1. Biological Systems Engineering Dep. East Campus, Univ. of Nebraska‐Lincoln 5223 L.W. Chase Hall P.O. Box 830726 Lincoln NE 68583‐0726 USA
2. Biosystems and Agricultural Engineering Dep. Univ. of Kentucky 128 Barnhardt Lexington KY 40506 USA
3. USDA‐ARS, Agroecosystem Management Research Unit 251 Filley Hall, UNL East Campus Lincoln NE 68583 USA
4. School of Natural Resources Univ. of Nebraska‐Lincoln East Campus Lincoln NE USA
5. Water Sciences Laboratory Univ. of Nebraska‐Lincoln East Campus, 1840 N. 37th Street Lincoln NE 68583‐0844 USA