1. 373 Agricultural Hall, Dep. of Plant and Soil Sciences Oklahoma State Univ. Stillwater OK 74078
2. Dep. of Agronomy Iowa State Univ. Ames IA 50011
3. Dep. of Soil Science Univ. of Wisconsin Madison WI 53706
4. Dep. of Agronomy and Horticulture Univ. of Nebraska Lincoln NE 68583
5. Dep. of Biosystems and Agricultural Engineering Oklahoma State Univ. Stillwater OK 74078
6. 369 Agricultural Hall, Dep. of Plant and Soil Sciences Oklahoma State Univ. Stillwater OK 74078
7. 044 N. Agricultural Hall, Dep. of Plant and Soil Sciences Oklahoma State Univ. Stillwater OK 74078