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 2023 real-time crop stage were performed for 40 locations across the U.S. Corn Belt using the UNL Hybrid-Maize crop model; the data can be seen in Table 1. 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.

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 Aug. 22 and Sept. 12, 2023. Vertical bars indicate the range for these variables based on 20-plus years of weather records. The horizontal thick line indicates the long-term average and the red dots indicate the 2023 values.

Table 1. Data from simulations of 2023 end-of-season corn yield potential and real-time crop stage performed on Sept. 13.

	Location	Water regime	Long-term average yield (bu/ac) §	Range of Yp forecasts as of Sept. 13 (bu/ac)¶ 25th	Range of Yp forecasts as of Sept. 13 (bu/ac)¶ 75th	Probability (%) of 2022 yield to be: Below (relative to the long-term Yp)†	Probability (%) of 2023 yield to be: Near (relative to the long-term Yp)†	Probability (%) of 2023 yield to be: Above (relative to the long-term Yp)†	Simulated current crop stage*
NE	Alliance	Irrigated	193	196	209	6%	79%	15%	R5, Dent
	Beatrice	Dryland	160	Black layer on Aug. 28. Final yield: 187 bu/ac					Matured
		Irrigated	229	Black layer on Aug. 29. Final yield: 212 bu/ac					Matured
	Clay Center	Dryland	155	Black layer on Sept. 2. Final yield: 100 bu/ac					Matured
		Irrigated	245	Black layer on Sept. 5. Final yield: 217 bu/ac					Matured
	Concord	Dryland	173	Black layer on Aug. 31. Final yield: 122 bu/ac					Matured
		Irrigated	248	Black layer on Sept. 8. Final yield: 229 bu/ac					Matured
	Elgin	Irrigated	252	Black layer on Sept. 6. Final yield: 225 bu/ac					Matured
	Holdrege	Dryland	112	Black layer on Sept. 1. Final yield: 116 bu/ac					Matured
		Irrigated	242	233	236	0%	100%	0%	R5, Dent
	McCook	Dryland	86	Black layer on Aug. 27. Final yield: 99 bu/ac					Matured
		Irrigated	224	Black layer on Aug. 31. Final yield: 201 bu/ac					Matured
	Mead	Dryland	181	Black layer on Sept. 2. Final yield: 196 bu/ac					Matured
		Irrigated	234	Black layer on Sept. 1. Final yield: 221 bu/ac					Matured
	North Platte	Dryland	90	Black layer on Sept. 6. Final yield: 113 bu/ac					Matured
		Irrigated	234	213	220	2%	98%	0%	R5, Dent
	O'Neill	Irrigated	226	221	226	0%	100%	0%	R5, Dent
IA	Ames	Dryland	228	Black layer on Sept. 3. Final yield: 206 bu/ac					Matured
	Crawfordsville	Dryland	227	Black layer on Sept. 1. Final yield: 154 bu/ac					Matured
	Lewis	Dryland	205	Black layer on Aug. 31. Final yield: 214 bu/ac					Matured
	Nashua	Dryland	228	Black layer on Sept. 2. Final yield: 153 bu/ac					Matured
	Sutherland	Dryland	208	Black layer on Sept. 6. Final yield: 171 bu/ac					Matured
IL	Bondville	Dryland	235	235	238	0%	100%	0%	R5, Dent
	Freeport	Dryland	213	Black layer on Sept. 6. Final yield: 184 bu/ac					Matured
	Olney	Dryland	191	Black layer on Aug. 26. Final yield: 202 bu/ac					Matured
	Peoria	Dryland	211	Black layer on Sept. 9. Final yield: 242 bu/ac					Matured
	Springfield	Dryland	182	Black layer on Aug. 29. Final yield: 220 bu/ac					Matured
IN	Butlerville	Dryland	224	221	221	0%	100%	0%	R5, Dent
	Columbia City	Dryland	224	250	274	0%	15%	85%	R5, Dent
	Davis	Dryland	230	239	256	0%	65%	35%	R5, Dent
	West Lafayette	Dryland	236	236	243	0%	100%	0%	R5, Dent
KS	Garden City	Irrigated	217	Black layer on Aug. 31. Final yield: 193 bu/ac					Matured
	Hutchinson	Dryland	99	Black layer on Aug. 10. Final yield: 97 bu/ac					Matured
	Manhattan	Dryland	137	Black layer on Aug. 16. Final yield: 160 bu/ac					Matured
	Scandia	Dryland	129	Black layer on Aug. 21. Final yield: 95 bu/ac					Matured
		Irrigated	226	Black layer on Aug. 24. Final yield: 190 bu/ac					Matured
	Silverlake	Dryland	141	Black layer on Aug. 18. Final yield: 164 bu/ac					Matured
		Irrigated	209	Black layer on Aug. 22. Final yield: 210 bu/ac					Matured
MI	Ceresco	Dryland	180	180	208	0%	45%	55%	R4, Dough
MN	Eldred	Dryland	114	Black layer on Sept. 6. Final yield: 83 bu/ac					Matured
	Lamberton	Dryland	212	Black layer on Sept. 1. Final yield: 169 bu/ac					Matured
	Waseca	Dryland	219	Black layer on Sept. 4. Final yield: 176 bu/ac					Matured
MO	Brunswick	Dryland	181	Black layer on Aug. 27. Final yield: 93 bu/ac					Matured
	Monroe City	Dryland	175	Black layer on Aug. 27. Final yield: 131 bu/ac					Matured
	St. Joseph	Dryland	169	Black layer on Aug. 24. Final yield: 199 bu/ac					Matured
ND	Dazey	Dryland	108	94	97	79%	21%	0%	R5, Dent
OH	Custar	Dryland	208	229	255	0%	21%	79%	R5, Dent
	South Charleston	Dryland	216	235	248	0%	45%	55%	R5, Dent
	Wooster	Dryland	210	197	231	8%	66%	26%	R4, Dough

§Long-term (last 20-plus years) potential yield at each location and surrounding area.
¶ Range of forecasted 2023 potential yields based on average planting date in 2023, indicating the potential yields in the 25th and 75th percentile of the potential yield distribution (associated with respective adverse and favorable weather scenarios during the rest of the season).
† Probability of obtaining a 2023 yield below (10%) than the long-term potential yield at each location.

Crop Stages and Weather Conditions During the Last Three Weeks

Corn has reached black layer stage at most of the sites, except for those located in western and eastern fringes of the region, including ND, western NE, IN and OH (Figure 2). During the late grain filling, temperature was above normal and rainfall below normal, except for the eastern region where temperature and rainfall were near average (IN and OH). Indeed, several sites across IN, IL, IA, MN and KS received very little or no rainfall during this period.

A summary of weather conditions during the past three weeks is shown in Figure 1.

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).

Near but Below Average Yields in Irrigated Corn

Forecasted end-of-season irrigated yields are shown in Figure 3 and 4. About two thirds of the irrigated sites (eight out of 13) exhibited near-average yields. Compared with our previous forecast, forecasted yields are 7% lower because of higher temperatures during the last half of the grain filling. Although most irrigated sites present forecasted yields near historical records, expected yields are consistently lower than historical averages (average: 8% lower) and similar to the previous (2022) season.

Rainfed Corn: Yield Potential is Highly Variable Across Rainfed Sites

Lack of rainfall and high temperatures during the last portion of the seed filling led to a reduction of the projected end-of-season rainfed yields by nearly 5% compared to our previous forecast. Still, one-third (10 out of 36) of the sites are expected to achieve above-average yields. These sites are scattered across the region, including portions of western NE, northeast KS, southeastern NE, northwestern MO, IL, IN and OH (Figures 3 and 4).

Conversely, another third of the sites (13 out of 36) exhibit below-average yields. These sites are situated in the central and western areas of the Corn Belt (eastern IA, northwestern IL, northern MO, northeastern and south-central NE, north-central KS) and the northwestern region (north of IA, MN and ND).

The remaining sites showed a high probability of near-average yield and are located in the eastern part of the Corn Belt (eastern IL, IN and OH, and southern IA).

Overall, the 2023 yield scenario appears to be slightly more favorable than the previous year (2022) but is still 6% below the long-term average. Compared to the 2022 season, forecasted yield is higher for the current 2023 season for rainfed sites in NE, southwestern IA and southern KS. Conversely, 15% or more lower yield is forecasted for southern MN, northeastern IA, and MO compared with the previous year.

Figure 3. Vertical lines indicate the range of forecasted 2023 corn yield potential by Sept. 13 based on average 2023 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 average yield potential at each location and the red dots represent the forecasted 2023 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 2023 yield potential to be below (10%, green color) the long-term 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

Aggregated at regional level, our forecasted yield potential this season is 7% below the historical average for both rainfed and irrigated corn. In line with USDA predictions, our forecast reduced expected yields compared to the August report and foresees similar average yield compared to that from last year.

Our forecast suggests a near average year for a majority of irrigated sites although 40% of them can expect yields to be below the historical average.

For rainfed corn, the scenario is diverse across regions. Most sites in the eastern part of the Corn Belt and a few scattered sites in central and western areas have a high probability of near-average rainfed yields. Above-average yield is expected at 10 locations scattered across the west and eastern areas of the Corn Belt. Conversely, 13 sites located in central, western and northwestern fringes of the Corn Belt exhibit a high probability of below-average rainfed yields.

Note that these forecasts do not take into consideration problems with stand emergence, hail/flooding 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.