1. Agricultural engineer, Columbia, Missouri 65211, U. S. Department of Agriculture, Agricultural Research Service.
2. Plant physiologist at Fort Collins, Colorado 80523, U. S. Department of Agriculture, Agricultural Research Service.
3. Soil scientist at St. Paul, Minnesota 55108, U. S. Department of Agriculture, Agricultural Research Service.
4. Professor in the Department of Soil Science, University of Wisconsin, Madison 53706.