1. The purpose of the 1939 Iowa Corn Yield Test was to determine for each district and section of the state those kinds of corn which perform best.
2. The state was divided into four sections for the tests. Each section was composed of three districts in each of which was located a testing field.
3. A total of 1,214 district entries was made in the 12 fields. These entries were divided into two classes, regular and experimental, depending upon the quantity of seed indicated to have been grown by the entrant in 1938.
4. The seed for planting the entries in the regular class was obtained by the Iowa Corn and Small Grain Growers’ Association from warehouses, on the open market and from farmers who had purchased the seed to plant. The seed for planting the experimental entries was supplied by the entrant.
5. Each regular entry was planted in 10 plots and each experimental entry in five plots in each field where tested.
6. Data were obtained for each entry on percentage stand, ear height, acre yield, percentage lodging, moisture content, percentage of dropped ears and damaged kernels.
7. A performance score was computed for each entry. In computing this score the yield was weighted 50 percent, dry corn 20 percent, and lodging resistance, ears on stalks and undamaged kernels 10 percent each. The entries are arranged in tables 7 to 22, inclusive, according to their performance score.
8. The difference in yield necesary to be considered significant was calculated and is included in the performance data for each district and each section. Because of the increased number of replications in the regular classes the bushels necessary for significance are generally smaller than in the experimental classes.
9. The average yield, moisture percentage and percentage of lodged plants for those section entries which were in the 1939 test and in tests of the same previous years were calculated. These data offer a more reliable basis for predicting the future performance of these entries than the results of any one year.
10. The long ripening season of 1939 permitted late, unadapted kinds of corn to mature in the Northern Section where they normally would be too late. Many of the hybrids which performed well in the Northern and North Central sections might be wholly unsatisfactory in a season with a less favorable fall.
11. The average yield of all hybrids was greater than that of the open-pollinated varieties in each of the 12 districts. The average advantage of the hybrids for the entire state was 14.0 percent. All of the hybrids in the test, however, were not superior. In 6 of the 12 districts the lowest yield was made by an open-pollinated variety, in 2 by an experimental hybrid and in 4 by a regular hybrid.
12. Differences in yield between hybrids with identical pedigrees may be largely accounted for by differences in percentage of stand. The use of proper seed stock, proper isolation and good detasseling are very necessary, but the maximum yield from a certain combination can be obtained only when the seed is processed and planted in such a manner that a high germination results.
13. The Banner Trophy was awarded to William Dockendorff & Sons on the basis of the performance of an entry of Iowa Hybrid 939 made by them in the Northern Section. This hybrid had a performance score of 108.73. It yielded 16.9 percent more than the average of the entries in its class and exceeded the yield of the average of the open-pollinated varieties by 20.8 bushels to the acre. This entry had a higher than average percentage of dropped ears and a lower than average percentage of lodged plants.
Robinson, Joe L. and Zuber, Marcus S.
"1939 Iowa corn yield test,"
Bulletin P: Vol. 1
, Article 1.
Available at: https://lib.dr.iastate.edu/bulletinp/vol1/iss2/1