1. Dep. of Plants, Soils and Climate; Utah State Univ.; Logan UT 84322-4820
2. Universities Space Research Assoc.; Mail Code EC3, NASA/JSC Houston TX 77058
3. Dep. of Soil, Water & Environmental Science; The Univ. of Arizona; Tucson AZ 85721
4. Lab. of Soil and Environmental Physics; Ecole Polytechnique Fédérale de Lausanne; Switzerland