1. Hawkesbury Institute for the Environment; University of Western Sydney; Penrith New South Wales 2751 Australia
2. Department of Environmental Studies; University of California - Santa Cruz; Santa Cruz CA 95064 USA
3. Department of Crop and Forest Sciences - AGROTECNIO Center; Universitat de Lleida; Lleida E25198 Spain
4. USDA-ARS Cropping Systems Research Laboratory; Lubbock TX 74915 USA