Traditional ex post impact assessment methods such as benefit cost analysis or productions functions use cannot take into account the complexity of change in natural resource management processes that are dynamic and interactive. This paper proposes to use a bio-economic model based on linear programming to valuate the ex post impacts of NRM researches. This model is used to valuate the impacts of spine less cactus -alley cropping system in the arid and semi arid area of Maghreb. The case study is the Zoghmar community in the Central Tunisia, the area covered by the Mashreq/maghreb Project, the Femise project and the SPIA Project (ICARDA projects). This community is located in dry lands characterized with less than 350 mm rainfall and periodic droughts. Agro-pastoral systems are dominant production systems, and people derive their incomes from both livestock and crop production. The main results imply that the implemented technology has basically benefited to small farmers with a ewe capital inferior to 30 heads.