[1] Univ Illinois, Urbana, IL 61801 USA
[2] Iowa State Univ, Ames, IA USA
[3] USDA ARS, Jackson, TN USA
[4] So Illinois Univ, Carbondale, IL 62901 USA
[5] Purdue Univ, W Lafayette, IN 47907 USA
[6] Univ Missouri, Columbia, MO USA
[7] Agr Consulting & Testing Serv Inc, Carroll, IA USA