1. Department of Sustainable Soils and Grassland Systems; Rothamsted Research; Harpenden Hertfordshire AL5 2JQ UK
2. National Soil Resources Institute; Cranfield University; Cranfield Bedfordshire MK43 0AL UK
3. British Geological Survey; Keyworth Nottingham NG12 5GG UK
4. Phil Wallace Ltd; Westland, Martlesham Heath, Ipswich Suffolk IP5 3SU, UK