Projected Corn Yields Drop Below Average in Aug. 1 Model

Projected Corn Yields Drop Below Average in Aug. 1 Model

Corn ears showing pollination problems
Corn ears showing pollination problems
Figure 1. Corn ears from two corn fields in eastern Nebraska. Estimates are that 10-15% of the fields in this area are expressing tipping back and pollination problems.  Keith Glewen, extension educator in Saunders County, noted that typically, where the problems exist, 100% of the field is affected with tipping back of the ear, the most common expression.  The ears showing severe pollination problems (left) usually only account for 3-5% of the field.  (Photos by Keith Glewen)

Aug. 4, 2011

Drops at Clay Center and Mead Likely due to Continued Nighttime Highs

Projections of yield potential for irrigated corn at two sites in central and eastern Nebraska dropped below long-term averages this week, according to a model developed by UNL researchers.

Growers may want to be checking their corn fields more closely, assessing ears and, if necessary, re-estimating potential yields and market options, suggest two UNL extension educators, based on output from the model.

The trend toward average or below average yields in irrigated corn was identified for fields being modeled in Clay and Saunders counties using UNL’s Hybrid-Maize decision-management tool.

Patricio Grassini, research assistant professor in UNL’s Department of Agronomy of Horticulture, has released yield forecasts for Holdrege, Clay Center, Mead, and Concord in Nebraska; Brookings, South Dakota; and Sutherland, Gilbert, and Nashua in Iowa, based on outputs from the Hybrid-Maize model. The model used actual weather data up to Monday, August 1, and then finished the season using data based on long-term averages for each site.


View the projections of potential yield for irrigated corn in eight  locations in Nebraska, South Dakota, and Iowa, as developed with UNL's Hybrid-Maize decision management tool.  (Presentation by Patricio Grassini and Kenneth Cassman)

Forecast yields at Holdrege for irrigated corn were near or slightly above average for all planting dates. Forecast yields at Concord for rainfed corn were generally above average.

In general, forecast simulations performed for irrigated corn dropped below the long-term average for most planting dates for Clay and Saunders counties. Forecast water-limited yield potential for rainfed corn changed little from the previous week’s projections and is still above the long-term average, except at Clay Center (Table 1). In fact, at Mead rainfed yields are projected to exceed the 30-year average by 20 bu/ac. (View Grassini and Cassman's data for these sites to see how projections changed from the July 17 to the July 24 and August 1 reports.)

“I believe the reason for the sharp drop-off is due to high night temperatures, which have been well above normal,” said Ken Cassmann, UNL Heuermann professor of agronomy and horticulture, who helped develop Hybrid-Maize.  “These shorten the growing season due to accelerated development rate and result in greater losses due to respiration.”

The Hybrid-Maize tool simulates the growth of field corn under irrigated or rainfed conditions based on daily weather data, planting date, hybrid, maturity, soil type, and other factors.

The model does not simulate the specific effects of high temperatures on pollination and seed abortion, Cassman said. If these kinds of problems are occurring, the Hybrid-Maize projection will overestimate yield.

Field Observations Support Projections

The crop may look good from the road, but if growers want to verify their yield projections, they should be checking plants throughout the field to look for signs of pollination or other problems that could impact yield, advises Jenny Rees, extension educator in Clay County.

In a number of fields that Rees surveyed Monday, she found ears with blank kernels or with yellow silks intermingled with brown ones that never pollinated. Some ears had large gaps. (Rees writes about predicted corn yields in her August 1 blog post at

Tom Dorn, extension educator in Lancaster County, and Keith Glewen, extension educator in Saunders County, report similar problems in their counties in east central Nebraska. (See corn photos from Dorn in Field Updates.)

Consultants and growers have reported a lot of ears with 14 rows rather than the typical 16 or 18 rows, Glewen said. The pollination problems aren’t specific to hybrid or planting date and seem to be more common in southern Saunders County, Glewen said.

Rees and Glewen both point out that some of the ear and yield problems becoming evident now likely date back to earlier in the season.

Many corn growing areas saw harsh conditions that were not very favorable for corn early on in the growing season, when ear size is determined, Glewen said. Some areas had excessive rains and roots had ample water at the surface, but with reduced rains later in the season, plants were stressed as roots were forced to seek water deeper.

“I’ve seen some areas, particularly in northeast Nebraska, that look like they’ll be producing tremendous yields. Yields in other areas are suspect and may be at or below the long-term average this year,” Glewen said.

Lisa Jasa
CropWatch Editor


Table 1. Hybrid-Maize yield projections for corn yields in three Nebraska counties and three planting dates.  (Source:  Grassini and Cassman presentation)

Sites and Planting Dates Long-term Average
Yield Potential
(Planting Date)
2011 Forecasted Yield Potential (Median)
Clay Center, Irrigated 250 (April 27) July 17 July 24 Aug. 1
April 23   250 242 239
April 30   250 246 241
May 7   252 249 244
Clay Center, Rainfed 145 (April 23)      
April 23   134 142 132
April 30   139 145 136
May 7   139 148 145
Mead, Irrigated 241 (April 30)      
April 30   236 228 223
May 7   238 230 223
May 14   241 234 230
Mead, Rainfed 153 (April 30)      
April 30   175 171 174
May 7   179 171 174
May 14   185 182 196
Holdrege, Irrigated 247 (April 27)      
April 27   246 250 246
May 4   246 250 249
May 11   255 257 255

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