In the United States, the farm bill is the primary agricultural and food policy instrument of the federal government. Every five years, Congress deals with the renewal and revision of the comprehensive omnibus bill. Congress makes amendments to provisions of permanent law, reauthorizes, amends, or repeals provisions of preceding temporary agricultural acts, and puts forth new policy provisions for a limited time into the future. Beginning in 1933, farm bills have included sections ("titles") on commodity programs, trade, rural development, farm credit, conservation, agricultural research, food and nutrition programs, marketing, etc. Some provisions are highly controversial. Provisions can impact international trade, the environment, the food supply, food safety, and the economies of rural America. Powerful interest groups are poised to intervene, including organizations of farmers (such as the American Farm Bureau Federation), as well as big agribusiness corporations (such as John Deere, Cargill, Pioneer Hi Bred International, and Monsanto). Congress is polarized along lines of ideology and interest groups. Republicans are more conservative, represent rural areas, and are tied to agricultural and businesses groups while Democrats are more liberal and tied to environmentalists, cities, and labor unions. Critics sometimes warn against putting together the agricultural and nutrition parts. However, doing so helps to bridge some of the politically relevant cultural differences that exist between legislators of urban and rural, coastal and heartland areas of the country. Traditionally, the agriculture programs have been more important for rural areas of the heartland, while urban and coastal regions have been more concerned with the nutrition assistance programs. There are stakeholders outside of the government that are also interested in food and agriculture issues. These include national farm groups, commodity associations, state organizations, nutrition and public health officials, advocacy groups representing conservation, recreation, rural development, faith-based interests, local food systems, and organic production. Putting nutrition and agriculture topics together allows for stakeholders and advocacy coalitions with different interests to find common ground on topics that are potentially contentious between them. Some of the programs that are authorized in a farm bill fall into the spending category of mandatory, while others are discretionary. Programs with mandatory funding have their funds authorized directly within the farm bill. On the other hand, programs with discretionary funding require for congressional appropriators to designate funding to them because they are not funded directly in the farm bill. Cost projections for funding estimates are calculated by the Congressional Budget Office