Effects of Changes in Climate and Weather Variability on the Yields of Corn and Soybeans

Abstract

A crop/weather model was used to analyze the effects of weather and technology on the yields of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] in Illinois and Iowa. These two states are in the center of the U.S. Corn Belt and produce about one-third of the nation's corn and soybean. The warming trend in July and August from 1891 to 1936 adversely affected corn and soybean yields. The cooling trend from 1936 to 1972 was accompanied by increased rainfall in July and August and decreased variability in simulated yields. The improvement in weather and climate accounted for about 20% of the increase in yield of corn and soybean from 1936 to 1972. There has been increased weather variability since 1973, with both higher and lower yields than occurred in the previous 18 yr. There has been a cyclical pattern of summer weather of about 18 to 19 yr in Illinois and Iowa. A cluster of 4 to 5 yr of unfavorable weather has been followed by a cluster of 5 to 6 yr of very favorable weather in every cycle of 18 to 19 yr. The cycle of favorable years since 1891 centered on 1905, 1923, 1942, 1960, and 1979. The weather cycle has the same length as the lunar nodal cycle. The link between the lunar cycle and crop yields may be through changes in the temperature of surface waters of the Pacific Ocean and their effects on atmospheric circulation. Of the drought years identified in the study, not one was in a year of an El Nino event from 1868 to 1982.