August 2, 2012

Latest data show irrigated yields to take a hit.

Hot dry conditions have struck hard at dryland corn fields all across the Corn Belt. Predictions of 2012 end-of-season yield were performed as of July 30 using the Hybrid-Maize model to evaluate, in "real-time" fashion, 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 both irrigated and dryland corn in Nebraska (Figure 1). Simulations are based on actual planting dates, hybrid relative maturity, plant population, and weather and soil properties at each location. Details about using the Hybrid-Maize model and the underpinning methodology to forecast end-of-season yields can be found in a previous CropWatch article and are summarized briefly in the box.

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). Link to larger versions of Figure 1 and Table 1. How Hybrid-Maize Forecasts Yield Potential 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 30) and historical, long-term (20+ years) weather data to simulate a range of possible potential yields by the end of the crop season. By comparing this range of possible simulated end-of-season yields, against the long-term average simulated yield, it is possible to estimate the likehood for below, near, or above-average yields and also the magnitude of the difference above or below. 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 (fourth column from the right) is compared to the range of predicted 2012 corn yield potential (three columns on the right. These include 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. There is a 50% probability that end-of-season yield potential will fall within the 25th to 75th percentile range. Likewise, the yield percentiles indicate that end-of-season yield potential is expected to be lower than the 75th percentile and 25th percentile yields in 75% (3 out of 4) and 25% (1 out of 4) of the possible rest-of-season weather scenarios, respectively. Earlier 2012 Forecasts in CropWatch 2012 Potential Corn Yields Based on July 15 Hybrid-Maize Model Simlations Forecasted Corn Yields Based on July 1 Hybrid-Maize Model Simulations

Dryland Yields

Based on the July 30 Hybrid-Maize Model simulations, for dryland corn, the most likely end-of-season yield potential in Nebraska, Iowa, and southeastern Illinois ("median" in Table 1) is 8% to 47% below the long-term average yield potential, with an average of 30% yield reduction across locations (Table 1). The fact that the 75th percentile yield is well below the long-term average at all locations indicates a very high probability (near 100%) of below-average dryland yields, except for Brookings, S.D. where there is still a slightly higher probability (1 out 4) of achieving near-average dryland yield (Table 1).

Compared with the July 15 prediction, the expected end-of-season dryland corn yield potential in South Dakota and Illinois has dropped substantially due to insufficient rains during the last two weeks. If hot dry conditions persist, Hybrid-Maize predicts dryland corn yield potential would drop about 40% below the long-term average across the Corn Belt (25th percentile yields in Table 1).

Irrigated Yields

What about irrigated corn in Nebraska? Median end-of-season irrigated corn yield potential is 5-8% below the long-term average at Holdrege, Clay Center, Mead, Concord, and O'Neill (Table 1). High nighttime temperature during the last two weeks has not only hastened crop development but also increased nighttime respiration costs which led to a projected yield potential that is below the long-term average.

Comparison of the 75th percentile yield against the long-term average yield indicates that there is a 75% probability (3 out of 4) of below-average irrigated yields at all locations in Nebraska, except O'Neill. There is still a slightly higher probability of achieving near-average irrigated yield at O'Neill (Table 1). However, 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 irrigated yields will increase for irrigated corn due to more rapid maturation and thus a shorter grain-filling period, with an expected average yield reduction of 10% as indicated by the 25th percentile yield (Table 1).

In a Nutshell

To summarize,

• Projected 2012 end-of-season corn yields are, on average, 30% (dryland) and 8% (irrigated) below the long-term averages.
• There is very high probability (near 100%) of below-average dryland yields and also a high probability (3 out of 4) of below-average irrigated yields at all locations except dryland corn at Brookings, S.D. and irrigated corn at O'Neill.
• If dry hot conditions persist for the coming weeks, we expect that projected yields would drop further under both dryland and irrigated conditions.

We will continue to update these projections as the season progresses.

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