Corn Grain Yields, 1870 to 1930
From 1870 until about 1930 there was no increase in the U.S. national average corn grain yield (Figure 7). The average yield in the decade of the 1920s was 26.4 bushels per acre (1.8 tons/hectare), which actually was a bushel per acre less than occurred 50 years earlier. What were the reasons for this lack of response?
- Grain productivity is difficult to change when selection is based on the performance of individual plants and when grain yield is judged visually from the apparent size of ears (grain and cob).
- When selected ears are open-pollinated ears (i.e. the source of the pollen is not controlled), the effectiveness of selection is reduced because pollen from less desirable (non-selected) plants has pollinated some of the kernels on those selected ears.
- Selections often were based on characteristics that had nothing to do with actual grain productivity. This apparent contradiction to good farming practices reached its peak of popularity in the corn shows.