Simulations of 2021 end-of-season corn yield potential and real-time crop stage were performed on July 14 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 found 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 60 days (from May 14 to July 13) is shown in Figure 1. The season started with warm conditions throughout the north and northwestern fringes of the Corn Belt, showing temperatures above normal in ND, MN, IA, MI, and northern NE and near-normal temperature in the rest of the region. Most of the northwestern region (MN, ND, IA, and eastern NE) presented below normal rainfall. Remaining sites showed near normal rainfall records, except for MO and a few scattered locations in IL and IN with rainfall above normal.

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 May 14 and July 13, 2021. 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 2021 values for the same period.

Table 1. Data from simulations of 2021 end-of-season corn yield potential and real-time crop stage performed on July 14

	Location	Water regime	Long-term average yield (bu/ac) §	Range of Yp forecasts as of Jul 14 (bu/ac)¶ 25th	Range of Yp forecasts as of Jul 14 (bu/ac)¶ 75th	Probability (%) of 2021 yield to be: Below (relative to the long-term Yp)†	Probability (%) of 2021 yield to be: Near (relative to the long-term Yp)†	Probability (%) of 2021 yield to be: Above (relative to the long-term Yp)†	Simulated current crop stage*
NE	Alliance	Irrigated	193	188	222	3%	59%	38%	V14
	Beatrice	Dryland	162	107	168	68%	13%	19%	R1, Silking
		Irrigated	230	216	247	6%	81%	13%	R1, Silking
	Clay Center	Dryland	160	64	149	72%	15%	13%	V16
		Irrigated	245	235	257	13%	72%	15%	V18
	Concord	Dryland	177	88	142	79%	10%	10%	V16
		Irrigated	249	232	265	18%	72%	10%	V18
	Elgin	Irrigated	252	229	263	15%	76%	9%	V16
	Holdrege	Dryland	115	84	131	36%	30%	33%	V16
		Irrigated	242	225	261	12%	73%	15%	V16
	McCook	Dryland	88	68	117	31%	23%	46%	V18
		Irrigated	225	211	235	18%	72%	10%	V18
	Mead	Dryland	183	118	190	59%	28%	13%	V18
		Irrigated	235	217	247	21%	64%	15%	R1, Silking
	North Platte	Dryland	91	43	99	56%	21%	23%	V14
		Irrigated	234	223	260	13%	51%	36%	V16
	O'Neill	Irrigated	227	205	239	25%	61%	14%	V16
IA	Ames	Dryland	231	176	203	82%	18%	0%	R1, Silking
	Crawfordsville	Dryland	230	224	246	10%	71%	19%	R1, Silking
	Lewis	Dryland	209	197	239	26%	39%	35%	V18
	Nashua	Dryland	229	188	206	75%	25%	0%	V18
	Sutherland	Dryland	211	187	218	28%	62%	9%	V16
IL	Bondville	Dryland	235	225	266	17%	48%	34%	V18
	Freeport	Dryland	213	143	195	65%	35%	0%	V16
	Olney	Dryland	189	192	233	6%	35%	58%	R1, Silking
	Peoria	Dryland	210	212	240	4%	61%	36%	V18
	Springfield	Dryland	178	210	237	0%	14%	86%	R1, Silking
IN	Butlerville	Dryland	225	198	238	33%	61%	6%	V16
	Columbia City	Dryland	224	212	241	17%	67%	17%	V16
	Davis	Dryland	231	222	242	0%	100%	0%	V14
	West Lafayette	Dryland	238	228	261	0%	72%	28%	V18
KS	Garden City	Irrigated	219	200	228	14%	80%	6%	V18
	Hutchinson	Dryland	100	68	113	45%	29%	26%	R2, Blister
	Manhattan	Dryland	135	104	165	47%	17%	36%	R1, Silking
	Scandia	Dryland	132	19	81	91%	6%	3%	V16
		Irrigated	225	209	248	11%	63%	26%	V18
	Silverlake	Dryland	140	138	174	3%	40%	57%	R1, Silking
		Irrigated	210	186	224	29%	54%	17%	R1, Silking
MI	Ceresco	Dryland	177	168	231	10%	40%	50%	V14
MN	Eldred	Dryland	115	12	47	100%	0%	0%	V12
	Lamberton	Dryland	215	158	195	71%	29%	0%	V16
	Waseca	Dryland	219	202	234	22%	56%	22%	V16
MO	Brunswick	Dryland	181	188	218	5%	52%	43%	V18
	Monroe City	Dryland	172	192	233	0%	25%	75%	V18
	St Joseph	Dryland	165	186	220	14%	5%	81%	V18
ND	Dazey	Dryland	113	2	78	92%	4%	4%	V12
OH	Custar	Dryland	208	198	227	17%	61%	22%	V16
	South Charleston	Dryland	216	191	228	32%	48%	19%	V16
	Wooster	Dryland	210	210	239	6%	58%	36%	V14

§Long-term (last 20+ years) potential yield at each location and surrounding area.
¶ Range of forecasted 2021 potential yields based on average planting date in 2021, 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 2021 yield below (10%) than the long-term potential yield at each location.

Simulated Corn Stage Across 40 Locations

Corn has reached silking in Kansas, southeastern Nebraska, and southern Iowa and Illinois. In the rest of the region, corn is still in vegetative phases but it is expected to reach silking soon, especially in NE, IA, IL, IN and MO (Figure 2). Most locations are similar to or slightly behind last year’s corn development by July 14.

Figure 2. Simulated developmental stage for irrigated and rainfed corn at each location. Vn: vegetative stage (nth leaf); R1: silking; R2: blister. 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. Although it is still too early in the season, there is a relatively high probability of near-average yields for all sites. There is a high probability of near-average yield (>75%, that is, a chance of three out of four) at three sites in southcentral NE and one site in western KS. Weather conditions during the rest of the growing season will determine if most irrigated sites will have near-average yield potential.

Variable 2021 Forecasted Corn Yield Across Rainfed Locations

Forecasted yield potential is highly variable across rainfed sites (Figures 3 and 4). Overall, at this point of the season, probability of near-average yield is relatively high towards the eastern fringe of the Corn Belt (southeastern IA, IL, IN and OH). In contrast, below-average yields probability increases towards the western and northern fringes of the region due to a combination of low precipitation and high temperature. Along these lines, there is a high probability of below-average yield (>75%) at five sites distributed across ND, MN, IA, eastern NE, and northern KS. This projection may change depending on precipitation and temperature during the rest of July and August. Similarly, yields can be higher than predicted here in fields with water table as the latter can help buffer against rain-free periods. Finally, there are three sites in the southern fringe of the region (St. Joseph, MO, Monroe City, MO, and Springfield, IL) where there is a high probability (>75%) of above-average yield due to higher rainfall.

Figure 3. Vertical lines indicate the range of forecasted 2021 corn yield potential by July 13 based on average planting date in 2021 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 (2005-2020) average yield potential at each location. Separate charts are shown for irrigated corn (top) and rainfed corn (bottom).

Figure 4. Probability of the 2021 yield potential to be below (10%, green color) the long-term (2005-2020) 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

The probability for a “record yield year” for the whole country seems low considering that the probability for above average yield is small (

For rainfed corn, the scenario is diverse across regions, with higher probability of below-average yields in the north and western fringe of the region due to the limited rainfall over the past two months. Temperature and rainfall during the rest of July and early August will likely 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 early August.