is compared to the range of predicted 2012 corn yield potential (three columns on the right), which includes the yield potential simulated under the most likely scenario of weather expected for the rest of the season (median) and for relatively favorable and unfavorable scenarios for the rest of the season (75th and 25th percentiles) based on historical weather data.

According to the July 15 simulations, the “most likely” end-of-season dryland corn yield potential in Nebraska, Iowa, and southeastern Illinois (“median” yields, red column in Table 1) is 10% to 26% below the long-term average yield potential (Table 1). Even if weather turns favorable for dryland corn during the rest of the 2012 season, the resulting yields (75th yields, blue column in Table 1) are still likely to be below the long-term average (Table 1). How about if dry and hot conditions persist? Certainly the likehood and magnitude of yield reduction in dryland corn will increase. In fact, Hybrid-Maize predicts dryland corn yield potential to be about 30% to 40% below the long-term average if weather remains hot and dry for the rest of the season (25th yields, green column in Table 1). The only bright spots in this analysis were in Illinois at DeKalb and Monmouth where rainfall during the past two weeks appears to have provided relief. At these sites, current projects indicate that end-of-season yields will be near their long-term averages unless weather once again turns dry and hot at those locations (Table 1). Likewise, recent weather conditions at Brookings, S.D. have been conducive to achieve yields near the long-term average.

What about irrigated corn in Nebraska? Contrary to the projections for dryland corn, irrigated corn yield potential is only two to three bushels below the long-term average at Holdrege, Mead, and Concord (Table 1). High nighttime temperatures during the last two weeks at Clay Center have hastened crop development and increased nighttime respiration costs, leading to a projected yield potential that is 9 bushels below the long-term average. At O’Neill last week’s weather did not depart from historical temperature norms, hence, projected yield potential is still near-average. But it is important to keep in mind that if hot weather persists for the rest of the season, the likehood (and magnitude) of below-average yields will increase for irrigated corn due to more rapid maturation and a shorter grain-filling period.

Summary

Projected 2012 end-of-season yields are well below the long-term yield average for dryland corn in Nebraska, Iowa, and southeastern Illinois and near average in South Dakota and central-west Illinois. Projected yield for irrigated corn in Nebraska is slightly below average at most locations, except for Clay Center, which it’s 9 bushels below average and O’Neill where it’s near average. If hot, dry conditions persist during coming weeks, we expect projected yields will drop substantially under both dryland and irrigated conditions. We will continue to update these projections as the season progresses.

Patricio Grassini, Research Associate Professor, Department of Agronomy and Horticulture
Jenny Rees, UNL Extension Educator
Haishun Yang, Professor, Department of Agronomy and Horticulture
Kenneth G Cassman, Professor, Department of Agronomy and Horticulture