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 article summarizes the simulated crop stages and yield forecasts performed on August 25 for 40 locations across the US Corn Belt using the UNL Hybrid-Maize crop model; the data can be downloaded here. Details on the underpinning methodology to simulate phenology and forecast end-of-season yields, as well as on interpretation and uses of yield forecasts, are described in a previous article. Note that one location in IA (Kanawha) was not included due to lack of weather data.

During the last three weeks, solar radiation was above the historical average in most of the Corn Belt. Air temperature tended to be near average across the entire region, except for KS and MO, where most sites presented below average records, and NE and IA, where daytime temperature tended to be above normal. Rainfall was well below average at most locations, except for MN with rainfall above normal and some locations in IL, IN, and OH with near-average rainfall. A summary of weather conditions during the last 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 4 and August 25, 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.

Simulated Corn Stage Across 40 Locations

Corn has reached kernel dent stage at most locations, except for a few sites in the eastern and northern fringes of the region where it is still in dough stage. Corn has reached physiological maturity (black layer stage) at most sites in KS (Figure 2).

Figure 2. Simulated developmental stage for irrigated and rainfed corn at each location. R4: dough; R5: dent; physiological maturity: matured. Separate maps are shown for irrigated corn (top) and rainfed corn (bottom).

Irrigated Corn: High Probability of Near-average Yields

The range of forecasted irrigated corn yield potential for each location, as well as the probabilities for yields above, near, or below average, are shown in Figures 3 and 4. Almost all irrigated sites (11 out of 13) exhibit a high probability (>75%, that is, 3 out of 4 chances) of near-average yield potential. Only one site (Scandia, KS) exhibits a high probability of above-average yield potential. 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

Forecasted rainfed yield potential is highly variable across rainfed sites. A high probability (>75%, that is, 3 out of 4 chances) of above average yield potential is expected in 14 sites located in the southern (KS, western MO, and southeastern NE) and northern (MN, ND, MI) fringes of the Corn Belt as well as at most sites in IL (Figures 3 and 4). Compared with our previous forecast, below-average rainfall during the past three weeks increased the probability of below-average yield potential at most of the sites in NE and IA, and northwestern OH. The forecasted yield scenario at these sites for the current season looks more pessimistic than in 2019.

Figure 3. Vertical lines indicate the range of forecasted 2020 corn yield potential by August 25 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 4. 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

Corn has already reached the dent stage in most parts of the Corn Belt and physiological maturity in the southern fringe of the region. Compared with our previous forecasts, there is still a high probability of near-average yields for the majority of the irrigated sites. For rainfed corn, the scenario is diverse across regions. Most sites in the eastern part of the Corn Belt, as well as in eastern IA and MO, have a high probability of near- or above-average yields. Above-average yield is expected at 14 locations, mostly located in the northern and southern fringes of the region and at some sites in the eastern part of the region. In contrast, the probability of below-average yield has increased at many sites in NE and IA and also in northwestern OH. 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 those reported here in fields with planting dates or hybrid maturities that differ markedly from those used as the basis for these forecasts. We will follow up with the final forecasted yield and analysis of the 2020 crop season on Sept 15.