The results of the Iowa Agriculture Experiment Station Corn Yield Trials are presented annually as a service to Iowa agriculture. The single-cross data presented herein are intended to provide preliminary information on the performance of open-pedigreed hybrids produced from released and unreleased inbred lines developed at ISU as well as foundation inbred lines. We also include lines released from other public breeding programs when they become available. The information should be of value to breeders, seed producers, and others who use experiment-station-developed lines as additional sources of germplasm in breeding programs. Further information on the performance of specific hybrids remains the responsibility of the producers of these hybrids. We do not use the information in this report to recommend or endorse any particular hybrid.

In 2004, we grew two different trials—Experiment 1, an early trial representing the maturity zone north of Highway 30, and Experiment 2, which was a late trial representing the maturity zone south of Highway 30. Experiment 1 was planted at 6 Iowa locations and Experiment 3 was planted at 13 Iowa locations (Tables 1a, 1b, and 1c). Planting dates ranged from late April to early May. Most locations were harvested in October, which is normal for Iowa. The dates of planting and harvesting for each trial are shown in Table 1b and 1c. Conditions for planting, emergence, growth, and development in 2004 were excellent across the entire state resulting in record yields. Compared with 1994 (154 bushels per acre), 1995 (121 bushels per acre), 1996 (140 bushels per acre), 1997 (142 bushels per acre), 1998 (145 bushels per acre), 1999 (152 bushels per acre), 2000 (145 bushels per acre), 2001 (141 bushels per acre), 2002 (163 bushels per acre), 2003 (157 bushels per acre), the estimated average yield for 2004 for Iowa is 181 bushels per acre, which eclipses the previous record yields of 2002. We have experienced good to excellent corn yields during the past 10 years within the state. The record yields of 2004 can be attributed to excellent maize‑producing conditions with few biotic and abiotic stresses that were yield limiting.

Plots generally were 18 feet long (button to button) and included two rows spaced 30 inches (90 sq. ft. per plot) at most locations. There were minor variations in plot length among locations and cooperators, and the differences in plot size were considered in yield conversions. All yield conversions used button‑to‑button plot lengths, and actual plant stands for each hybrid yield calculation. Seedbed preparation, fertilizer application, and cultivation practices were those normally recommended for optimum corn production at the locations where the trials were grown.

All trials were planted and harvested with equipment adapted for planting and harvesting small experimental corn plots. There was no gleaning of either dropped ears or ears on broken stalks at harvest, but stand data and root and stalk lodging were recorded before harvest. Harvest losses due to root and stalk lodging and dropped ears are reflected for hybrids at the sites where lodging and dropped ears occurred.

The single-cross hybrids tested were produced between lines released by ISU and other states. Because fewer lines are being released by other public breeding programs, fewer hybrids that included lines released from other states were available for testing. Data are presented for the lines that have experiment station designations and for several experimental lines from the ISU breeding program that have survived testcross and initial single-cross evaluations.

Beginning with this 2004 report we have changed the presentation of the data on the single crosses. Data at each location were analyzed with a mixed model where reps were included as a fixed effect and entries were included as a random effect (all locations were a RCB design). Best Linear Unbiased Predictors (BLUPs) are presented for each of the traits and are listed as deviations (+ or –) from the experiment mean, which is given at the bottom of each table. Presenting the traits as BLUPs that are + or – the experiment mean allows one to immediately see if a hybrid was above or below the test mean. The disadvantage of using BLUPs is that it is harder to make statistical comparisons among hybrids. The rough equivalent of an LSD_(0.05) would be to multiply the BLUP standard error (BLUP SE, given at the end of each table) by a factor of 2. We have also presented the minimum and maximum BLUPs, genetic variance component, error variance component, and repeatability of the trial for each trait to further aid you in determining the quality of data at each location.

Data combined over environments were similarly analyzed with a mixed model with all factors being fixed except for entries and the entry x location interaction. Otherwise, the data presentations for the combined analyses are similar to those for the individual location analyses. In addition to the information presented at the end of the individual location tables, for the combined location tables we have provided the G x E variance component, the number of replications per environment, and the total number of environments of data available for each trait.

All data are now presented in English units. Units for each trait are given in the column headers, and the units apply to both the experimental means as well as the BLUPs. For example, the numbers in the Plants Per Acre column need to be multiplied by 1000 to get actual plants per acre. The Adjusted Value column was calculated assuming $2.20 per bushel for corn, 1.35% shrinkage, and $0.035 per bushel per point drying cost.

This is the first year that we have not provided data combined over years for each individual location and combined over all locations. The reason for this is that there were few hybrids grown in 2004 that were also grown in 2003 or 2002. The 2005 report will see a return to multi-year data, as we think this is important in determining hybrid performance.

In addition to evaluating single crosses, we also evaluate inbred line performance and report data on several inbred characteristics. These data are only collected on coded experiment station inbreds and on experimental inbreds from the ISU corn breeding program. Inbred data can be found in Table 23 of the report. These data are not reported as BLUPs. They are the actual values of the mean of 2 replications at a single location.

Table 24 of the report contains the publicly available pedigrees or derivations of the inbreds evaluated in single cross combinations.

Of the 19 locations grown in 2004, 9 were grown by the ISU corn breeding program and 10 were grown by commercial plant breeders. We appreciate and value the industry support we receive for this trial, and would like to acknowledge the corn breeders and their companies for growing this test for us. The industry cooperators are listed in Table 1b and 1c of the report.

An electronic version (PDF format) of this document is available at http://www.agron.iastate.edu/corn/data/