Agriculture Improvement Act of 2018 This bill (commonly known as the farm bill) reauthorizes through FY2023 and modifies Department of Agriculture (USDA) programs that address: commodity support, conservation, trade and international food aid, nutrition assistance, farm credit, rural development, research and extension activities, forestry, energy, horticulture, and crop insurance. The bill modifies agriculture and nutrition policies to: require farmers to make a new one-time election to obtain either Price Loss Coverage or Agricultural Risk Coverage for the 2019-2023 crop years; replace the Dairy Margin Protection Program with Dairy Risk Coverage and modify coverage levels and premiums; make Indian tribes and tribal organizations eligible for supplemental agricultural disaster assistance programs; reduce the adjusted gross income limitation for receiving benefits under commodity and conservation programs; modify funding levels and requirements for several conservation programs, consolidate several existing trade and export promotion programs into a new Priority Trade Promotion, Development, and Assistance program; legalize industrial hemp and make hemp producers eligible for the federal crop insurance program; establish an interstate data system to prevent the simultaneous issuance of Supplemental Nutrition Assistance Program (SNAP, formerly known as the food stamp program) benefits to an individual by more than one state; increase the loan limits for farm ownership and operating loans; modify the experience requirement for farm ownership loans; authorize a categorical exclusion from requirements for environmental assessments and environmental impact statements for certain forest management projects with the primary purpose of protecting, restoring, or improving habitat for the greater sage-grouse or mule deer; and modify the organic certification requirements for imported agricultural products.