Smallholder System Innovations in Integrated Watershed Management, SSI Programme: strategies of water for food and environmental security in drought-prone tropical and subtropical agro-ecosystems, Tanzania and South Africa. Progress report No.4, 1 January - 31 December 2006 of the SSI Research Programme - UNESCO-IHE Institute for Water Education; International Water Management Institute (UNESCO-IHE Institute for Water Education, 2006)