We present the impact of the farms heterogenity on the promotion of non-commodity outputs on a French case study. We show that the large heterogeneity of the ratio of the amount of non-commodity outputs supplied by the farms can be captured by a one-dimensional parameter : the type of the farm. Second, using the relationship between the amount of non-commodity and commodity outputs supplied by the farms and their types, a regulator can design an optimally differentiated policy to promote the supply of the non-commodity output without weakening too much the supply of the commodity output and the farmers' revenue.