1. Department of Soil and Geological Sciences, Sokoine University of Agriculture, Morogoro, Tanzania, P.O. Box 3008
2. Tanzania Agricultural Research Institute (TARI), Mlingano Centre, Tanga, Tanzania, P. O. Box 5088
3. Department of Agricultural Engineering, School of Engineering and Technology, Sokoine University of Agriculture, Morogoro, Tanzania, P. O. Box 3008
4. Department of Research and Development, Tanzania Agricultural Research Institute (TARI), Dodoma, Tanzania
5. Department of Biology, University of Copenhagen 2100, Copenhagen, Denmark