During the last decades there were huge changes in the Argentinean farming sector, among which stands out the fact that the new business model (known as sowing pools) do not rely on buying the land, but on leasing it. As a consequence farmland leases spread all over the country while environmental conflicts related to unsustainable farming practices escalates. In this context we review the lessor environmental duties under the National Constitution, the Environment General Act, the new Civil and Commercial Code and the Farm Lease Act. We conclude that the lessor is obliged to supervise that the lessee won’t undertake unsustainable activities, and therefore can be held responsible if he fails to perform his duties and third parties are damaged.