1. UMR G-eau, SupAgro, 2, place Pierre Viala, 34060 Montpellier Cedex 5, France (corresponding author).
2. LyRE, Research and Development Center, Lyonnaise des Eaux, Bordeaux, France.
3. West Consultants, 8950 South 52nd St., Suite 210, Tempe, AZ 85284-1043.