1. Agricultural Research Council, Letcombe Laboratory, Wantage, Oxfordshire
2. Ministry of Agriculture, Fisheries and Food, Agricultural Development and Advisory Service, Coley Park, Reading, Berks
3. Soil Survey of England and Wales, Rothamsted Experimental Station, Harpenden, Herts
4. Scottish Institute of Agricultural Engineering, Bush Estate, Penicuik, Midlothian