Since 2006, the project BV-lac/AFD (watershed-Lake Alaotra) in the Lake Alaotra zone has developped a farming systems approach based on farmers' strategies and innovation processes including conservation agriculture (CA). The approach is based on a prospective analysis using information from farms surveys and project databases to feed a decision support system using a modelling approach. The objective is to help decision-makers to deliver better recommendations adapted to various types of farmers. The modelling tool is dedicated to search and adapt technical as well as organisational messages to local situations promoting the processes of innovation and adoption. These prospective tools equally provide an evaluation and monitoring of current actions and support the definition of elements of public policy for agricultural development.