1. Environmental Soil Chemistry Research Group, Department of Plant and Soil Sciences, 152 Townsend Hall, University of Delaware, Newark, Delaware 19717-1303, USDA-ARS, Animal Manure and Biproducts Laboratory, Beltesville, Maryland 20705, University of Chicago, Consortium of Advanced Radiation Sciences, Advanced Photon Source, GSECARS, Argonne, Illinois 60439 USA, and Department of Geophysical Sciences, University of Chicago, Chicago, Illinois 60637