Nitrate pollution remains a major problem in some parts of France, especially in the Brittany region, which is characterized by intensive livestock production systems. Although farmers must not exceed a regulatory limit of nitrogen contained in manure per hectare, many farmers in this region exceed this limit. Therefore, they must treat the excess of manure that they produce or export it to be spread in neighbouring farms and/or areas, inducing fierce competition in the land market. Another adaptation strategy consists of modifying production practices or the production system as a whole, i.e., changing the structure of the farm. In this paper, a spatial agent-based model (ABM) has been developed to assess policy options in the regulation of manure management practices. The objective is to highlight the potential effects of these policies on the farmland market and the structural changes that they induce. Our results show that the different policies, which result in similar environmental benefits, induce different changes in the land market and in agricultural structures.