November 4, 2011

In early August, we shared in-season yield predictions from UNL's Hybrid-Maize model. The Hybrid-Maize model simulates corn yield potential under irrigated and rainfed conditions, assuming optimal crop establishment and uniformity and optimal management of nutrients, weeds, diseases, and insect pests. We showed how 2011 predicted, irrigated corn yields at two locations in Nebraska (Clay Center and Mead) had been tracking with the 30-year, long-term average yields at that point in the season.

The model showed 2011 predicted yields taking a steep drop due to high nighttime temperatures. Consistently high nighttime temperatures (minimum temperatures greater than 70°F) during late July increased nighttime crop respiration which reduced the overall net daily CO₂ uptake. This hastened crop development, which shortened the predicted duration of the crop-growing season (Table 1). By early August rainfed potential corn yields predicted for 2011 varied greatly across simulated locations due to the high spatial variability in rainfall. Depending on location, predicted rainfed yield potential was above (Mead, Nebr., Concord, Nebr., Brookings, S.D., Sutherland, Iowa) or below the 30-year predicted average (Clay Center, Nebr., and Gilbert, Iowa) (Table 1).

We continued to run in-season predictions throughout the remainder of the growing season. However, some interesting things happened with the weather this year to make irrigated yields more favorable than was predicted in early August, especially at Clay Center (Table 1). Also, simulated rainfed yields by the end of the season deviated from late July predicted yields due to changes in the amount of rainfall received during the grain filling stage compared with the period before and around silking (Table 1).

While the period from silking to beginning dent occurred in 20 days or less in several areas of Nebraska this year, the weather cooled off during the grain-filling phase (minimum temperatures around 60°F at Clay Center, Nebr. and Mead, Nebr.; Figure 1, Figure 3). Some fields stayed at ¼ starch for nearly three weeks. Looking at fields, kernels continued to get deeper, heavier, and expand to help cover some of the pollination problems observed earlier in the year.

During this time, yield predictions from the Hybrid-Maize model showed that irrigated yields had the potential of returning close to, but not at the same level, of long-term median yields (Figure 2, Figure 4). Rainfall received during the grain-filling phase was adequate to support above-average rainfed yields in the simulated locations in eastern Nebraska (Clay Center, Mead, and Concord) and central-west Iowa (Gilbert, Iowa and Nashua, Iowa). However, insufficient rainfall reduced predicted yields at two locations (Brookings S.D. and Sutherland, Iowa) compared with the yields predicted in early August (Table 1).

So what happened in your fields? Hybrid Maize predicts yields based on perfect conditions — nothing limiting and no pest/disease issues. If you aren't seeing the highest potential yields in your fields, consider the following yield limiting factors that occurred this growing season.

• In many fields, corn was planted into cool, wet soils.
• In some fields uniform stand establishment was hindered by Pythium or crop residue piles caused by floating debris after heavy rains.
• There were varying degrees of pollination problems due to high temperatures in late July (an effect not simulated by Hybrid-maize and likely to reduce actual yields). We are hearing that rainfed yields have been better than expected, but irrigated yields may be below expectations.

Regardless, yields are still very good despite another interesting growing season with many potential pitfalls due to weather events.

Jenny Rees, UNL Extension Educator
Patricio Grassini, Research Professor, UNL Agronomy and Horticulture
Ken Cassman, Professor, UNL Agronomy and Horticulture