1. Dep. of Agronomy Iowa State Univ. 716 Farmhouse Ln. Ames IA 50010 USA
2. Dep. of Earth and Environmental Sciences Michigan State Univ. 288 Farm Ln. East Lansing MI 48823 USA
3. Dep. of Crop and Soil Sciences Univ. of Georgia Athens, 3111 Carlton St. Athens GA 30602 USA
4. Practical Farmers of Iowa 1615 Golden Aspen Dr. Ames IA 50010 USA
5. W.K. Kellogg Biological Station Michigan State Univ. 3700 E Gull Lake Dr., Hickory Corners East Lansing MI 49060 USA
6. Dep. of Agronomy and Horticulture Univ. of Nebraska–Lincoln 1875 N. 38th St., Plant Sciences Hall Lincoln NE 68583 USA