Corn and Dry Soils at Planting, Looking Ahead to 2013 - Part II

February 11, 2013

Part II: Hybrid Reltive Maturity Changes

By Roger Elmore, Department of Agronomy

In Part I of this article, I addressed the current situation and Iowa corn performance in 2012. In that article, I discussed modeled results relating to whether or not we should alter seeding rates if soils are dry at planting this spring. Here I intend to discuss how changing hybrid relative maturities affects yield with different starting points for soil moisture.  I addressed both of these issues in January 2012 in a series of three ICM News articles.

Some may know that in more southern parts of the Corn Belt, farmers often plant hybrids that are 5 to 10 or more days earlier than typical adapted hybrids in an effort to avoid late-summer heat and drought.  Will this approach work in Iowa if our soils remain dry at planting?
Should you consider planting earlier-season hybrids if it is dry at planting in 2013?


As in the other article of this pair, I used a corn simulation model (Hybrid-Maize) to answer this question. The model uses historic weather data from automated weather stations. I used data from seven of Iowa State University's Research and Demonstration Farms, one in each of the four corners of Iowa, one in both west central and northern Iowa, and another near Ames in central Iowa.

The model allows users to change soil moisture conditions at planting to simulate different possibilities. With this capability, we can address the question, “What if the soils are only one-quarter field capacity (FC) at planting?”

I compared two moisture levels:

  • A ‘normal:’ 75 percent field capacity (FC) in the topsoil (0-12 inches) and 100 percent FC in the subsoil (12-40 inches), and
  • B, ‘very dry:’ 25 percent FC in both topsoil and subsoil.

I realize that some Iowa soils now are perhaps wetter than 25 percent FC so the second possibility may be pessimistic for those areas. Other common inputs for each site modeled are provided in Table 1 (with the exception of hybrids). Factors that varied across locations such as soil textures are shown in Table 2.


Table 1. Hybrid-Maize model input factors that were the same across locations and years


Factor Input Value/ Date

Emergence date

1 May

Plant population

32,000 plants per acre

Soil moisture


Situation A (Normal)


Top soil

75% Field Capacity

Sub soil

100% Field Capacity

Situation B

(Very Dry)


Top soil

25% Field Capacity

Sub soil

25% Field Capacity

Rooting depth

40 inches


† Year when automated weather data collection began
‡ Si = Silt, Cl = Clay, Lo = Loam.
§ GDU = Growing Degree Units; 2300 = about 95 RM; 2400 = about 100 RM; 2500 = about 105 RM; 2600 = about 110 RM.

Given the two soil moisture situations at planting discussed above, the model allows us to simulate the effects of changing hybrid maturities. It assumes a generic hybrid and models corn growth based on temperature, solar radiation and precipitation actually recorded in the weather database for each research farm. I compared three hybrids at each location: a full-season and two earlier-season hybrids. The full-season hybrids at the northwest (NW), northern and northeast (NE) locations required 2500 GDD (about 105 days RM) while the early-season hybrids required either 2400 or 2300 GDD (about 100 and 95 days RM, respectively). At the west central, central, southwest (SW), and southeast (SE) locations, the full-season hybrids required 2600 GDD (110 days) and the early-season hybrids required either 2500 or 2400 GDD (about 105 and 100 days RM, respectively).

Simulation Results

At all locations, the longest-season hybrids out-yielded shorter-season hybrids in at least three-quarters of the modeled years in each of the respective databases. That was true whether soil profiles were wet at planting or very dry (Table 3).  There were both high-yielding years and low-yielding years in which the short-season hybrids yielded more than the full-season hybrid (data not shown). However, at all locations, there was a tendency at higher yield levels for the differential to widen between the full-season hybrid and the very-early hybrid with the full-season hybrid yielding more.  At low yield levels, as in 2012, there was little yield difference among hybrids.

† The full-season hybrid outperformed both earlier-season hybrids at all locations and with both soil conditions at planting in 2012.

The analysis shows that hybrids of both maturities should be grown, similar to last year’s conclusion. This will spread risk and maximize yields over years.  Nevertheless, the data suggest planting most of your acres in what could be considered full-season hybrids for your area.

These simulated data results mirror actual yields obtained from the ISU/Iowa Crop Improvement Association’s Crop Performance Test – Corn. These tests are conducted annually at 20 or more locations with a full-season and an early-season hybrid trial at each site. Means of the two trials in any specific region are usually similar. Again, this suggests planting both early- and full-season hybrids are important to maximize yields while spreading risk.


Many things can happen between now and planting in 2013. If soil moisture conditions do not improve, planting diverse hybrids with a range of maturities is a good approach…as it is every year. Meanwhile, as before, let’s hope for complete recharge of our soil before planting.


The two articles in this series summarize portions of the 2013 Crop Advantage Series (CAS) talks presented in January 2013.

Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by email at or 515-294-6655.

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on February 11, 2013. The information contained within may not be the most current and accurate depending on when it is accessed.

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