The need to take into account sustainability in agricultural resource management is now universally admitted. While the term “sustainability” can mean different things to different people, it always involves a consideration of the future. From an economic point of view, sustainability can be defined as an improvement of the performance of a system so as not to exhaust the basic natural resources on which its future performance depends (Pearce et al. 1990). This definition emphasizes the importance of preserving the natural resource base.