Simulations of 2023 end-of-season corn yield potential and real-time crop stage were performed on Aug. 2 for 40 locations across the U.S. Corn Belt using the UNL Hybrid-Maize crop model in collaboration with faculty and extension educators from 10 universities. This article summarizes the simulated crop stages and yield forecasts; 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, as well as on interpretation and uses of yield forecasts, are described in a previous article.

A summary of weather conditions during the last three weeks is shown in Figure 1. Over the past three weeks, average air temperature has remained near average values in most of the Corn Belt. However, sites located in ND, MN, and most of IA showed night temperatures below historical average while two sites in MO have experienced above-average day-time temperatures. Rainfall was well below normal in MO, MN, ND, northern and eastern IA, and some spots in OH, IL and NE. Rainfall was near normal records in the remaining locations.

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 July 11 and Aug. 1, 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 for the same period. Table 1. Data from simulations of 2023 end-of-season corn yield potential and real-time crop stage performed on Aug. 2.

	Location	Water regime	Long-term average yield (bu/ac) §	Range of Yp forecasts as of Aug 02 (bu/ac)¶ 25th	Range of Yp forecasts as of Aug 02 (bu/ac)¶ 75th	Probability (%) of 2023 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	185	221	15%	47%	38%	R1, Silking
	Beatrice	Dryland	160	179	195	0%	21%	79%	R4, Dough
		Irrigated	229	207	223	24%	76%	0%	R3, Milk
	Clay Center	Dryland	155	105	173	66%	2%	32%	R3, Milk
		Irrigated	245	218	242	27%	73%	0%	R3, Milk
	Concord	Dryland	173	143	214	39%	22%	39%	R3, Milk
		Irrigated	248	236	263	10%	78%	12%	R3, Milk
	Elgin	Irrigated	252	226	257	31%	60%	9%	R3, Milk
	Holdrege	Dryland	112	80	132	49%	17%	34%	R3, Milk
		Irrigated	242	217	253	26%	63%	11%	R2, Blister
	McCook	Dryland	86	76	195	29%	27%	44%	R3, Milk
		Irrigated	224	198	228	29%	68%	2%	R3, Milk
	Mead	Dryland	181	169	206	17%	44%	39%	R3, Milk
		Irrigated	234	215	237	15%	76%	10%	R3, Milk
	North Platte	Dryland	90	113	137	0%	5%	95%	R2, Blister
		Irrigated	234	221	263	17%	51%	32%	R2, Blister
	O'Neill	Irrigated	226	221	260	8%	55%	37%	R2, Blister
IA	Ames	Dryland	228	204	231	29%	63%	9%	R3, Milk
	Crawfordsville	Dryland	227	152	180	91%	9%	0%	R3, Milk
	Lewis	Dryland	205	187	216	20%	68%	12%	R4, Dough
	Nashua	Dryland	228	175	193	94%	6%	0%	R2, Blister
	Sutherland	Dryland	208	172	207	41%	47%	12%	R3, Milk
IL	Bondville	Dryland	235	210	243	26%	61%	13%	R3, Milk
	Freeport	Dryland	213	215	240	6%	64%	30%	R3, Milk
	Olney	Dryland	191	191	210	9%	58%	33%	R4, Dough
	Peoria	Dryland	211	200	232	3%	70%	27%	R3, Milk
	Springfield	Dryland	182	159	195	30%	48%	22%	R3, Milk
IN	Butlerville	Dryland	224	214	227	5%	90%	5%	R2, Blister
	Columbia City	Dryland	224	235	255	0%	50%	50%	R2, Blister
	Davis	Dryland	230	232	259	0%	55%	45%	R2, Blister
	West Lafayette	Dryland	236	220	224	25%	70%	5%	R2, Blister
KS	Garden City	Irrigated	217	196	220	24%	70%	5%	R3, Milk
	Hutchinson	Dryland	99	87	103	45%	39%	15%	R5, Dent
	Manhattan	Dryland	137	133	162	13%	37%	50%	R4, Dough
	Scandia	Dryland	129	54	87	100%	0%	0%	R4, Dough
		Irrigated	226	201	220	27%	73%	0%	R4, Dough
	Silverlake	Dryland	141	146	170	0%	41%	59%	R4, Dough
		Irrigated	209	199	221	8%	81%	11%	R4, Dough
MI	Ceresco	Dryland	180	199	230	0%	23%	77%	V16
MN	Eldred	Dryland	114	39	75	89%	11%	0%	R2, Blister
	Lamberton	Dryland	212	179	206	46%	46%	8%	R3, Milk
	Waseca	Dryland	219	190	221	44%	53%	2%	R3, Milk
MO	Brunswick	Dryland	181	75	88	100%	0%	0%	R4, Dough
	Monroe City	Dryland	175	83	109	100%	0%	0%	R4, Dough
	St. Joseph	Dryland	169	164	188	13%	57%	30%	R4, Dough
ND	Dazey	Dryland	108	84	134	29%	29%	43%	R2, Blister
OH	Custar	Dryland	208	212	239	3%	45%	53%	R1, Silking
	South Charleston	Dryland	216	185	235	36%	45%	18%	R2, Blister
	Wooster	Dryland	210	193	225	18%	61%	21%	V16

§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.

Simulated Corn Stage Across 40 Locations

Corn has reached the kernel milk stage, except for the northern and eastern fringes of the region. Corn in the southern fringe (KS, MO and southern IL) is ahead of the rest of the locations, having already reached the dough and even the dent stage (Figure 2). The current corn stage is similar to that reported by early August last year, except at ND, MO and southern IA, where crop development has been faster.

Figure 2. Simulated developmental stage for irrigated and rainfed corn at each location. Vn: vegetative stage (nth leaf); R1: silking; R2: blister; R3: milk; R4: dough; R5: dent. 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. Six out of 13 sites in eastern NE and KS exhibit a high probability (>75%, that is, a chance of three out of four) of near-average yield potential. Near-average yield is also likely in the rest of the sites, depending upon the temperature during the rest of August. At this point, the forecasted scenario for irrigated maize in the current season seems better than 2022.

Variable 2023 Forecasted Corn Yield Across Rainfed Locations

Forecasted yield potential is highly variable across the 35 rainfed sites (Figures 3 and 4). Two regions have a high probability of below-average yields: one includes portions of MN and MO and eastern IA, and other includes south-central NE and north-central KS. Conversely, there is a high probability of above-average or near-average yield (>75%) in western IA, the eastern fringe of the region and a few spots in NE.

Compared with our previous forecast, below-average rainfall in eastern IA and most of northern MO during the past three weeks increased the probability of below-average yields in that area, reducing the forecasted yield for the 2023 season. A few scattered sites in the eastern states (IL, IN and OH) have reduced the probability of above-average yields due to below-average rainfall and above-average daytime temperatures in the last three weeks. In contrast, due to cooler weather in southeastern NE, the associated yield forecasts have been improved relative to mid-July, now showing a high probability of near- and even above-average yields.

Compared with the 2022 forecast, the forecasted scenario for rainfed maize seems more favorable in NE (except for south-central sites) and western IA, while in MO, eastern IA and MN, and western IL the scenario looks more pessimistic. In the remaining area, the scenario looks similar to the 2022 season.

Figure 3. Vertical lines indicate the range of forecasted 2023 corn yield potential by Aug. 2 based on average planting date in 2023 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 (2005-2022) average yield potential at each location. 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 (2005-2022) 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

There is a high probability of near-average yields for most of the irrigated sites, while for rainfed corn the scenario is diverse across regions. Most sites in the eastern part of the Corn Belt have a high probability of near-average yields, while above-average yield is expected at MI and a few spots in NE. In contrast, two regions, one in south-central NE and north-central KS, and the other in MO, eastern and northern IA, and MN exhibit a high probability of below-average yields. Temperature and rainfall during August will define the trend for all sites across the region.

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 the ones reported here in fields with planting dates or hybrid maturities that differ markedly from those used as the basis for the forecasts. We will follow up with further forecasts in late August.