1. Conservation and Survey Div., Institute of Agric. and Nat. Res., Univ. of NebraskaLincolnNE68583‐0844
2. Water Center, Institute of Agric. and Nat. Res., Univ. of NebraskaLincolnNE68583‐0844
3. Biological Systems Eng. Dep.Institute of Agric. and Nat. Res., Univ. of NebraskaLincolnNE68583‐0844
4. Agronomy Dep.Institute of Agric. and Nat. Res., Univ. of NebraskaLincolnNE68583‐0844
5. Agronomy Dep. and Water CenterInstitute of Agric. and Nat. Res., Univ. of NebraskaLincolnNE68583‐0844