Patricio Grassini, UNL Associate Professor of Agronomy and Horticulture, Extension Cropping System Specialist and Water for Food Institute Fellow; Jose Andrade, UNL Affiliate; Juan Ignacio Rattalino Edreira, UNL Research Assistant Professor of Agronomy and Horticulture; Gonzalo Rizzo, UNL PhD student; Haishun Yang, UNL Associate Professor of Agronomy and Horticulture and Water for Food Institute Fellow; Keith Glewen & Jennifer Rees, Nebraska Extension Educators; Jeff Coulter, Professor and Extension Specialist, University of Minnesota; Mark Licht (Extension Cropping System Agronomist) & Sotirios Archontoulis (Assistant Professor), Iowa State University; Ignacio Ciampitti, Crop Production and Cropping System Specialist and Assistant Professor of Agronomy, Kansas State University; Ray Massey, Extension Professor, University of Missouri

This is the last article in a series that summarizes the simulated crop stages and yield forecasts across the Corn Belt. To evaluate, in “real-time,” the impact of this season’s weather on corn yield and its spatial variability across the Corn Belt, simulations of 2020 real-time crop stage were performed for 40 locations across the US Corn Belt using the UNL Hybrid-Maize crop model; the data can be downloaded here. Details on the UNL Hybrid-Maize crop model and the underpinning methodology to simulate phenology and forecast end-of-season yields is described in a previous article. Note that one location in IA (Kanawha) was not included due to lack of weather data.

Crop Stages and Weather Conditions During the Past Month

Corn has reached black layer at most locations of the Corn Belt, except for a few scattered sites in northern NE, IA, MN, IL, and MI (Figure 2). During the last three weeks, most locations exhibited near-normal rainfall except for a few sites in MN, IL, and OH that showed above-normal rainfall. Air temperature tended to be below normal in the western fringe of the Corn Belt (ND, NE, and KS), while in the remaining area, air temperature has remained near normal. A summary of weather conditions during the past three weeks is shown in Figure 1.

Figure 1. Daily solar radiation, maximum and minimum air temperature (Tmax and Tmin), total rainfall, and total reference grass-based evapotranspiration (ET) for the time period between August 25 and September 14, 2020. Vertical bars indicate the range for these variables based on 20+ years of weather records. The horizontal thick line indicates the long-term average and the red dots indicate the 2020 values.

Figure 2. Simulated developmental stage for irrigated and rainfed corn at each location. R5: dent; physiological maturity: matured. Separate maps are shown for irrigated corn (top) and rainfed corn (bottom).

Near Average Yields in Irrigated Corn

Forecasted end-of-season irrigated yields are shown in Figure 3 and 4. More than 90% of the irrigated sites (12 out of 13) exhibited near-average yields. Only one site presented above-average yields (Scandia, KS). Overall, the irrigated maize yield potential forecasted for the current 2020 season seems similar to that forecasted in the previous (2019) season.

Rainfed Corn: Yield Potential is Highly Variable Across Rainfed Sites but Below Last Year

Forecasted end-of-season yields for rainfed corn indicate above-average yield at one third (12 out of 36) of the sites (Figure 3 and 4) situated in KS, ND, MI, MN, northern IL, northwestern MO, and in Beatrice (NE). In contrast, most sites in the southcentral and southeastern parts of the Corn Belt, as well as one site in southcentral NE, exhibited near average yields. Finally, nine sites across NE and IA and one site in OH (Custar) showed a high probability for yield to be below average.

Figure 3. Vertical lines indicate the range of forecasted 2020 corn yield potential by September 15 based on average 2020 planting date at each location. Horizontal lines indicate the 25th and 75th percentiles of the yield distribution (associated with respective adverse and favorable weather scenarios during the rest of the season). The blue squares indicate the long-term (2005-2019) average yield potential at each location and the red dots represent the forecasted 2020 corn yield potential at sites that have already reached maturity. Separate charts are shown for irrigated corn (top) and rainfed corn (bottom).

Figure 2. Probability of the 2020 yield potential to be below (10%, green color) the long-term (2005-2019) average yield potential at each location. Separate maps are shown for irrigated corn (top) and rainfed corn (bottom). The larger a color section is within the pie chart, the higher the probability that end-of-season corn yield will be in that category.

Conclusions

In contrast to the record-yield prediction made by USDA-NASS, our forecasted yield potential this season is near to the historical average record and 15% lower compared with the 2019 crop season. Our forecasts suggest a near-average year for irrigated corn at most sites. For rainfed corn, the scenario is diverse across regions. Most sites in the southeastern part of the Corn Belt, as well as in eastern IA and MO, are expected to show near-average yields. Above-average yields are estimated at 12 locations, mostly located in the northern and southwestern fringes of the region and in northern IL. In contrast, below-average yields are expected at 10 sites located in NE and IA and also in northwestern OH.

Note that these forecasts do not take into consideration problems with stand emergence, hail/flooding/wind damage, replanting situations, disease, or nitrate leaching. In fields negatively affected by these constraints, actual yields will be lower than estimates provided here. It is important to keep in mind that yield forecasts are not field-specific and, instead, represent an estimate of average on-farm yield for a given location and surrounding area in absence of the yield-reducing factors mentioned here. Likewise, crop stages and forecasted yields will deviate from the ones reported here in fields with planting dates or hybrid maturities that differ markedly from the ones used as the basis for the forecasts.