Analysis of Seed Protein and Oil from Soybean Northern and Southern Region Uniform Tests

Protein and oil concentration are seed constituents that make soybean [Glycine max (L.) Merr.] an important crop. Reports have been published that the oil concentration and recently the protein concentration of U.S. soybean has been decreasing with respect to other exporting countries. The objective of this study was to utilize 51 yr of two data sets, The Uniform Soybean Tests, Northern Region and Southern Region to determine long-term trends in these constituents. Oil and protein composition data of lines from Regional Summaries of Maturity Groups OO through VIII were used for the analysis. Mean oil concentration was higher in the Southern Region compared with the Northern Region (209 and 206 g kg -1 , respectively), as was protein concentration (411 and 407 g kg -1 , respectively). Maturity group means for oil and protein concentration ranged from 198 to 212 g kg -1 and 404 to 414 g kg -1 , respectively. Oil concentration increased in both data sets to 1973 and abruptly decreased in 1974 (21 g kg -1 ) to a low in 1982 (184 g kg -1 ) to higher than average values in 1983 (217 g kg -1 ) and by linear regression analysis, decreasing in the Northern Region since then. Analysis of lines evaluated from 1973 to 1974 and from 1982 to 1983 indicated that genetics was not the cause of the change in oil concentrations. Temporal protein concentrations were not as distinct as those of oil but indicated groups of years when protein concentration was above or below the mean. The data indicate that oil concentrations of soybean has been erratic and decreasing since 1974 because of unknown factors.