1USDA‐ARS National Agric. Water Quality Lab. P.O. Box 1430 Durant OK 74702‐1430
2CADSWES, Univ. of Colorado Boulder CO 80309‐0421
3Wisconsin Dep. of Nat. Resources Madison WI 53707
4Dep. of Plant Science Univ. of Delaware Newark DE 19717‐1303
5Dep. of Agronomy Univ. of Arkansas Fayetteville AR 72701
6Soil Science Dep. Univ. of Florida Gaineseville FL 32611