By Mark Licht, Department of Agronomy
With corn pollination underway, and in some cases near completion, many agronomists and farmers are now beginning to think about what corn yields will be. And because of that, some are even making corn yield predictions. We know that approximately the next 60 days of grain fill can be greatly impacted by weather conditions. To help give some insights into yield levels this fall and how extensively weather can impact those yields, Iowa is collaborating with a team from the University of Nebraska and Robert B. Daugherty Water for Food Institute to use the Hybrid-Maize model to forecast potential corn yields across the Corn Belt.
The Hybrid-Maize model estimates yield based on current and historical weather parameters with the assumption that plants stands are uniform; flooding and hail did not occur; and that typical management of nutrients, insects, diseases, and weeds are not limiting. Yield estimates resulting from Hybrid-Maize become less variable as the season progresses because of less reliance on historical weather data. This helps in understanding how current season weather conditions affected corn growth up to the date of the simulation but also gives some projections of yield estimates for the remainder of the growing season.
The long-term and forecasted yield potential for six Iowa locations is presented in Table 2. The long-term yield potential is based on 25+ years of weather data. The forecasted yield potential is based on the current weather prior to July 20, 2014, and historical weather data to predict the rest of the season, which gives a range of possible end-of-season yields depending on whether the climate for the rest of season is favorable (25% scenario), near-normal (median scenario) and unfavorable (75% scenario).
For Iowa, the median forecasted yields of the six locations ranged 0% to 26% of the long-term average yield potential (Table 2). The biggest deviation from the long-term average was the Lewis location in southwest Iowa where above normal precipitation combined with cooler temperatures has benefited the crop more than other locations. In fact, the yield projections indicate a 75% probability that yields near Lewis will be 16% or more above the normal yield. Likewise, there is 75% probability at Crawfordsville that yields will be at least 3% above normal.
Interpreting this forecasted yield potential requires the understanding that the long-term yield potential may not always match up with actual production history because of limiting factors such as fertility, weeds, insects, and diseases or because of weather events such as early frost damage, hail injury, or flooding that are not accounted for by the model. An appropriate way to interpret that data is to apply the percent deviation from long-term yield potential to your own actual production history or past county yield estimates. For instance, the 2013 state corn yield was 165 bushels per acre and based on the 6-location average percent deviations there is a 50% probability the Iowa state corn yield will be between 165 and 195 bu/ac with a median estimation of 178 bu/ac.
The full version of the July 20 simulation for all Corn Belt locations forecasted can be found at; 2014 Forecasted Corn Yields Based on July 20 Hybrid Maize Model Simulations
Of course, the best determination of yield potential for your farm will be by determining (or estimating) the yield components for your fields. The most common yield calculations include; ears per acre, kernels per ear (rows per ear time kernels per row), and kernels per bushel (often as 90,000 kernels per bushels). Better estimates are achieved when conducting estimates based on 10 ears per stop and 10 stops per field with adjustments adjustment made to kernels per bushel for kernel weight and/or size.
Acknowledgements: The data presented here is part of larger yield forecasting project coordinated by Patricio Grassini, Haishun Yang, Roger Elmore and Kenneth Cassman from the Department of Agronomy and Horticulture, University of Nebraska-Lincoln and the Robert B. Dougherty Water for Food Institute.
Table 1. Locations, soil type, maturity, and planting dates used for Iowa yield forecasting with Hybrid-Maize. Plant density was set at 34,000 plants per acre for all locations.
Table 2. In-season yield potential forecasts for the 2014 growing season in Iowa. Yield predictions are made using the Hybrid-Maize model with current weather parameters prior to July 20, 2014 followed by historical weather records for the remainder of the growing season.
Mark Licht is an Extension cropping systems agronomist with responsibilities in corn and soybean management and production. He can be reached at firstname.lastname@example.org or (515) 294-0877.