Vegetable and Corn Yields in the United States, 1900-Present

Abstract

-1 . The average yield for the 1990s was 7839 kg·ha -1 , 5 times the yield of the 1930s. A number of researchers have studied the basis for this increase by partitioning the contributions of improved genetics from those of improved management. Systematic studies performed by Duvick (1992) on corn hybrids grown from 1930 to 1989 in cen- tral Iowa demonstrated a linear increase in yield for the duration of this time period. An equivalent of 56% of the annual average gain in Iowa corn yields for this period was determined to be attributable to the ge net ic improvements of these hybrids (Duvick, 1984, 1992). It is clear from Duvick∑ s studies that much of the genetic change is represented by increased inputs and stress associated with high input intensive man age ment systems. Modern corn is much more resistant to drought stress associated with high population densities (30,000 plants/ha, 1930s; 80,000 plants/ha, 1980s) (Duvick, 1999). High levels of nitrogen fertilizer in creas es stalk lodging in grain crops. Modern corn is more resistant to stalk lodging than corn from the 1930s. High population den si ties also increase stalk lodging. Thus, in corn genetic changes were required for optimum use of increased inputs and higher population densities. In order to carry out comparative studies, seed of cultivars repre- senting different eras must be obtained, planted, and evaluated un der controlled conditions at a number of lo ca tion × year combinations. The experiment should include multiple production practices, re flect ing current management practices as well as older practices. Such studies have been con duct ed in a number of agronomic crops (soy bean (Glycine max L. Merrill), Specht and Williams, 1984; barley (Hordeum vulgare L.), Wycham and Rasmusson, 1983; sorghum (Sorghum bicolor L. Moench), Miller and Kebede, 1984), and in most cases large portions of the overall yield gain have been attributed to progress from plant breeding. However, Douches et al. (1996) found little influence of genetic improvement in the large increases in potato (Solanum tu- berosum L.) yields in the United States since the 1920s. Those workers found most of the gains from breeding programs during this period were associated with early maturity and improved tuber appearance. Thus, the primary reason yields increased was likely improvements in production practices.