The project aims at characterizing phosphorus availability in arable soils of the central highlands and eastern region of South Vietnam. The effectiveness of different sources of P and their combinations for different crops will be determined and economi- cally sound methodologies for the replenishment of P-capital will be developed. A particular emphasis goes to the unraveling of processes underlying the observed increase in P-availability fol- lowing the application of rock phosphates and green manure. The project finally addresses the relation between soil parameters and practical measures to improve and/or maintain P-availability, so opening the possibilities for extrapolation to similar situ- ations. Apart from basic research a process level, due attention is goven to (i) training Vietnamese staff and (ii) disseminate findings to farmers, extension officers and scientists.