1. USDA-ARS National Laboratory for Agriculture and the Environment; USDA-ARS National Lab. for Agric. and the Environ.; 2110 University Boulevard Ames IA 50011
2. Desert Research Institute; 755 E. Flamingo Road Las Vegas NV 89119
3. University of Kiel, Kiel University, Institute of Soil Science; Plants, Nutrition, Olshausenstr; 40, Kiel, 24118 Germany