At first, I was going to say, "developed nations, not developing nations, are our major agricultural export partners," but the USDA's website provides pretty strong data showing how much many developing countries receive from us.
Warning: The following link is an Excel file: USDA's year-by-year US agricultural exports. Well, there's little doubt that market forces contributed as much to the Late Victorian famines in China, India, and South America as much as climatic factors, so obviously market decisions can cause famine. The group of 33, mostly developing countries within the WTO, make a strong case for agricultural tariffs to protect their markets.
Ok, let's assume that we don't export any food at all, and we respect the group of 33's demands regarding agricultural protectionism. Would it be better for the U.S. to import foreign, lower cost, foods, reducing the supply of American crops? Is being dependent on foreign food good for our economy?