During the P-Imbalance project I will improve the soil scheme of the land surface model ORCHIDEE to better represent the P cycle in the soil. First, I 'll be in charge of the merge between the different versions which need to be associated for the project. Then I will co supervise the post doc and the Ph. D student who will devellop the weathering and the explicit representation of soil microorganisms. Finally, I will participate to the evaluation of the new version of ORCHIDEE including nitrogen and phosphorous cycle.