Conservation Reserve Enhancement Program Improvement Act of 2018 This bill modifies and provides statutory authority for the Department of Agriculture (USDA) Conservation Reserve Enhancement Program (CREP). CREP is a subprogram of the Conservation Reserve Program (CRP), under which USDA partners with states to target high-priority conservation concerns, and the states contribute funding to allow for higher CRP payments and continuous sign-ups to address the concerns. The bill directs USDA, to the maximum extent practicable, to enroll at least 3 million acres of land in CREP by September 30, 2023.