Amendment 1, known as the "right to farm" amendment, gives residents of the state the right to "engage in farming and ranching practices." It passed by only 2,528 votes out of about 995,000.
Kevin Flannery, a spokesman for the Missouri secretary of state, said anyone who voted against the amendment can request a recount because it passed by less than .5 percent of the total vote Tuesday.
If the amendment stands, Missouri will be the second state to provide similar protection for farmers. North Dakota already has a right to farm clause in its constitution.
Opponents argued the amendment will do little to help family farmers while protecting large corporations involved in agriculture from scrutiny.
Blake Hurst of the Missouri Farm Bureau said that the amendment would allow farmers to continue doing what they are already doing. It would protect "practices that are proven, that are safe, that are good for consumers, good for farmers and good for the environment," he told National Public Radio.
But not all farmers supported the amendment. Jeff Jones, who farms in Callaway County in central Missouri, told NPR he is worried about an industrial hog operation that plans to locate a half-mile uphill from the land his family has farmed for four generations. He said that in a heavy rain fertilizer would be washed onto his farm, and the amendment could bar him from legal action.