1. USDA‐ARS Agroecosystem Management Research Unit251 Filley Hall/FIC, East Campus, Univ. of NebraskaLincolnNE68583‐0937
2. USDA‐ERS Resource and Rural Economics Division355 E St., SWWashingtonDC20024
3. USDA‐ARS Wheat, Sorghum and Forage Research Unit251 Filley Hall/FIC, East Campus, Univ. of NebraskaLincolnNE68583‐0937
4. Dep. of Agronomy and Horticulture136 Keim Hall, East Campus, Univ. of NebraskaLincolnNE68583‐0915