Preserving Marginal Lands and Protecting Farming Act of 2013

Preserving Marginal Lands and Protecting Farming Act of 2013 - Amends the Food Security Act of 1985 to set the maximum number of acres that may be enrolled at any one time in the conservation reserve program (CRP) at: (1) 29 million acres for FY2013, (2) 26 million acres for FY2014, and (3) 26 million acres for each of FY2015 through FY2018.

Prohibits the enrollment of land in the conservation reserve that is classified as class I or class II land under the National Soil Survey Handbook's land capability classification system unless such land is enrolled as a buffer, filterstrip, or strip adjacent to a riparian area.

Directs the Secretary of Agriculture (USDA), during FY2014, to permit a participant that entered into a CRP contract to terminate the contract at any time if the contract has been in effect for at least five years.

Revises the types of land that are not subject to early contract termination.