The relationship of corn and soybean yields in 2003 is an unusual event and unlikely to recur with frequency in the future, according to a University of Illinois Extension report.

"After comparing 2003 corn and soybean yields to historic yields for those crops, it is clear that the 2003 corn yield was considerably above average and the 2003 soybean yield significantly below average," said Gary Schnitkey, U of I Extension farm management specialist. "Having an above-average yield in one crop and a below-average yield in the other crop is highly unusual."

Schnitkey's report, "What Do 2003 Corn and Soybean Yields Indicate about Future Yields?" can be accessed on farmdoc at: http://www.farmdoc.uiuc.edu/manage/newsletters/fefo03_22/fefo03_22.html .

He noted that the 2003 yields do not suggest that the long-term relationship between corn and soybean yields has changed.

Since 1972, the Illinois trend-line corn yield has increased each year by about 1.45 bushels per year.

"The 2003 projected yield of 169 bushels per acre represents the highest corn yield that has ever occurred in Illinois," Schnitkey said. "That yield is 21 bushels above the trend-line yield of 148 bushels per acre. The last time the actual yield was above the trend-line yield by more than 20 bushels was in 1994. In that year, the actual yield of 156 bushels was 23 bushels above the trend-line yield of 133 bushels."

Looking at state average soybean yields during the same period shows the trend-line yield increasing an average of 0.42 bushels per year. The 2003 projected soybean yield is 37 bushels per acre; however, it is seven bushels below the trend-line yield of 44 bushels per acre.

"While below average, the 2003 is not the worst soybean yielding year," Schnitkey noted. "Actual soybean yields were significantly below trend-line yields in 1974 by eight bushels, in 1983 by seven bushels, and in 1988 by 11 bushels.

"Since 1988, however, soybean yields have not exhibited much variability. This long period of relative stability was finally broken in 2003. What may be more unusual than the below-average yield in 2003 is the relatively stable period from 1989 through 2002."

By comparing corn-soybean ratios from 1972 through 2003, it appears that corn yields relative to soybean yields have been stable. This suggests that the 2003 relationship of the yields is an infrequent occurrence.

"Some have suggested that 2003 indicates that corn yields continue to outpace soybean yields," he added. "An examination of historic yields questions this viewpoint. With exceptions in the southern part of the state, corn yields relative to soybean yields have been relatively stable in most areas of Illinois prior to 2003."