1. Institute of Biological and Environmental Sciences, University of Aberdeen, Cruickshank Building, St. Machar Drive, Aberdeen AB24 3UU, U.K., Department of Soil Science, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh, Soil Science Department, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, U.K., and College of Physical Sciences, Chemistry, University of Aberdeen, Meston Walk, Aberdeen AB24 3UE, U.K.