1. Professor Emeritus, Dept. of Biosystem Engineering, Univ. of Arizona, Tucson, AZ 85710 (corresponding author).
2. Retired, 7413 Cinnabar Ter., Gaithersburg, MD 20879; formerly, US Dept. of Agriculture, National Resources Conservation Service, Gaithersburg, MD 20879.
3. Lynker, 3002 Bluff St., Suite 101, Boulder, CO 80301.