Corn and Soybean Yields: Historical Trends and Future Prospects.

Steadily increasing crop yields have played a major role in delaying a Malthusian crisis for the last half-century. These increases may not be enough, however, to meet future demands fueled by continued population growth, higher standards of living and the diversion of food crops to fuel production. I evaluated historical yield trends of corn (Zea mays L.) and soybean [Glycine max (L.) Merrill] to gain some insight into the potential for continued or accelerated yield increases in the future. Yield plateaus may occur first in high yield environments so I analyzed county soybean yield trends from 1972 to 2003 (215 data sets from Nebraska, Iowa, Kentucky and Arkansas), but I found significant evidence of plateaus in only 3 of the 168 counties with increasing yield. There were, however, 47 counties with no significant change in yield during the 31 year period. These counties included non-irrigated low yield counties in Arkansas (21) and Nebraska (20), and six counties in Kentucky [four of the six had more than half of their production grown as a second crop after winter wheat (Triticum aestivum L.)]. The ratio of average state corn yield to soybean yield increased steadily from 1.5 to 2.0 in 1950 to approximately 3.0 in the early 1970’s (Iowa, Illinois, Indiana) or the 1980’s (Kentucky, Missouri, Tennessee) and then there was no significant change through 2003 in all six states. I found little evidence in this analysis that either corn or soybean yields have reached a plateau in any of the six states. Future yield growth will no doubt continue to benefit from contributions from traditional plant breeding and from the application of biotechnology to plant improvement, but there may be negative affects of climate change. Considering past successes, it is easy, in my opinion, to remain optimistic about the future.