1. Graduate Student, Soil and Irrigation Dept. (Associated with EEAD-CSIC), Agrifood Research and Technology Centre of Aragon (CITA), Aragon Government. Avenida de Montañana 930, 50059 Zaragoza, Spain.
2. Research Scientist, Dept. of Civil and Environmental Engineering (1372), Colorado State Univ., Fort Collins, CO 80523.
3. Dean, College of Engineering and Mathematical Sciences, Univ. of Vermont, Burlington, VT 05405.
4. Researcher, Soil and Irrigation Dept. (Associated with EEAD-CSIC), Agrifood Research and Technology Centre of Aragon (CITA), Aragon Government, Avenida de Montañana 930, 50059 Zaragoza, Spain (corresponding author).