1995 General Information, Seed Sources, Weather Tables
Selection of entries. Each year, producers of hybrid seed corn in Illinois and surrounding states are invited to enter hybrids in the Illinois performance trials. This testing program is financed by a fee of $65 for each hybrid entered at a location. Most of these hybrids are commercially available, although a few experimental hybrids are also entered.
Number and location of tests. In 1995, 10 major tests were conducted at 9 locations in the state (see map). These sites represent major soil and climatic areas of the state.
Hybrids. There were 680 hybrids from 80 companies tested in 1995.
Field plot design. Three replications of an Alpha design were used to give each entry an equal chance to show its merits.
Planting Methods. All trials were planted by machine. Each hybrid plot was overplanted 30 percent and later thinned to desired stands. Each plot was four rows wide and either 23 or 25 feet long. The center two rows of each plot were harvested to determine yields.
Fertilization. All test fields were at a high level of fertility. Additional fertilizer was plowed down or sidedressed as needed to ensure top yields.
Method of harvest. All plots were harvested with a custom-built, self-propelled, corn plot combine. Shelled corn from each plot was collected, weighed, and tested for moisture content. No allowance was made for corn that might have been lost in harvest.
Grain Yield. Shelled-corn weight and moisture percentage were measured for each plot of a hybrid and converted to bushels per acre of No. 2 shelled corn (15.5 percent moisture). An electronic moisture monitor was used in the combine for all moisture readings.
Moisture content. Occasionally, hybrids too late in maturity for a given area are entered in these tests. These hybrids are often high in yield, but their moisture content may make them poor choices for farm use unless proper drying or storage facilities are available.
Erect plants. The number of erect plants in each plot of a hybrid was determined at harvest time. Any plant leaning at an angle of more than 45 degrees or broken below the ear was considered lodged. Plants broken above the ear were considered erect.
Population. Plots were overplanted and thinned to the desired population. Stand differences may be caused by failure to germinate or by damage from diseases, insects, cultivation, or rodents.
Head Exertion. Sorghum hybrids were measured in late August for length of seed head exsertion from the flag leaf to the base of the seed head (expressed in inches).
Plant Height. Sorghum hybrids were measured in late August from the ground to the top of the seed head (expressed in inches).
Head Compactness. Sorghum hybrids were rated in late August for seed head compactness. A rating of 1 was given for tightly compacted seed heads, 2 for moderate compactness, 3 for loose compactness.
It is impossible to measure performance exactly in any test of plant material. Harvesting efficiency may vary, soils may not be uniform, and many other conditions may produce variability. Results of repeated tests, like those reported here, are more reliable than those of a single-year or a single-strip test. When one hybrid consistently outyields another at several test locations and over several years of testing, the chances are good that this difference is real and should be a consideration in choosing a hybrid. When comparing yields, however, grain moisture content, percentage of erect plants, and plant population must also be considered.
A number of statistical tests are available for comparing hybrids within a single trial. One of these tests, the least significant difference (L.S.D.), when used in the manner suggested by Carmer and Swanson,1 is quite simple to apply and is more appropriate than most other tests. When two hybrids are compared and the difference between them is greater than the tabulated L.S.D. value, the hybrids are judged "significantly different."
The L.S.D. is a number expressed in bushels per acre and presented following the average yield for each location. L.S.D.'s of 10% and 30% are shown, if the 10% L.S.D. is used, decisions made are true 9 out of 10 years, the 30% L.S.D. will be true 7 out of 10 years. The 30% L.S.D. is a smaller number and will include fewer hybrids in the 'top group'. Decide the L.S.D. level that is best for your farm and find the highest yielding hybrid at the location, subtract the chosen L.S.D. level from the highest yielding hybrid, every hybrid with a greater yield than the resulting number is 'statistically the same' as the highest yielding hybrid. Consider the merits of the hybrids in this group when making hybrid selections.
In a study of the frequencies of occurrence of three types of statistical errors and their relative seriousness, Carmer2 found strong arguments for an optimal significance level in the range = 0.20 to 0.40, where is the Type I statistical error rate for comparisons between means that are really equal. Herein, values of = 0.10 and 0.30 are used in computing the L.S.D. 10- and 30-percent levels shown in the tables.
To make the best use of the information presented in this circular and to avoid any misunderstanding or misrepresentation of it, the reader should consider an additional caution about comparing hybrids. Readers who compare hybrids in different trials should be extremely careful, because no statistical tests are presented for that purpose. Readers should note that the difference between a single hybrid's performance at one location and its performance at another is caused primarily by environmental effects and random variability. Furthermore, the difference between the performance of hybrid A in one trial and that of hybrid B in another is the result not only of environmental effects and random variability, but of genetic effects as well.
1Carmer, S.G. and M.R. Swanson. "An Evaluation of Ten Pairwise Multiple Comparison Procedures by Monte Carlo Methods." Journal of American Statistical Association 68:66-74. 1973.
2Carmer, S.G. "Optimal Significance Levels for Application of the Least Significant Difference in Crop Performance Trials." Crop Science 16:95-99, 1976.
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