The
research for this thesis was carried out at the University of
Tropical Agriculture (UTA) in
I would like to thank the Swedish Agency for Research Cooperation with Developing Countries (SAREC) for funding this study through the regional MEKARN project, and all friends and UTA staff (Lylian Rodriguez, Pol Samkol, Hean Pheap and Srey Sam An) for their help during the experiments. I express deep gratitude to my parents and wife for their encouragement and very strong support during this study.