1. School of Biological Sciences, University of Aberdeen, Cruickshank Building, St Machar Drive, Aberdeen, AB24 3UU, United Kingdom, Scottish Crop Research Institute, Invergowrie, Dundee, DD2 5DA, United Kingdom, Department of Soil Science, Dhaka University, Dhaka-1000, Bangladesh, and British Geological Survey, Wallingford, Oxon OX10 8BB, United Kingdom