1. USDA-ARS; Adaptive Cropping Systems Lab.; Beltsville MD 20705
2. Dep. of Plant Science and Landscape Architecture; Univ. of Maryland; College Park MD 20742
3. Dep. of Agronomy; Iowa State Univ.; Ames IA 50011
4. USDA-ARS; National Lab. for Agriculture and the Environment; Ames IA 50011
5. Dep. of Agricultural and Biological Engineering; Iowa State Univ.; Ames IA 50011
6. LI-COR Biosciences Inc.; Lincoln NE 68504