1. Dep. of Soil Science Bayero Univ. Kano Kano 700241 Nigeria
2. Centre for Dryland Agriculture (CDA) Bayero Univ. Kano Kano 700241 Nigeria
3. School of Agriculture and Food Sciences The Univ. of Queensland Gatton QLD 4343 Australia
4. International Institute of Tropical Agriculture PMB 5320, Oyo Road Ibadan Oyo State 200001 Nigeria
5. International Maize and Wheat Improvement Center (CIMMYT), CIMMYT South Asia Regional Office, NARC Research Station Khumaltar Lalitpur Kathmandu Nepal
6. Dep. of Soil Science and Environment Univ. of Zimbabwe Mount Pleasant Harare PO Box MP 167 Zimbabwe
7. Dep. of Earth and Environmental Sciences Division of Soil and Water Management KU Leuven, Kasteelpark Arenberg 20 Heverlee 3001 Belgium