1. Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana IL 61801.
2. Department of Agricultural Engineering, University of Illinois, Urbana IL 61801.
3. Archer Daniels Midland Company, 1001 Brush College Road, Decatur, IL 62521.
4. Corresponding author. Phone: 217/244-1115. Fax: 217/333-9817. E-mail: dbriskin@uiuc.edu