1. Dep. of Crop, Soil, and Environmental Sciences Univ. of Arkansas System Division of Agriculture 1366 West Altheimer Dr. Fayetteville AR 72704 USA
2. Dep. of Crop and Soil Sciences NC State Univ Raleigh NC 27695 USA
3. Dep. of Agronomy Purdue Univ. 915 West State St. West Lafayette IN 47907‐2054 USA
4. School of Environment and Natural Resources The OH State Univ. 1680 Madison Ave. Wooster OH 44691 USA
5. Water Resources Center East Carolina Univ. Howell Science Complex N108, Mail Stop 551 Greenville NC 27858 USA
6. USDA‐ARS Soil Management and Sugarbeet Research Unit 2150 Centre Ave., Building D, Suite 100 Fort Collins CO 80526 USA
7. Dep. of Plant and Soil Sciences Univ. of Kentucky Lexington KY 40546 USA
8. Dep. of Soil and Crop Sciences CO State Univ Fort Collins CO 80523 USA
9. Plant and Soil Sciences Univ. of Delaware Townsend Hall Newark DE 19716 USA
10. Agricultural Analytical Services Lab. PA State Univ. University Park PA 16802 USA