The project Observatory for World Agricultures wants to elaborate a worldwide observatory collecting information on agriculture in different countries and its evolution. At the moment five countries have been chosen as countries of reference, Madagascar is one of them. The geographical area of the study which has been chosen is the lake Alaotra. The study of the notions of vulnerability, resilience, durability and viability has been the main point concerning the choice, the calculation and the analysis of the necessary indicators leading to the elaboration of the observatory. Three different data lines have been chosen : i) The database from the ROR, ii) The database from RFR and iii) The database from the agricultural diagnosis Bv-Lac (Durand, Nave & Penot). This paper presents some results with farming systems modeling using the two databases from the BVlac development project showing the indicators used through the example of a technical change with adoption of conservation agriculture.