[1
]Soil Physics and Land Management Group; University of Wageningen; P.O. Box 47 6700
AA Wageningen The Netherlands
[2
]Amhara Regional Agricultural Research Institute; P.O. Box +527 Bahir Dar Ethiopia
[3
]International Maize and Wheat Improvement Centre (CIMMYT); P. O. Box 1041, 00621-Village
Market Nairobi Kenya